This PDF file contains the front matter associated with SPIE Proceedings Volume 11047, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

In oncology, cancer radiotherapy is a well-established therapeutic technique for more than 100 years and, worldwide, about two-thirds of all cancer patients will undergo conventional X-rays or gamma-rays therapy, as monotherapy or as part of their treatment, to destroy tumor cells by damaging their DNA. As the high energy electromagnetic waves based radiotherapy is not equally effective in all types and location of cancerous tumors, radiotherapy using accelerator based hadron beams is a well-established alternative, especially for deep-placed tumors, as a result of the well-known Bragg peak phenomenon. External proton beam radiation therapy is most commonly used in the treatment of pediatric, central nervous system and intraocular cancers. To overcome the major obstacle of the very expensive proton production facilities (through accelerators) in building of proton cancer treatment medical centers, the use of high-power lasers for particle radiation production was proposed. The recent development of lasers with ultrashort pulses (e.g. with pulse lengths around 30 fs) resulted in particle acceleration from the rear side of a laser-irradiated thin foil, based on their unique properties and laser-matter interaction mechanisms. In this review work, we aim to present the progress toward laser-driven radiotherapy, as well as to discuss if and how the radiobiological effectiveness of particle radiation generated by lasers differs from that provided by other conventional techniques. We will discuss the expectations and limitations in anti-cancer laser-driven proton therapy, reported in literature over the last decade. In the framework of the national project HELLAS-CH, we will present some of the preliminary efforts on the combined photodynamic and ionizing radiation action, with ultra-fast laser pulses, on tissue simulators and biological samples.

The recent advancements of three laser-based diagnostic technologies developed at the Riga group are briefly reviewed: (i) RGB imaging of cw-laser excited skin autofluorescence intensity and photobleaching rate distributions, (ii) ps-laser excited skin autofluorescence and diffuse reflectance kinetics analysis, (iii) snapshot RGB skin chromophore mapping under triple-laser illumination. These techniques have passed preliminary laboratory and clinical tests which have demonstrated a promising potential for further implementation in portable devices for routine clinical applications. Operation principles, set-up schemes and some clinical results obtained by the above-mentioned techniques are discussed in this paper.

In the current study were used excitation-emission matrices (EEMs) and synchronous fluorescence spectroscopy (SFS) steady-state techniques in a broad spectral regions (excitation at 220-500 nm and emission at 280-850 nm) to achieve the whole set of endogenous fluorophores, existed in normal and neoplastic cutaneous tissues. Several types of benign, dysplastic and malignant types of skin lesions were investigated ex vivo using both EEM and SFS modalities, namely the basal cell papilloma and carcinoma, pigmented nevi, dysplastic nevi, squamous cell carcinoma and malignant melanoma. Histological analysis was used as a “gold standard” for evaluation of clinical diagnosis of the lesions investigated. Comparison with the normal skin tissue spectral data was made, based on the signals detected from the safety margins areas of the surgically excised tumours. EEM and SFS data reveal statistically significant differences between variety of benign, dysplastic and malignant lesions, which could be used as fingerprints, applicable for differentiation algorithms. In a few of malignancies endogenous porphyrins signals were even observed, but in general the fluorescence signals were addressed to the coenzymes, such as NADH, flavins; structural proteins, such as collagen, elastin and their cross-links, as well as keratin in the case of basal cell lesions. Pigments, such as hemoglobin and melanin distorted the signal due to intrinsic fluorophores signal reabsorption, what has to be taken into account when the algorithms for discrimination of the pathology types are developed.

Apart from the huge physiological importance of hemo-, myo- globin and hemin, they play also an important role as robust and effective recognition agents in chemical and biological sensors. In this aspect the key factor in developing a reliable biosensor is the immobilization on the transducer. Usually immobilization can be produced by chemical methods, but there is frequently a need for homogeneous films of well-controlled thickness or films which can be deposited in a dry environment. The film thickness is of main importance for the optical transducer detected by Surface Plasmon Resonance (SPR) what is used in our study. Hundreds of immobilization protocols have been developed in an effort to ensure high performance sensing. All of them are focused on finding and deposition of appropriate matrices in which the recognition medium can be incorporated. However, the matrix always deteriorates the effectiveness of recognition. It seems that the best approach is to perform direct immobilization of the recognition medium. However, this is not always possible regarding the organic materials – the problem is whether the deposition retains the bioactivity of the recognition agent. On the other hand, the type of the transducer also imposes constrains. For example, the direct immobilization of the proteins is not possible for electrochemical sensors, because of the distance between the redox center and electrodes is too long. Evaluating the pros and cons of organic (protein) film deposition we have considered to study the possibility for direct immobilization of myoglobin, hemoglobin and hemin on SPR transducer. To best of our knowledge, SPR biochip with immobilized myoglobin, hemoglobin and hemin has never been constructed before. We have used spin coating, for direct immobilization and matrix-assisted pulsed-laser evaporation (MAPLE) for elaboration of the SPR biochip. The performance of both SPR chips – direct and MAPLE immobilized, was studied by SPR registration of the binding activity of myo- and hemo- globin ligands with carbon monoxide (CO), carbon dioxide (CO₂) and nitride oxide (NO).

In the present work we have investigated the in vivo effect of tissue temperature and laser parameters on the quantum efficiency of laser-induced photodissociation of oxyhemoglobin (HbO₂) in cutaneous blood vessels by measuring the change in the oxygen saturation of arterial blood. Arterial oxygen saturation (SaO₂) was measured using the method of fingertip pulse oximetry. It is shown that there is a local decrease in the local oxygen saturation upon laser irradiation by approximately 10% . Raising the local temperature of the skin tissue up to 42°C leads to an increase in the quantum efficiency of the photodissociation of HbO₂ by approximately 1,5% upon irradiation with a wavelength of 860 nm. The obtained results can be used in the clinical phototherapy practice.

The implementation of tissue polarimetry in medicine arises mainly for the need of non-invasive and highly sensitive discrimination between healthy and tumor tissues. This fast, relatively cheap method may be useful for better histological diagnostics by the physicians. Although, the most challenging goal is to apply tissue polarimetric optical system for in vivo measurements, initially one have to optimize the optical system using ex vivo histological samples, phantoms and etc. This paper is focused on the polarimetric parameters from lower gastrointestinal tract histological samples, by using polarized light with several wavelengths, namely 444 nm, 488 nm, 514 nm, 594 nm and 635 nm, detected and processed by commercially available polarimeter. Our experimental results reveal the best wavelength choice in favor of 635 nm for all colon samples used. Light with circular polarization was used in the experiments, as found to survive more scattering events, compared to linearly polarized light. Furthermore, circularly polarized light carries additional information about the phase difference between the two orthogonal components of the electric field (E_x and E_y) and in the case of reflection, the incident state of polarization undergoes a ip of its helicity. By this way, a better detection of histological changes in tissues, related to abnormal tissue structure can be made. Furthermore, the multiwavelength, polarimetric analysis may provide better insight for future in vivo implementation and the results from the ex vivo biological samples presented in this study, contribute to better discrimination based on optical measurements, applicable for tumor detection.

In the recent study delta-ALA/PpIX is used as fluorescent marker for tumor detection in stomach, small intestine and colon. 5-ALA was administered per os two hours before measurements at dose 20 mg/kg weight. Twenty laboratorial rats with developed neoplasia in gastrointestinal tract were used. Three of them formed control group - without application of exogenous 5-ALA/PpIX, as a contrast fluorescent marker. Their spectral properties were evaluated and used for correction of endogenous sources of fluorescence from stomach and intestine lesions detected. Macroscopic fluorescence spectroscopy parameters of gastrointestinal tissues of the other 17 animals, which were sensitized with 5- ALA?PpIX, were obtained on excitation at 405 nm. Excitation and emission light was delivered by fiberoptic probe 6+1 to the organs investigated in vivo during open surgery procedure on the laboratorial animals used. The fluorescence detected from tumor sites has very complex spectral origins. It consists of autofluorescence, fluorescence from exogenous fluorophores and re-absorption from the chromophores accumulated in the tissue investigated. Spectral features observed during endoscopic investigations could be distinct as the next regions: 450-630 nm region, where tissue autofluorescence is observed; 630-710 nm region, where fluorescence of PpIX is clearly pronounced; 530-580 nm region, where minima in the autofluorescence signal are observed, related to re-absorption of oxy-hemoglobin in this spectral area. The contrast achieved in normal vs. neoplastic gastrointestinal tissues was evaluated. Influence of endogenous 5-ALA/PpIX accumulation was taken into account; as well the role of inflammatory processes on the PpIX distribution and accumulation into the body was evaluated. Dimensionless ratio R=I₆₃₅/I₅₆₀ is evaluated as highly informative one for development of a simple algorithm for differentiation, which could has high diagnostic accuracy for evaluation of tumor vs. inflammatory vs. normal mucosa, using 1-D spectral results. Very good correlation between fluorescence data and histology examination of the lesions investigated was achieved as well.

In our study aluminium–phthalocyanine (AlPc) compounds were applied for exogenous fluorescent diagnostics of adenocarcinoma of stomach in laboratorial animals (male adult rats (n=50)) after application of an experimental model of adenocarcinoma formation with metastasis. The neoplastic lesions were developed under the influence of social stress, as well as chemical stress using nitrosamines during 9 months period of application. Significant fluorescence signal in the region of 670-700 nm was observed in the neoplastic lesions, which absent in the normal mucosa investigated, related to the fluorescence of accumulated in the tumour area phthalocyanines. Autofluorescence background covered region at 450-650 nm with a maximum of 480-520 nm and consists mainly of protein cross-links and co-enzymes - NADH and flavin signals. Endogenous porphyrins fluorescence was also observed in the lesions with a maximum at 630-640 nm. Other organs (liver, small bowel, lungs) were also investigated for a presence of metastases. Histology examination of the lesions was used as a “gold standard” for comparison of the spectral data. Visually, a presence of accumulation sites of AlPc in a form of bright pink patches after excitation at 405 nm was observed, vs. healthy tissue, which remained blue-violet due to autofluorescence signal. Thus allow to use the AlPc fluorescence discrimination not only in spectroscopic mode of detection, but for imaging of the lesions investigated, which is more preferable in the case of clinical applications during endoscopic observations in humans.

Early diagnosis of pulp condition in cases of teeth with trauma is very important not only to preserve the vitality of the pulp but also to prevent both early and late traumatic complications. We investigated 120 frontal teeth with traumas. The teeth were tested on 1-st day, 15-th day, 30-th day, 3-rd month, 6-th month by pulse oximetry (PO) and electric pulp test (EPT). The results we received from pulse oximetry show that the saturation levels immediately after the trauma are very high, reaching 90%. Over the time, there has been a tendency for reduction of saturation, reaching a level of 82% by the 6th month, which is within the limit of the norm. The differences between the obtained saturation levels are statistically significant up to the 30th day of the trauma (p <0.05). The EPT results showed that the highest values were immediately after the trauma - 53 μA. The average values obtained for all periods up to and including 3-rd month are higher than the established norms. They differ statistically between each other and from the values, measured at 6-th month, which are average 8 μA. Comparing the circulatory response and the innervation of the traumatized teeth, we could conclude that the blood circulation recovers more quickly within one month, whereas the nerve conduction is restored until the 6-th month. Thus, the implementation of pulse oximetry in dentistry is of great benefit for the total pulp diagnosis – not only of the nerve, but also of the blood circulation.

In this work, we present fabrication of ZnO nanostructures by pulsed laser deposition in air at atmospheric pressure. The use of this technology leads to formation of nanostructures composed by nanoparticles and nanoaggregates. These nanostructures possess a large surface-to-volume ratio, which makes them suitable for gas-sensor application. The samples were exposed to NH₃ and the effect was investigated of light irradiation on the gas response and recovery time of the sensor element. It was found that the response of the sensor element increases even by irradiation by sunlight. The gas sensing properties of the ZnO nanostructures were compared when irradiated by light of different wavelengths.

This study is focused on the selective laser removal of chlorine-containing corrosion products from artificially corroded samples of copper, brass and steel. Its goal is to find an efficient methodology for laser cleaning of historical metallic objects. The laser treatment is done with two laser sources: Q switched Nd:YAG laser generating nanosecond pulses at 1 Hz repetition rate in the IR (1064 nm) and the green (510.6 nm) spectral range, and copper bromide vapor laser (CuBrVL) generating nanosecond pulses at 20 kHz repetition rate in the green (510.6 nm) spectral range. The cleaning is performed in dry and wet conditions. The surfaces before and after the treatment are characterized using optical microscopy (OM), x-ray fluorescence spectroscopy (XRF), x-ray diffraction spectroscopy (XRD), and laser-induced breakdown spectroscopy (LIBS).

Carbon exists in the form of many allotropes: zero-dimensional sp² fullerenes, the two- dimensional (2D) sp² honeycomb lattice of graphene (parent to graphite and carbon nanotubes), or three-dimensional (3D) sp³ crystals - diamond and lonsdaleite. Carbon can also exist in the form of carbine, a one dimensional (1D) infinite chain of sp¹-hybridized carbon atoms. Each of them has notably different electronic and mechanical properties. Accordingly, it is highly important to correctly identify the hybridization state of carbon for the industrial application of these materials. It is well known that the phase ratio of sp² and sp³ hybridized carbon is distinguishable by X-ray Photoelectron Spectroscopy (XPS) and especially by analysis of C1s lines. Here we report on a thorough XPS study of thin carbon films deposited by pulsed laser deposition (PLD). The studied films consist of a mix of carbon phases deposited on SiO2/(001)Si substrates. The obtained XPS results allows the optimization of PLD process parameters in order to synthesize single to few layered defected graphene/ graphene-like films.

The phase composition and morphology of nano-dispersed carbon phases obtained by nanosecond laser ablation of microcrystalline graphite target immersed in water were investigated. The second (λ_SHG= 532 nm) and the third (λ_THG= 355 nm) harmonics of a Nd:YAG laser system were used to produce different water colloids of carbon. The values of the laser fluence applied for both wavelengths under the experimental conditions chosen were varied from several J/cm² to tens of J/cm² . Raman spectroscopy, X-ray photoelectron spectroscopy and SEM analyses were used to study the carbon target before and after laser treatment and the carbon colloids obtained. The study of the colloids is complemented through X-ray diffraction. A mix of different complex carbon phases and some hydrocarbon polymers (polystyrene predominantly) were found in the colloids.

In this paper we analyze the optical response of azopolymer (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido] -1,2-ethan-ediyl, sodium salt]), shortly denoted as PAZO. The photoinduced birefringence of this material has a potential for polarization holographic recording. We consider thin PAZO layers with embedded TiO₂ spherical particles. This is a numeric simulation motivated by the search of photoinduced birefringence enhancement in azopolymer layers. The scattering of a single particle in the dye-polymer matrix is calculated using the exact vector Maxwell equations. The particles are treated as ensemble of non-aggregated spheres with normal distribution of sizes, characterized by the mean radius <r< and standard deviation σ = <r>/4. Multiple scattering by individual particles is ignored. The refractive index of the PAZO matrix at 442 nm has a complex value (due to absorption) as we have determined it from experimental spectrophotometric data. The 442 nm wavelength is commonly used for recording polarization holographic gratings in azopolymer materials. Embedded TiO₂ spheres with mean radius from 10 to 80 nm are considered. The angular dependences of all the scattering matrix elements, which describe the optical response of the composite layers, are estimated.

We report the fabrication of gas sensor elements by pulsed laser deposition in air at atmospheric pressure. We focused our attention on metal-oxide semiconductors, namely, SnO₂, TiO₂ and MoO₃ and studied the samples’ structure and morphology. The deposition technology applied leads to the formation of nanostructures composed of nanoparticles and nano-aggregates. We report preliminary results on the gas-sensing properties of the metal-oxide nanostructures. The sensors were exposed to CO, acetone and ethanol, with the TiO₂ nanostructure demonstrating the highest response to CO exposure.

This study presents an experimental results of residual stress states in stainless steel plate samples with size 100 x 50 x 10 mm welded using a high-power fiber laser. The technological parameters of the welding process were: laser power Q = 15 kW; laser spot size = 0.65 mm; welding speed V = 3 m/min; 4 m/min; 5 m/min, using 30 L/min of protective Ar gas. The neutron diffraction method was used to determine the residual stresses in the bulk of the material. The neutron experiments were performed on the FSD diffractometer at the IBR-2 pulsed reactor in the Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research - Dubna, Russian Federation. The measured residual stress distributions exhibit maxima at weld seam centers. As expected, for all specimens the residual stress is falling down in regions distant from the weld zone. Maximal residual stress value of 492 MPa was observed for sample welded with speed of V = 5 m/min.

The present work concerns the fabrication and the investigation of Ag nanoparticles, surface embedded in the pulsed laser deposition (PLD) grown ZnO thin films. The third-harmonic Nd:YAG laser is used for PLD of ZnO thin films. The ion implantation technique for Ag doping in ZnO matrix is used. The morphology, texture and composition of the samples are investigated. The Ag distribution in the implanted near-surface region is investigated as a function of the processing conditions. The influence of the substrate temperature and ambient oxygen pressure during the PLD growth of ZnO films is studied. The applied processing parameters during the deposition of ZnO thin films lead to different microstructure of ZnO host matrix and have a significant impact on the properties of subsequently produced Ag/ZnO nanocomposites. The changes of optical surface plasmon resonance (SPR) band of synthesized Ag nanoparticles for different morphologies are analyzed for implanted samples. The composite nanostructures are found to exhibit SPR absorption properties of metal nanoparticles after the ion implantation, especially pronounced for the samples with laser grown ZnO matrix at high substrate temperatures. This study demonstrates how the different crystal structure of the ZnO supporting material, influences the Ag implantation process and, respectively, the properties of the produced Ag/ZnO nanocomposites.

In this work results on laser assisted formation of silver nanoparticles in glass are presented. The sample material used in the experiments is Ag doped borosilicate glass fabricated by conventional melt quenching method. The glass samples are irradiated by nanosecond laser pulses at wavelength of 266 nm with a wide range of fluences and number of applied pulses. It is found that the laser radiation can lead to specific yellow coloration of the irradiated areas. The performed analyses show formation of silver nanoparticles in these zones. The optical properties of the irradiated areas are found to depend on the laser processing parameters and the silver concentration. The mechanism of nanoparticle formation is also discussed. The presented method can be used for formation of nanoparticles inside transparent materials and can be used for fabrication of novel materials with application in photonics.

Mixtures of micron to submicron complex carbon phases, namely, defective graphene, graphene-like (multi-layered graphene, graphene oxide etc.), graphite flakes etc. as fine suspensions were obtained by pulsed laser ablation of highly purified microcrystalline graphite targets immersed in double distilled water. The fundamental wavelength (λ = 1064 nm) and the fourth harmonic (λ_FHG = 266 nm) of a Nd:YAG laser system (15 ns pulse duration, 10 Hz pulse repetition rate) were used in the fabrication process. The laser fluence value corresponding to the onset of the ablation process, the one initiating optical breakdown in water and an intermediate value were used for each of the wavelengths mentioned above. The morphology of the particles dispersed in water was studied by scanning electron microscopy (SEM). Their phase composition and structure were explored by Raman spectroscopy. It showed the presence of some traces of polymerized hydrocarbons (polystyrene, polybutadiene etc.) in addition to the main carbon phases: defected graphene, reduced graphene oxide and graphite.

The paper presents results on nanosecond laser ablation of ZnO nanostructures immersed in a liquid. The nanostructured ZnO samples were prepared in two steps. In the first one, a thin catalyst Au layer was deposited on the glass substrate by standard on-axis pulsed laser deposition (PLD) technique. In the next step, using again the PLD method, ZnO was deposited on the Au layer and thus the nanostructured ZnO samples were produced. The as-prepared samples were then immersed in double distilled water and irradiated by nanosecond laser pulses delivered by a Nd: YAG laser system at λ = 532 nm. Two different configurations of irradiation – against the structure and through the glass substrate – were used in the ablation in liquid experiments. The influence of the laser fluence for each of the ablation configurations used on the size, shape and optical properties of the obtained colloidal nanostructures was investigated. It was established optimal processing conditions, allowing transfer of the ZnO nanostructures from the substrate into the liquid medium. The nanostructures shape and size distribution were evaluated by means of transmission electron microscopy. Selected area electron diffraction was employed for chemical phase identification of the produced nanostructures. The colloids obtained were investigated by optical transmission spectroscopy in the near UV and in the visible region.

This paper presents a method for fabrication of oriented multicomponent nanowires composed by nanoparticles. The technology is based on nanosecond pulsed laser deposition of mixed target in the presence of an external magnetic field. The targets used for the ablation process consist of Fe₂O₃ and Ag₂O with different ratio between them. The laser ablation is implemented in air at atmospheric pressure by using Nd:YAG laser system operated at 1064 nm. SEM analysis of the surface of the as-deposited samples reveals a presence of micrometric nanowires which are predominantly oriented in the direction of the magnetic field. These nanowires are composed by arranged nanoparticles formed in the plasma plume. The influence is investigated of the Fe₂O₃/Ag₂O ratio in the target on the morphology and optical properties of the structures. Surface plasmon resonance band of Ag nanoparticles was observed in the transmission spectra of the samples with the highest Ag content. The material composition of the samples was identified by EDX and XRD analyzes. The obtained structures can find application in the fields of nanoelectronics, spintronics, magneto-optics and plasmonics.

The fabrication of nano-crystalline carbon films was implemented by the application of pulsed laser deposition (PLD) technology. The experiments were performed in a standard on-axis laser ablation (LA) configuration. The third harmonic of a Nd:YAG laser was used for ablation of a microcrystalline graphite target. All experiments were performed in vacuum at a pressure of 1×10^-3 Pa for different deposition times. (001) Oriented silicon (Si) covered by either 350 or 450 nm silica (SiO₂) layer was used as a substrate. The films have a thickness between 4 and 40 nm and are characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM) and ellipsometry measurements. We established deposition of nano-sized graphene-like films on top of predominantly amorphous carbon films with a thickness of 1- 2 nm. The measured the (n and k) and determined the values for the forbidden gap of the films which are between 0.01 eV and about 1 eV with reference to the sp³ hybridized carbon content of the film.

The fluorescence spectra of Bulgarian and French wines of the same price class were obtained at excitation wavelengths of 265 nm, 275 nm and 295 nm. The excitation-emission matrices are obtained and compared. A correlation between the emission maxima and the anthocyanins or the antioxidant activity expressed in Trollox units is obtained.

The isotropic Maxwell-Boltzmann (M-B) velocity distribution is the accepted standard for a gas at thermal equilibrium, with the Doppler width considered to deliver a very precise measurement of the temperature. Nevertheless, the physical nature of the surface, and the atom-surface interaction, in its long-range (van der Waals type) regime as well as in its short-range regime leading to adsorption/desorption mechanisms, are far from the ideal situation describing the foundation of gas kinetics. Through the development of vapor spectroscopy at an interface, a high sensitivity to atoms flying nearly parallel to the gas interface is obtained, and deviations to M-B distribution could have observable effects, even affecting the ultimate limits to resolution. We report here on the development of an experiment involving a dedicated set-up of spatially-separated pump-probe experiment in a narrow cell. A first series of investigation could not evidence a deviation for Cs atom velocities at a nearly grazing incidence (typically 1.5 -5°). We discuss various technical improvements to increase the sensitivity to atoms flying parallel to the surface, along with specific spectroscopic information that may be collected. Alternately, the comparison of standard selective reflection spectroscopy with simultaneous volume spectroscopy may be a source of complementary information. At last, we discuss how the Boltzmann energy distribution, among molecular or atomic levels, may become sensitive to specific thermal exchanges at the surface, in an equilibrium situation.

Dark matter (DM) represents one of the most intriguing challenges of modern physics, both for the theoretical predictions and for the experimental setups. The search for the possible DM component candidates regards a wide range of objects and of energy values. In order to detect processes related to very weak interactions, as expected in these cases, it is necessary to improve the performances of the available detectors making them more efficient in terms of energy threshold and mass. Here we present a research activity aimed at the development of a novel type of detector based on laser interrogation of atomic energy levels for species that have been loaded in a solid matrix of a non interacting material at very low temperatures. The laser assisted transitions are only promoted when an incident particle is absorbed in the material, releasing its energy to the embedded atoms. The detection can be obtained via both optical and electronic methods.

We present a brief overview of the current state of the experimental research on the development of the element base of quantum computers with qubits based on single neutral atoms trapped in optical traps. The discussion focuses on the requirements for qubits, peculiarities of single neutral atoms as qubits, methods for the quantum register development and for the implementation of single-qubit quantum logic operations in the laser and microwave fields, and two-qubit operations through the dipole–dipole interaction after a short laser excitation of atoms to the Rydberg states. The results of the experiments on the observation of the interaction of two and three Rydberg atoms by a Förster resonance controlled by dc and radio-frequency electric field are presented.

In this communication, we demonstrate a new use of the micrometric (700 μm) thick, high-quality optical cell filled with Cs vapor that intrinsically contains extremely small concentration of Rb atoms. When heated to temperature about 200 °C such alkali mixture consists of Cs₂ dimers and Cs atoms together with very small number of Rb atoms. We use the Rb atomic spectrum as a reference one, in order to measure spectral profiles and frequency positions of the observed spectral lines of Cs₂ molecules within the B¹П_u←X¹Σ_g⁺ absorption band in the spectral region around the D₂ resonance line of Rb with wavelength λ = 780.24 nm.

We report on the investigation of narrow sub-Doppler-width resonances observed at the D₂ line of Cs atoms (F_g = 4 → F_e = 3, 4, 5 hyperfine transitions), confined in thin optical cells. These cells have a thickness of L = 6λ (λ = 852 nm) and L = 700 μm, and are irradiated by two narrow-band laser radiations (one with fixed and the other with scanned frequency). We show that for zero frequency detuning of the fixed-frequency laser from the F_g = 4 → F_e = 5 hyperfine transition, its absorption spectrum in the thin cell consists of resonances, centered at the respective hyperfine transitions. The spectral widths of these resonances range from 2 to 20 MHz, and they are characterized by a good contrast and extremely small Doppler background. This spectrum is highly sensitive to the frequency offset of the fixedfrequency laser. The analysis leads to the conclusion that the spatial restriction of Cs vapor suppresses the interaction of the light with atoms with significant velocity component along the direction of the laser beam propagation.

Significant modification of the spectrum of the D1 line of ⁸⁵Rb in optical cells with high quality antirelaxation coating on the walls is studied experimentally and theoretically analyzed. The spectral profiles of hyperfine transitions are found to be significantly dependent on the velocity and the direction of the laser frequency scanning. A physical explanation is proposed for the observed features, which is confirmed by numerical simulations. The effect of small magnetic field on hyperfine spectrum is also discussed.

We report some preliminary results on experimental investigation of the potential of Light Induced Atomic Desorption (LIAD) applications for density control in antirelaxation coated cells and coherent spectroscopy. LIAD is a non-thermal process whereby atoms adsorbed on a surface are released under illumination. It is applied mostly to implementing optical atomic dispensers in the cases when high atomic density at low temperature is needed - for example, for loading atomic devices as atomic magnetometers, atomic clocks, atomic traps and their miniaturization. An advantage of the light control is that it is faster than the temperature control. More than an order of increase of the density with LIAD is obtained. Some peculiarities in the 780 nm absorption and fluorescence spectra registered in dense Rb vapor are registered. The absorption and fluorescence spectra in Rb vapors controlled by temperature and LIAD are compared.

Observation of speed of processes by dynamic speckle metrology has been applied to different samples of industrial or biological nature. The method allows for detecting regions of lower or higher activity on the sample surface through statistical processing of the speckle patterns formed on this surface under laser illumination. The aim of the paper is to check applicability of this dynamic speckle technique for monitoring of the drying process in polymer water and methanol solutions. For the purpose, we recorded several sets of 256 correlated in time speckle patterns of a transparent drop of PAZO water solution and PAZO methanol solution on a glass plate illuminated by a He-Ne laser. The sets were separated by intervals of several minutes, and the last set was recorded 100 minutes after the start of the experiment. For statistical description of activity on the observed sample we applied pointwise correlation-based algorithms to binary patterns formed by comparison of intensities at each point to a sign threshold. The obtained two-dimensional maps of the used statistical estimator at different time lags clearly indicated the difference between water and methanol solutions and proved efficiency of dynamic speckle analysis for monitoring of drying processes in polymer solutions.

Dispersion properties of photonic crystal fibers, important in many applications might differ from the desired specifications due to deficiencies in the manufacturing process, thus an experimental verification is indicated. In this paper the possibility of measuring the birefringence of a polarization-maintaining photonic crystal fiber by using an interferometric-spectral technique is demonstrated. The polarization-preserving photonic crystal fibres used belong to different manufacturers and exhibit high birefringence values, ranging from 5.7x10^-4 to 6.7x10^-4, when operating in the vicinity of 1550 nm. Different Sagnac interferometers were made with loops of polarization preserving fibres having different values of birefringence and length L, consequently producing diverse spectra of transmittance. A high precision optical spectrum analyzer was applied for spectral data recording, allowing to calculate the properties associated to each scheme of birefringence photonic crystal fibre. In our case, the experimentally measured values fell within the value ranges given by the manufacturers.

The sciences of physics and quantum electronics are currently in the beginning of the second quantum revolution. If the main goal of the first quantum revolution can be formulated as the understanding of our physical world and its atomic and nuclear structures, today, during the second quantum revolution, we are able not only explain the Nature, but we are actively applying our understanding of the quantum world, for example, to create new artificial atoms (quantum dots) and develop new technologies and nanoscale quantum electronic devices based on the quantum dot (QD) arrays like QD lasers, QD memories, and quantum-dot cellular automata. The main objective of our work is to demonstrate that nanoscale cold electron emission schemes may offer an intriguing new technical methodology for compact fast vibration sensors. We propose an electronic displacement device by positioning a vibrating anode toward a special field electron emitter. Cold field electron emission from an array of quantum dots grown on SiC is applied, where the distance between the tip of emitting mounds and the counter-electrode (anode) is controlled by the moving object under study. To that end, field emission electron sources are built on a flexible substrate, which can take up and transfer the oscillations of a vibrating moving system into a change of the spacing distance between emitter and anode, and by this modulate the emission current density. As is derived from Fowler-Nordheim equations, sensitivity down to a few nanometers of vibration amplitude is possible. In conclusion, we compare our vibration detection scheme based on the quantum dot array with modern micro- and nano-photonic and laser-based devices.

The method of combined lidar and radiometer sounding (LRS) became a specialized tool for measuring altitude distributions of aerosol optical parameters and aerosol mode concentrations. The work gives description of advanced version of LRS technique, which integrates data of ground-based multiwavelength lidar systems, as well as satellite lidars like CALIOP, with data of AERONET radiometer stations for monitoring aerosol mode concentration profiles to study the atmospheric process over the area of large regions, or the Earth's atmosphere as a whole. Lidar and Radiometer Inversion Cod (LIRIC) is used as a base software package for processing data of terrestrial and satellite lidar observation because of high stability of its sequential inversion procedure for processing combined radiometer and lidar data. Special software module was developed to extract the ensemble of individual CALIOP profiles of attenuated backscatters in the vicinity of AERONET sites from CALIPSO Lidar L1B Profile Data. A number of collocated measurements by means of AERONET radiometer, ground-based lidar and CALIOP were carried out to validate the results of the extended LRS technique. Altitude profiles of aerosol mode concentrations retrieved from ground-based and satellite lidar data are compared to estimate differences between two types of LRSmeasurements. Advanced terrestrial and satellite LRS technique was used to obtain the “snapshot” of aerosol concentration profiles over the world in the frame of international “Lidar and Radiometer measurement campaign - 2017" (LRMC-2017). Thirty nine combined lidar and radiometer stations in Eurasian and South American continents participated in terrestrial part of the campaign.

This article summarizes representative examples of elastic backscatter lidar observations in Planetary Boundary Layer (PBL) and in troposphere. The measurement objectives are the diurnal variation of the PBL stratification and cases of long-range transport of aerosol in the troposphere. Two lidars setups are used in the presented measurements. One is the traditional one, based on laser with low-repetition rate and high pulse energy, while the other setup is based on micropulse laser with high pulse repetition rate. Both lidars provide highly satisfactory results, each in its optimal measurement altitudes. The presented examples for aerosol transport include cases for Sahara dust and volcano ash. The transport studies are supported with back-trajectory analysis. The PBL studies include verification of the generally accepted processing methods for aerosol stratification determination, as well as example of diurnal development. The diurnal development of the PBL, determined by the backscatter lidar is supported with measurements with standard meteorological instruments.

We report on lidar detection and characterization of Saharan dust in the atmosphere above Sofia, Bulgaria, during the months of February in the years 2017 and 2018. Presented are results of aerosol measurements performed by using twochannel lidar based on a frequency-doubled pulsed Nd:YAG laser emitting at 1064 nm and 532 nm. We studied and characterized optical, geometrical, and dynamical properties of the registered aerosol fields. Vertical profiles of the atmospheric backscatter coefficient and color-coded diagrams in height-time coordinates based on range-corrected lidar signals are obtained in order to analyze the aerosol/dust layer density distribution and dynamics. Based on the retrieved backscatter profiles at the two lidar wavelengths, the corresponding vertical profiles of the backscatter-related Ǻngström exponents were calculated in order to characterize qualitatively the dominant particle-size fractions in the aerosol/dust layers observed. The lidar results obtained were combined with air-transport modelling and forecasting data in order to derive conclusions concerning the aerosol’s origin and type. It is shown that on the days of lidar observations meteorological conditions in Sofia region, as well as the vertical structure and aerosol composition of the near surface atmospheric layers, have been significantly influenced by the Saharan dust intrusions. Analyzing the aerosol Ångström exponent, an anomalous height distribution of the dust particle size fractions is ascertained and discussed. The results obtained confirm the tendency of increasing frequency of transporting considerable amounts of warm air masses from North Africa to Europe during the winter, indicating seasonal deviations in the air-intercontinental circulation systems. They also illustrate the potential of using lidar approaches to help monitor ongoing processes of local, regional, and global climate changes.

Mineral dust and cirrus clouds are recognized to be among the major modulators of the atmospheric energy budget. Sahara Desert is the Earth’s largest source of mineral dust of natural origin. Saharan dust intrusions in the atmosphere over Europe are frequently accompanied by a parallel occurrence of cirrus clouds. Studies on the vertical aerosol distribution in such cases are important in providing a better understanding of the radiative effects of aerosols and clouds, and for the development of more accurate climate models. Lidars are considered as one of the leading techniques for conducting such studies, due to their high range/time resolution and sensitivity to optically-thin aerosol layers and clouds. In this work, we present results of lidar observations of the simultaneous presence of Saharan dust layers and cirrus clouds in the troposphere, with regard to their possible interaction, particularly in cases when the Saharan dust particles act as nuclei in cirrus cloud formation. Accordingly, experimental data derived from the regular long-term lidar investigations of Saharan dust loadings above Sofia, Bulgaria, are described and analyzed. The aerosol measurements were carried out by an elastic-backscatter lidar based on a frequency-doubled Nd:YAG laser. The experimental results are presented as color maps of the aerosol density distribution dynamics and by time-averaged vertical profiles of the aerosol backscatter coefficient. The process of cirrus cloud nucleation on desert dust particles is detected and analyzed in its development and evolution.

In this work some features are revealed, simultaneously by LIDAR and contact facilities, of the aerosol pollutions near high-traffic sites in Sofia City. Such features of interest are the extinction coefficient of the aerosol ensembles and their mass concentration, as well as the shapes and sizes and the structure of the aerosol particles and their chemical composition and biological content. They outline possible negative effects of the aerosol pollutants on the human health. The experiments are conducted in the spring and summer, in different sites of interest in Sofia City. The results about the aerosol mass concentration-to-extinction calibration of the LIDAR constant, obtained in the spring and in the late spring and the summer, are consistent with each other and with the combined spring-and-summer result. Using electron microscopy, various aerosol samples are visualized resembling mineral dust particles, pollen, soot, and even microorganisms. The results from the analysis of the images obtained would serve as guidelines of further chemical and microbiological studies.

Differential absorption lidar (DIAL) feasible to detect methane is developed on a pair of powerful pulsed (10μJ) laser diodes emitting on 1,56μm -1,66μm wavelengths. Methane is a potent greenhouse gas that is responsible for the present enhancement of the greenhouse effect. The spectral range of wavelengths utilized by the laser diodes matches an intensive second overtone of the methane molecule pure of interfering spectra of the other major atmospheric gases. Spectroscopic applications of the powerful laser diodes were generally limited by their broad laser line. Though spectrally unresolved, multiple resonance absorption lines modulate the laser radiation propagating in the atmosphere. The intensity of integral absorption is assessed combining the linestrengths taken from HITRAN database with the laser spectral line. The resultant absorption spectrum is immune to pressure variation, while the dependence on temperature is found to be within 10% error. The reported DIAL technique utilizes the advantage of simple operation within lidar ranges of 0.5- 5km prospective for reconnaissance of atmospheric methane and climatic monitoring.

Mineral aerosols from Sahara desert are frequently transported to Europe by regional or trans-continental air circulations. During such a long-range transport, Saharan dust is naturally mixed with other aerosols. The pathway of desert aerosols frequently passes over the Mediterranean Sea or the Atlantic Ocean. Under certain conditions, dust particles can blend with marine aerosols to form a mixture with specific volume/mass concentration and particle size distribution. These parameters are determinative for the climatologic, ecologic and medical impacts of the aerosols. Therefore, studies of desert-marine aerosols’ interacting and mixing are of considerable scientific and practical importance.

In this work, we report results of lidar measurements and analysis of Saharan dust layers observed over Sofia, Bulgaria, possibly containing considerable amounts of marine aerosols captured and mixed with the dust particulate matter during the passage of air masses close to the surface of the Mediterranean Sea and/or Atlantic Ocean. The aerosol layer’s origin is proven by using air mass transport modeling and forecasting data. Measurements are carried out at two wavelengths (1064 nm and 532 nm) by means of the two aerosol channels of a lidar based on a frequency-doubled Nd:YAG laser. Topological, dynamical, optical, and microphysical properties of the dust/aerosol layers are studied and analyzed. Timeaveraged vertical profiles of the atmospheric backscattering coefficient at 1064 nm and 532 nm are presented. By using backscatter-related Ångström exponents, microphysical properties of aerosol particles are characterized qualitatively. Color map diagrams illustrate the temporal evolution of the aerosol density height distribution. Conclusions concerning the effects of dust mixing with marine aerosols are drawn.

In the present work, Poisson-fluctuating lidar profiles are modeled statistically as obtained from clear and hazy atmospheres containing Sharan-dust-like layers. The shot-noise fluctuations are simulated in fact induced by the useful signal itself, the optical background, and the dark current in the photon detector. The profiles obtained for UV, VIS and NIR sensing radiations are compared and analyzed. It is shown that the best lidar images of Saharan dust layers are obtainable by using NIR sensing radiation. They are characterized by higher contrast and clarity. The images obtained by using UV or VIS radiation may be entirely masked by shot-noise and even by multiple-scattering due parasitic (bias and random) noise. To clarify the images obtained in this case, by lowering the random noise level, one should average, as shown, the lidar profiles over a series of laser shots and/or smooth them along the lidar line of sight. Certainly, this lowers the temporal and/or spatial resolution of sensing by UV and VIS radiation. Thus, the results obtained confirm and illustrate the advantages of the NIR wavelength range, when sensing dense compact aerosol objects, predicted previously by the mean profiles investigated of the lidar signal strength and signal-to-noise ratio.

The foundations of quantum approach to describe of distortion and delay of GPS signal passing through the D and E atmosphere layers are proposed. The problem is reduced to resonant scattering of photons, moving in electromagnetic field produced by the transmitter, on the Rydberg complexes formed in the two-temperature non-equilibrium plasma. The following two processes are considered. First process leads to a forming the creation of additional photons due to stimulated emission and direct increase in the power of the received signal. The second one provides a shift the carrier frequency signal and time delay of its propagation. It happens due to the resonant scattering of Rydberg electron on the ion core and molecule of neutral medium in the intermediate autoionization states due to the non-adiabatic coupling of electronic and nuclear motions. The purpose of our message is to determine the connection of resulting frequency shift and delay time of the satellite signal with the quantum dynamics inside the Rydberg complex consisting of a highly excited molecule and molecule of neutral medium. We note that in one act of resonant photon scattering, the delay time in the intermediate state of the complex is 10^-10 s, i.e. they are peculiar traps for the GPS signals. Under normal geomagnetic conditions the total delay time of the signal arriving at the receiver is Δτ ~ 10^-7 s. Next factor to be taken into account is the additional background incoherent microwave radiation from Rydberg complexes leading to an increase in the signal/noise ratio.

Compact optical sources of radiation with high average power are needed for many applications from sensing to imaging and spectroscopy. The control of non-linear effects during the propagation of intense ultra-short laser pulses in various gas allows the generation of novel very intense radiation beams which can be used for sensing and imaging. We discussed non-linear effects during ultrafast laser beam propagation in two very different interaction regimes, long distance propagation in ambient air and short distance propagation at very high intensity and in high density gas, obtained with high peak and high average power laser systems.

We review the Tappert transformation for the nonlinear Schrödinger equation and generalize it for the higher- order nonlinear Schrödinger equation (hoNLSE) model of femtosecond nonlinear optics, in which the para- meterized gravitational-like potential e¤ectively simulates the Raman self-scattering e¤ect (the soliton Raman self-frequency shift). We present the explicit gauge transformation of this model into the "free" hoNSLSE with varying in time dispersion and nonlinearity, but without external potentials. With a certain choice of the dispersion and nonlinearity parameters, hoNLSE is turning into the completely integrable physical models, for example, the Hirota equation with gravitational-like potential, for which the same reversible gauge transformation and the change of variables are fulfilled. The transformations between the proposed integrable models allowed one to obtain directly the soliton solutions of the forced nonisospectral equations - accelerating in the gravitational- like potential nonautonomous solitons - without resolving the nonisospectral IST problem with varying in time spectral parameter.

In recent experiments in air with femtosecond pulses significant depolarization effects in nonlinear regime were observed. We use the generalized cubic type nonlinearity and investigate how this operator influences the vector field polarization. A vector set of nonlinear differential equations describing the evolution of the main and signal is derived. The polarization properties of the components of vector fields are investigated numerically.

The problem with generating of new frequencies (signal and idler waves) in parametric four-photon processes without including the Raman scatter was solved only in approximation for a constant electric field or a constant intensity of the pump wave. The overall task which includes the change in intensity and the phase of the pump wave has not been studied in detail in the literature up to now. The main idea of present work is to solve the more general problem in which we have energy exchange between pump wave, signal and idler waves.

Different kind of vortex structures of laser beam can be created by optical holograms and different optical masks. In the theory these vortices are solutions of the 2D scalar Leontovich equations. These solutions admit amplitude and phase singularities.

The main tack of this work is to investigate the possibility of formation of vortex structures for narrow-band optical pulses, propagating in Kerr-type media. The evolution of such type of laser pulses is governed by nonlinear vector system of amplitude equations in second approximation of the linear dispersion. We found new class of analytical solutions with vortex structures. The nonlinear dispersion relations obtained by these vortex solutions show that their stability is due not only to balance between diffraction and nonlinearity, but also to a balance between non-linearity and angular distribution.

Optical vortices (OVs) are the only known truly two-dimensional phase dislocations. Because of their spiral phase fronts, the OV interaction results, in the simplest case (when two OVs are presented), in vortex mutual attraction/repulsion or in OV pair rotation. In this work we provide experimental evidences that a stable elementary cell forming the base for a large optical vortex lattice can be created by situating equally and singly charged OVs in the apices of a triangle and square and by nesting an additional control OV with an opposite unit charge in the center of the structure. Experimental data for the rotation of these triangular and quadratic elementary cells vs. OV-to-OV separation as well as the rotation of the same structures vs. propagation distance are presented. Generation and stable propagation of large rigid square-shaped and hexagonal OV lattices is demonstrated.

The photo-excited luminescence response of solutions (in organic solvent) of eight selected organometallic coordination complexes of Iridium Ir(III) ion is studied upon irradiation with high-intensity short-pulse (nanosecond) ultraviolet laser irradiation, as well as by ultra-high-intensity ultrashort (femtosecond) laser pulses in the visible (violet). The Ir-complexes are cyclometalated and contain bis-phenylbenzothiazole as a main ligands and auxiliary β-diketone ligands, and they are intended to be used as luminescent materials and sensitive nanoprobes, e.g., in organic optoelectronics, sensorics, mechatronics and laser fluorescent microscopy. The results obtained by laser spectroscopy of dilute (10^–5 M) solutions of the examined Ir-complexes show that they are efficient triplet emitters whose photo-excited emission is proper for fluorometric, optoelectronic and photonic applications.

Interference Wedged Structure (IWS) is an optical element with useful properties for optical metrology, spectral analysis and optical communications. We have introduced in the paper a new perspective element of this type – Composite Tunable Interference Wedged Structure (CTIWS). The CTIWS is list-like sequence of superimposed wedged layers each with reflecting surfaces. For conveniently chosen apex angles and thicknesses of the layers, the CTIWS can assure high spectral selectivity to 0.01nm within a spectral range of 10 nm and more at smooth tunability by simple sliding of the structure along the wedge arm (a few cm). We have developed simple physical description of the IWS and CTIWS by adapting Fabry-Perot theory. We show that for the most important practical cases the results are similar to the obtained by more complex exact analytical description. The theoretical predictions are confirmed by experimental results. On the base of IWS and CTIWS combined in a suitable architecture, we have introduced and studied a new lossless Wavelength Division Multiplexing (WDM) element with independent tuning of each output/input. We considered the WDM implementation for the case of fiber optical systems used in optical communications.

Based on our experience in the field of the interferential wedge, we present a new competitive application of such optical elements and structures built from them with theoretical description and experimental verification. We have demonstrated that a conventional interferential wedge or a structure of two wedges in compact layered implementation can be used as an attractive simple light power splitting element for a spatially and spectrally narrow light beam (basically a laser beam). The element can provide: 1) precisely and variably controlled ratio of the reflected and transmitted power by simple sliding in its plane of the list-like wedged structure with an apex angle of ~10^-5 rad; 2) division practically without energy losses; 3) power ratio control without causing change of propagation direction of the reflected and the transmitted beams that is of essential interest for applications in optical schemes with complex geometry of the beams propagation; no optical properties variation of the reflective layers (mirrors) during the sliding; 4) working at beam power densities of MW/cm² - GW /cm² when the optical element is built from optical materials (layers) with high light damage resistivity.

In this paper we demonstrate flexible polymer dispersed liquid crystal (PDLC) devices using graphene as transparent conductive electrodes on polyethylene terephthalate (PET) substrate. Graphene was grown by Low Pressure Chemical Vapor Deposition (LPCVD) technique and characterized by Raman analysis, optical and electrical measurements. Several graphene-based PDLC devices have been fabricated and their electro-optical characteristics, response time and bending ability were measured and discussed. The results support the graphene promising features for integration in flexible optoelectronics.

Properties of polymeric materials are essential for their application in optical design. Refractive indices of different optical polymers are presented in the temperature diapason 10-50 °C. Dispersion is evaluated by the Abbe number at the measuring temperature. Some additional optical parameters for application in fiber optics are given. Mechanical properties of plastics are important in optical design, too. Dynamic elastic moduli of studied polymers are determined on base of ultrasonic measurements. Optomechanical, thermo-optical and thermo-mechanical parameters are presented. Application of polymeric materials in laser optical systems is illustrated by the designed all-plastic mirror objective which may be used in a lidar equipment for atmospheric pollution monitoring. Geometrical aberrations are computed.

Random lasers are a novel disorder-based laser light source with many photonics applications. In the present work we study the optical properties of a new unordered medium consisted of an epoxy resin as matrix with dissolved different binary solutions of Rhodamine 6G and Rhodamine B. The choice of these dyes is related to their great application in laser physics. A detailed study of the spectral dependence of fluorescence is performed. The spontaneous emission is very intensive and follows the spectral dependence of dyes transmission and exceeds 750 nm. The threshold of the laser medium is 1.6 mJ for 10 ns pulse at second harmonics of Nd:YAG laser, and full width at half maximum (FWHM) is around 1.5 nm. Slope efficiency of the medium is 16%. The laser generation without resonator was studied also and lasing emission at 597 nm was observed. The fact can be explained by random lasing provided by the medium. This is in good relation and in accordance with the intensive scattering inherent to the medium which is registered. Not used additional scatter centers such as ZnO nanorods or Ag, Al, Al₂O₃, TiO₂ agglomerates and others in our experiments.

High-beam-quality laser oscillation is obtained at two Sr⁺ and several Sr atom lines in the middle infrared spectral region with average output power of about 4 W in a sealed-off laser tube. Using the same laser tube construction and enhancing the active volume in bore and length, average output power of about 10 W is also achieved. Based on these laser tubes, master oscillator–powerful amplifier laser system, in which low-power high-beam-quality laser radiation from the oscillator is amplified to the required level of the energy laser parameters, is also developed and investigated.