This PDF file contains the front matter associated with SPIE Proceedings Volume 9893, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

We report on the generation of picosecond deep ultraviolet pulses at 257.5 nm and 206 nm produced as the fourth and fifth harmonic frequencies of the diode-pumped Yb:YAG thin-disk laser at the fundamental wavelength of 1030 nm. We present a proposal for a picosecond pulse mid-IR source tunable between 2 and 3 μm. The laser at the fundamental wavelength is based on a chirped-pulse amplification of pulses of a sub-ps laser oscillator in a regenerative amplifier with a thin-disk active medium. The diode pumping at the zero phonon line is used. The output beam is close to the fundamental spatial mode and the pulses are characterized by a 100 kHz repetition frequency, less than 4 ps pulse duration and ≤1 mJ pulse energy. The fundamental beam is split and the main part is first frequency doubled in an LBO crystal. Subsequently the fourth harmonic frequency (257.5 nm) is produced by frequency doubling of the second harmonic frequency in BBO/CLBO crystals. The remaining part of the fundamental beam is summed with the fourth harmonic beam in the 1ω+4ω quantum reaction in a further CLBO crystal for the fifth harmonic frequency (206 nm) production. The design for the generation of the mid-IR wavelengths is based on the optical parametric generation and amplification. The first stage contains a temperature tuned PPLN, the following amplification stages are based on KTA crystals tuned by angle. Picosecond output pulses tunable between 2 and 3 μm at an average power of 10 W are proposed.

Laser sources with light-emission in the yellow spectral range around 577nm are very favorable for a variety of applications. These include applications in astronomy, in ophthalmology or in quantum optics. The generation and amplification of 1154 nm light is not straight forward when using Yb-doped optical fibers, since lasing occurs preferentially around the gain-maximum of 1030 nm. We generate the radiation within a fiber Bragg grating (FBG) based cavity and focused on reducing the amplified spontaneous emission (ASE). After the cavity, the output is frequency doubled to 577nm by using a second harmonic crystal.

We introduce the topic of short-pulse laser damage in optical coatings in order to understand the intrinsic limitations depending on the application, and the possibility of laser damage resistance improvement. Firstly we describe the physical process of a high intensity femtosecond laser pulse interaction with an optical coating and how this interaction can lead to a damage of the film. Then we present the main facts about laser damage resistance of coatings that are relevant for applications and related to the previously described processes: the dependence of the Laser-Induced Damage Threshold (LIDT) of coating materials with bandgap, the decrease of LIDT with the pulse number, the wavelength and pulse duration dependence, etc... We also discuss on the question of the role of macroscopic defects on damage initiation in this regime and damage growth under multiple irradiation. Eventually different strategies to improve the laser damage resistance will be discussed: engineering of the electric field distribution in the stack, fabrication of mixture materials with enhanced LIDT, mitigation of defects.

We report on development of a 100-kHz, 5-mJ picosecond system based on a two-stage thin-disk Yb:YAG regenerative amplifier. With a compact ring cavity, we obtained 565 W with 46.7% optical-to-optical efficiency in continuous-wave. In seeded operation, pulses with energy up to 4 mJ and 1.4-nm bandwidth were generated with 39% extraction efficiency. Pulse compression below 2 ps was so far demonstrated at lower pulse energy of 1 mJ. Full-power pulse compression and further pulse energy increase are under development.

In this paper we review the development of high energy, nanosecond pulsed diode-pumped solid state lasers within the Central Laser Facility (CLF) based on cryogenic gas cooled multi-slab ceramic Yb:YAG amplifier technology. To date two 10J-scale systems, the DiPOLE prototype amplifier and an improved DIPOLE10 system, have been developed, and most recently a larger scale system, DiPOLE100, designed to produce 100 J pulses at up to 10 Hz. These systems have demonstrated amplification of 10 ns duration pulses at 1030 nm to energies in excess of 10 J at 10 Hz pulse repetition rate, and over 100 J at 1 Hz, with optical-to-optical conversion efficiencies of up to 27%. We present an overview of the cryo-amplifier concept and compare the design features of these three systems, including details of the amplifier designs, gain media, diode pump lasers and the cryogenic gas cooling systems. The most recent performance results from the three systems are presented along with future plans for high energy DPSSL development within the CLF.

Fe:Zn(1-x)Mn(x)Se solid solution spectroscopic and laser properties were investigated in the temperature range 80- 290 K. Two novel samples with different zinc - manganese (Zn–Mn) ratio described by the Mn content x (0.1 or 0.2) were used and the results were compared to the known Fe:ZnSe crystal. The samples had a broad absorption spectra with the maximum around 3 μm and therefore an Er:YAG laser (2.94 μm, 10 mJ, 120 ns) was used as a pump radiation source. The Fe:ZnMnSe fluorescence spectra are generally broad in the range 3.5 – 5.5 μm. In the case of Fe:ZnMnSe x = 0.1, the fluorescence spectrum at 290 K is ranging from 3.5 to 5.5 μm. Lowering the temperature down to 80 K lead to the spectral narrowing mainly in the mid-IR part, but the fluorescence is still up to 5 μm at 80 K. In the case of Fe:ZnMnSe x = 0.2 the fluorescence is shifted towards mid-IR up to 5.2 μm even at 80 K. The fluorescence lifetime decreases from tens of us at 80 K down to 1 us at 240 K. The laser oscillations were successfully achieved with both novel Fe:ZnMnSe crystals in the temperature range 80- 290 K. In the case of x = 0.1, the central wavelength was ~4.2 μm at 80 K and the temperature increase up to 290 K led to almost linear increase of the wavelength up to ~4.75 μm. The tendency was similar in the case of Fe:ZnMnSe x = 0.2: the output wavelength increased from ~4.3 μm up to ~4.8 μm with the temperature increase from 80 to 290 K. The laser spectral linewidth was about 300 nm. In comparison with the Fe:ZnSe crystal, the laser output wavelength shift toward mid-IR region without any spectrally tunable element in the laser cavity can be clearly observed.

In this work, a passively mode-locked Yb:YGAG (Yb:Y₃Ga₂Al₃O₁₂) ceramic laser generating picosecond pulses at liquid-nitrogen temperature is demonstrated. The Yb:YGAG has a similar structure to Yb:YAG, but its emission bandwidth at cryogenic temperature remains much broader, which is advantageous for ultrashort pulse generation and amplification. Using this laser material, a stable train of pulses at a wavelength of 1026 nm was obtained, with measured pulse duration of 2.4 ps, which is more than four times shorter than that achieved with a cryogenically-cooled Yb:YAG.

We present an efficient zero-phonon-line pumped cryogenic Yb:YAG laser passively Q-switched by Cr:YAG with different initial transmissions. At 140K, with 85% initial transmission of Cr:YAG, a maximum average output power of 5.19 W with a repetition rate of 24.7 kHz was achieved leading to a slope efficiency of 55.7%. The maximum pulse energy, minimum pulse width and peak output power obtained in this case were 0.21 mJ, 142 ns and 1.48 kW respectively.

Pulsed laser deposition (PLD) is an epitaxial growth technique capable of growing planar layers of crystals with thicknesses up to several 10's of microns. Crystal layers can be grown sequentially without intermediate sample conditioning allowing complicated structures, such as laser-active double-clad designs, to be routinely fabricated. We have recently demonstrated output powers of more than 16W and slope efficiencies of 70% for diode-bar end-pumped planar waveguide oscillators based on PLD Yb:YAG grown on YAG substrates. Here, we present our initial results on varying the growth conditions to tailor the stoichiometry, refractive index, and spectroscopic properties of PLD grown layers. This fine level of control, made possible by this technique, opens the way to bespoke and unique gain media for novel amplifier and lasers designs.

Thermal parameters of optical materials, such as thermal conductivity, thermal expansion, temperature coefficient of refractive index play a decisive role for the thermal design inside laser cavities. Therefore, numerical value of them with temperature dependence is quite important in order to develop the high intense laser oscillator in which optical materials generate excessive heat across mode volumes both of lasing output and optical pumping. We already proposed a novel model of thermal conductivity in various optical materials. Thermal conductivity is a product of isovolumic specific heat and thermal diffusivity, and independent modeling of these two figures should be required from the viewpoint of a clarification of physical meaning. Our numerical model for thermal conductivity requires one material parameter for specific heat and two parameters for thermal diffusivity in the calculation of each optical material. In this work we report thermal conductivities of various optical materials as Y₃Al₅O₁₂ (YAG), YVO₄ (YVO), GdVO₄ (GVO), stoichiometric and congruent LiTaO₃, synthetic quartz, YAG ceramics and Y₂O₃ ceramics. The dependence on Nd³⁺-doping in laser gain media in YAG, YVO and GVO is also studied. This dependence can be described by only additional three parameters. Temperature dependence of thermal expansion and temperature coefficient of refractive index for YAG, YVO, and GVO: these are also included in this work for convenience. We think our numerical model is quite useful for not only thermal analysis in laser cavities or optical waveguides but also the evaluation of physical properties in various transparent materials.

In the paper we proposed improved technique of three-dimensional waveguides writing with direct femtosecond laser inscription technology. The technique allows, for the first time of our knowledge, production of waveguides with mode field diameter larger than 200 μm. This result broadens field of application of femtosecond writing technology into bulk laser schemes and creates an opportunity to develop novel amplifiers with increased efficiency. We proposed a novel architecture of laser amplifier that combines free-space propagation of signal beam with low divergence and propagation of pump irradiation inside femtosecond written waveguide with large mode field diameter due to total internal reflection effect. Such scheme provides constant tight confinement of pump irradiation over the full length of active laser element (3-10 cm). The novel amplifier architecture was investigated numerically and experimentally in Nd:phosphate glass. Waveguides with 200 μm mode field diameter were written with high frequency femtosecond oscillator. Proposed technique of three-dimensional waveguides writing based on decreasing and compensation of spherical aberration effect due to writing in heat cumulative regime and dynamic pulse energy adjustment at different depths of writing. It was shown, that written waveguides could increase optical efficiency of amplifier up to 4 times compared with corresponding usual free-space schemes. Novelty of the results consists in technique of femtosecond writing of waveguides with large mode field diameter. Actuality of the results consists in originally proposed architecture allows to improve up to 4 times optical efficiency of conventional bulk laser schemes and especially ultrafast pulse laser amplifiers.

The spectroscopy properties and wavelength tunability of diode pumped laser based on Tm-doped mixed gadolinium-gallium-aluminium garnet Gd₃(Ga_xAl_1-x)₅O₁₂ (Tm:GGAG) single crystal were investigated for the first time. The crystal was grown by Czochralski method in a slightly oxidative atmosphere using an iridium crucible. The tested Tm:GGAG sample was cut from the grown crystal boule perpendicularly to growth direction (c-axis). The composition of sample was determined using electron microprobe X-ray elemental analysis. For spectroscopy and laser experiments 3.5mm thick plane-parallel face-polished plate (without AR coatings) with composition Gd_2.76Tm_0.0736Ga_2.67Al_2.50O₁₂ (2.67 at.% Tm/Gd) was used. A fiber (core diameter 400 μm, NA= 0.22) coupled laser diode (emission wavelength 786 nm) was used for longitudinal Tm:GGAG pumping. The laser diode was operating in the pulsed regime (10 ms pulse length, 10 Hz repetition rate, maximum power amplitude 18 W). The 145mm long semi-hemispherical laser resonator consisted of a flat pumping mirror (HR @ 1.8- 2.10 μm, HT @ 0.78 μm) and curved (r = 150mm) output coupler with a reflectivity of » 97% @ 1.8- 2.10 µm. The maximum laser output power amplitude 1.14W was obtained at wavelength 2003nm for absorbed pump power amplitude 4.12W. The laser slope efficiency was 37% in respect to absorbed pumping power. Wavelength tuning was accomplished by using 2mm thick MgF₂ birefringent filter placed inside the laser resonator at the Brewster angle. The laser was continuously tunable over 180nm in a spectral region from 1856nm to 2036 nm.

We show both numerically and experimentally that dispersion management can be realized by manipulating the dispersion of a filter in a passively mode-locked fibre laser. A programmable filter the dispersion of which can be software configured is employed in the laser. Solitons, stretched-pulses, and dissipative solitons can be targeted reliably by controlling the filter transmission function only, while the length of fibres is fixed in the laser. This technique shows remarkable advantages in controlling operation regimes in ultrafast fibre lasers, in contrast to the traditional technique in which dispersion management is achieved by optimizing the relative length of fibres with opposite-sign dispersion. Our versatile ultrafast fibre laser will be attractive for applications requiring different pulse profiles such as in optical signal processing and optical communications.

We report on a simple passive scheme to reduce the intensity noise of high-power nonlinear fiber amplifiers by use of the spectral-breathing parabolic evolution of the pulse amplification with an optimized negative initial chirp. In this way, the influences of amplified spontaneous emission (ASE) on the amplifier intensity noise can be efficiently suppressed, owing to the lower overall pulse chirp, shorter spectral broadening distance, as well as the asymptotic attractive nature of self-similar pulse amplification. Systematic characterizations of the relative intensity noise (RIN) of a free-running nonlinear Yb-doped fiber amplifier are performed over a series of initial pulse parameters. Experiments show that the measured amplifier RIN increases respect to the decreased input pulse energy, due to the increased amount of ASE noise. For pulse amplification with a proper negative initial chirp, the increase of RIN is found to be smaller than with a positive initial chirp, confirming the ASE noise tolerance of the proposed spectral-breathing parabolic amplification scheme. At the maximum output average power of 27W (25-dB amplification gain), the incorporation of an optimum negative initial chirp (-0.84 chirp parameter) leads to a considerable amplifier root-mean-square (rms) RIN reduction of ~20.5% (integrated from 10 Hz to 10 MHz Fourier frequency). The minimum amplifier rms RIN of 0.025% (integrated from 1 kHz to 5 MHz Fourier frequency) is obtained along with the transform-limited compressed pulse duration of 55fs. To our knowledge, the demonstrated intensity noise performance is the lowest RIN level measured from highpower free-running femtosecond fiber amplifiers.

During the early 1990s, collaboration between the German Aerospace Center and the University of Stuttgart started to work on the Thin Disk concept. The core idea behind the thin disk design is the use of a thin, disk-shaped active medium that is cooled through one of the flat faces of the disk. This ensures a large surface-to-volume ratio and therefore provides very efficient thermal management. Today, the thin disk concept is used in various commercial lasers – ranging from compact, efficient low power systems to multi-kW lasers, including cw lasers and also pulsed (femtosecond to nanosecond) oscillators and amplifiers. The whole development of the Thin Disk laser was and will be accompanied by numerical modeling and optimization of the thermal and thermo-mechanic behavior of the disk and also the heat sink structure, mostly based on finite element models. For further increasing the energy and efficiency of pulsed Thin Disk lasers, the effects of amplified spontaneous emission (ASE) are a core issue. Actual efforts are oriented towards short pulse and ultra-short pulse amplifiers with (multi-)kW average power or Joule-class Thin Disk amplifiers, but also on new designs for cw thin disk MOPA designs.

The efficient generation of a cylindrically (radially or azimuthally) polarized LG₀₁ mode was investigated using a ring-shaped pumping distribution in a high-power Yb:YAG thin-disk laser setup. This was realized by implementing a 300 mm long customized fused silica fiber capillary in the pump beam path of the pumping optics of a thin-disk laser. Furthermore, a grating waveguide mirror based on the leaky-mode coupling mechanism was used as one of the cavity end mirrors to allow sufficient reduction of the reflectivity of the polarization state to be suppressed in the resonator. In order to achieve efficient laser operation, an optimized mode overlap between the ring-shaped pump spot and the excited first order Laguerre-Gaussian doughnut mode is required. This was investigated theoretically by analyzing the intensity distribution generated by different fiber geometries using a commercially raytracing software (Zemax). The output power, polarization state and efficiency of the emitted laser beam were compared to that obtained with a standard flattop pumping distribution. In particular, the thermal behavior of the disk was investigated since the excessive fluorescence caused by the non-saturated excitation in the center of the homogeneously pumped disk leads to a strong heating of the crystal. This considerable heating source is avoided in the case of the ring-shaped pumping and a reduction of the temperature increase on the disk surface of about 21% (at 280 W of pump power) was observed. This should allow higher pump power densities without increasing the risk of damaging the disk or distorting the polarization purity. With a laser efficiency of 41.2% to be as high as in the case of the flattop pumping, a maximum output power of 107 W was measured.

We present our latest achievements on the amplification of ultrafast beams with radial polarization using a thin-disk multipass amplifier. Starting with a seed laser (TruMikro5050 provided by the company TRUMPF laser GmbH) delivering a linearly polarized beam with 115 W of average output power, 6.5 ps pulse duration at a repetition rate of 300 kHz, we could extract radially polarized laser pulses with an average output power of 635 W and a pulse energy of 2.1 mJ. The radial polarization was obtained by using a segmented wave-plate placed in front of the amplifier. This is, to the best of our knowledge, the highest average output power and pulse energy reported so far for radially polarized ultrafast lasers. A scheme for direct amplification of such ring-shaped radially polarized laser beams is presented together with a possible solution to compensate for the depolarizing phase shift introduced by the optical components in the amplifier.

We present a SESAM-modelocked Yb:CaF₂ thin-disk laser designed for pulse durations below 300 fs and high peak powers of more than 5 MW. A cavity for fundamental mode operation (beam quality factor M² below 1.2) was set up and modelocked using a SESAM. An average output power of up to 17.8 W was obtained at a repetition-rate of 10 MHz, corresponding to a pulse energy of approximately 1.8 μJ. The pulse duration was measured to be 285 fs, therefore a peak power of 5.5 MW was attained. Our research enables a comparison of the potential of Yb:CaF2 with other Yb-doped crystals with broad gain bandwidth in thin-disk laser technology. We conclude from our results that this gain material is very promising for high pulse energies and high peak powers.

The spectral characteristics of laser active media, and thus those of the laser output, are temperature dependent. Specifically, in almost every crystal host, cooling to low temperatures leads to better heat removal, a higher efficiency and output power, and a reduced lasing threshold. Tm-ion doped lasers have an emission wavelength around 2 μm and are important in medicine for soft tissue cutting and hemostasis, as well as in LIDAR or atmosphere sensing technology. This paper presents the performance-temperature dependency of a 4 at. % doped Tm:YAP microchip. During the experiment the Tm:YAP crystal was placed inside an evacuated liquid nitrogen cryostat on a cooling finger. As its temperature was varied from 80 K to 340 K, changes were observed in the absorption spectrum, ranging from 750 nm to 2000 nm and in the fluorescence spectrum from 1600 nm to 2050 nm. Fluorescence lifetime was seen to rise and fall with decreasing temperature. The laser was pumped by a 792 nm laser diode and at 80 K the maximum output peak power of the laser was 4.6 W with 23 % slope efficiency and 0.6 W threshold, compared to 2.4 W output peak power, 13 % slope efficiency and 3.3 W threshold when at 340 K. The laser emission wavelength changed from 1883 nm to 1993 nm for 80 K and 300 K, respectively.

In this communication, we demonstrate a passive mode-locked Er:Yb co-doped double-clad fiber laser using a tapered microfiber topological insulator (Bi₂Se₃) saturable absorber (TISA). The topological insulator is drop-casted onto the tapered fiber and optically deposited by optical tweezer effect. We use a ring laser setup including the fabricated TISA. By carefully optimizing the cavity losses and output coupling ratio, the mode-locked laser can operate in L-band with a high average output power. At a maximum pump power of 5 W, we obtain the 91^st harmonic mode-locking of soliton bunches with a 3dB spectral bandwidth of 1.06nm, a repetition rate of 640.9 MHz and an average output power of 308mW. As far as we know, this is the highest output power yet reported of a mode-locked fiber laser operating with a TISA.

In this paper we demonstrate a preliminary work done on employing antimony telluride (Sb₂Te₃) topological insulator as a saturable absorber for Yb-doped fiber lasers. The material was deposited onto a side-polished fiber by means of a pulsed magnetron sputtering technique. Fabricated absorber was implemented in an all-normal dispersion cavity and allowed for self-starting dissipative soliton generation. The laser emitted stable pulse train at a repetition rate of 17.07 MHz with 4.25 nm broad output spectrum centered around 1039.4 nm. Average output power amounted to 0.54 mW with 32 pJ pulse energy.

A graphene passively Q-switched single frequency Ho:YAG laser was demonstrated. Ho:YAG crystal was resonantly pumped by a 1908 nm diode laser. Twisted-mode single frequency technique was applied to realize single frequency oscillation. The maximum single frequency laser output was 358 mW. Single frequency pulse laser output was achieved by inserting a graphene into the single frequency Ho:YAG laser. The maximum average power of 149 mW was obtained with the pulse repetition rate of 40.45 kHz under 8.32 W of incident pump power.

We propose a novel mode-locked fiber laser design which features a passive nonlinear triangular pulse formation and self-similar parabolic pulse amplification intra cavity. Attribute to the nonlinear reshaping progress in the passive fiber, a triangular-profiled pulse with negative-chirp is generated and paved the way for rapid and efficient self-similar parabolic evolution in a following short-length high-gain fiber. In the meanwhile, the accompanied significantly compressed narrow spectrum from this passive nonlinear reshaping also gives the promise of pulse stabilization and gain-shaping robustness without strong filtering. The resulting short average intra-cavity pulse duration, low amplified spontaneous emission (ASE) and low intra-cavity power loss are essential for the low-noise operation. Simulations predict this modelocked fiber laser allows for high-energy ultra-short transform-limited pulse generation exceeding the gain bandwidth. The output pulse has a de-chirped duration (full-width at half maximum, FWHM) of 27 fs. In addition to the ultrafast laser applications, the proposed fiber laser scheme can support low-noise parabolic and triangular pulse trains at the same time, which are also attractive in optical pulse shaping, all-optical signal processing and high-speed communication applications.

Three numerical methods for the design of Kerr Lens Mode-Locking (KLML) ultrashort pulse cavities that use a solid state Brewster-cut nonlinear gain medium are compared. The nonlinear medium is modeled first deploying a matrix approximation that considers non-coupled (tangential analysis is independent of sagittal analysis) Kerr and thermal self-focusing; and second with a differential equation that relates the real and imaginary parts of the inverse of the complex Gaussian beam parameter. The third comparison is against a matrix analysis method that considers the coupling between the sagittal and tangential modes inside the nonlinear medium in order to determine the impact of this effect. The three methods search the self-consistency condition for the complex beam parameter and the results are compared.

A high-repetition-rate, high-peak-power burst-mode laser for laser-based measurement applications is presented by using a master oscillator power amplifier structure. An laser diode arrays (LDA) side-pumped Nd:YAG acousto-optical (A-O) Q-switched laser serves as the master oscillator. Under pulsed pumping, pulse trains with 2-25 pulses are obtained when the repetition rate changes from 10 kHz to 100 kHz. The maximum pulse burst energy of 31.2 mJ is achieved in the A-O Q-switched pulse burst laser oscillator at 10 kHz. Two LDA side pumped Nd:YAG modules are employed in the amplification stage. After the amplification, the pulse burst energy at 10 kHz reaches ~170 mJ with a single pulse energy of 85.2 mJ and a pulse width of 14.5 ns, generating a peak power of 6.1 MW. At 100 kHz, the total burst energy reaches 220 mJ with a single pulse energy of 8.8 mJ in the pulse burst laser system.

We report on theoretical investigation of quasi-three level Er:YAG laser. We propose a numerical model of the laser design with side pump by 1471 nm laser diodes. The model describes the dynamical propagation of the pump in the cavity and the kinetic parameters of the active medium.

We present an experimental demonstration of a class of beams, namely Frozen Waves, that can carry predetermined longitudinal intensity profiles in the presence of modeled loss. These waveforms consist of a superposition of equal frequency Bessel beams with different transverse and longitudinal wavenumbers, and are generated using a programmable spatial light modulator addressed by computer-generated hologram. Attenuation-resistant Frozen Waves can address challenges associated with light-matter interaction in absorbing media encountered in imaging, remote sensing, and particle micro-manipulation, to name a few.

Femtosecond laser micro machining of surfaces knows a gain of interest as it demonstrates efficient and precise processing with reduced side effects around the irradiated zone, and also because of the remarkable costs reduction and reliability improvements of nowadays commercially available sources. Controlling the intensity distribution spatially can offer a supplementary degree of flexibility and precision in achieving user-defined ablation spatial profile, drilling, cutting of materials or in-volume laser-induced modifications. In this scope, the possibility to generate a top-hat intensity distribution by spatially shaping the beam wavefront is studied in this work. An optimization of Zernike polynomials coefficients is conducted to numerically determine an adequate phase mask that shapes the laser intensity distribution following a targeted top hat distribution in the processing plane, usually at the focal length of a converging lens. The efficiency of the method is numerically investigated in the optimization by evaluation of the root mean square error (RMS) between the top-hat target and the calculated laser distribution in the far field. We numerically verify that acceptable top-hat beam shaping of various size can be achieved with a sufficient number of Zernike polynomials, opening the way to phase mask calculations adapted to the wavefront modulator ability to reproduce Zernike polynomials.

Random lasers are laser sources in which the feedback is provided by scattering instead of reflection and which, for this reason, do not require surfaces with optical finish such as mirrors. The investigation of such lasing action in a large variety of disordered materials is a subject of high interest with very important applications such as threedimensional and speckle-free imaging, detection of cancer tissue and photonic coding and encryption. However, potential applications require optimization of random laser performance especially with respect to optical efficiency and directionality or brightness. This work demonstrates such an optimization procedure with the goal of achieving a random laser with sufficient efficiency and brightness in order to be used in practical applications. Two random lasers are demonstrated, one solid and on liquid, that fulfil directionality and efficiency requirements. The first one consists of a neodymium doped powder laser with a record slope efficiency of 1.6%. The second one is a liquid random laser injected into a HC-ARROW waveguide which uses a microchannel connected to a much larger reservoir in order to achieve the necessary directionality. Both devices can be produced by low cost fabricating technologies and easily integrated into next-generation, lab-on-chip devices used for in-situ determination of infectious tropical diseases, which is the main goal of this project.

Optical filters with relatively large FSR and narrow linewidth are simultaneously needed for different applications. The ratio between the FSR and the 3-dB linewidth is given by finesse of the filter, which is solely determined by the different energy loss mechanisms limited by the technology advancement. In this work, we present a novel coupled-cavity configuration embedding an optical filter and a gain medium; allowing an overall finesse enhancement and simultaneous FSR and 3-dB linewidth engineering beyond the technological limits of the filter fabrication method. The configuration consists of two resonators. An active ring resonator comprises an optical gain medium and a passive resonator. In one configuration, the optical filter is the passive resonator itself. In a second configuration, the passive resonator is another ring resonator that embeds the optical filter. The presented configurations using a semiconductor optical amplifier are applied one time to a mechanically Fabry-Perot filter in the first presented configuration; and a second time to a fiber ring filter in the second presented configuration. The mechanical filter has an original 3-dB linewidth of 1nm and an FSR that is larger than 100nm while the enhanced linewidth is about 0.3nm. The fiber ring filter length is 4 m and directional coupler ratios of 90/10corresponding to a 3-dBlinewidth of about 4MHz and an FSR of 47 MHz. The enhanced 3- dBlinewidth of the overall filter configuration is 200kHz, demonstrating finesse enhancement up to20 times the original finesse of the filter.

Laser Induced Breakdown Spectroscopy (LIBS) is a multi-elemental analysis technique with various advantages and has the ability to detect any element in real time. This technique holds a potential for environmental monitoring and various such analysis has been done in soil, glass, paint, water, plastic etc confirms the robustness of this technique for such applications. Compared to the currently available water quality monitoring methods and techniques, LIBS has several advantages, viz. no need for sample preparation, fast and easy operation, and chemical free during the process. In LIBS, powerful pulsed laser generates plasma which is then analyzed to get quantitative and qualitative details of the elements present in the sample. Another main advantage of LIBS technique is that it can perform in standoff mode for real time analysis. Water samples from industries and agricultural strata tend to have a lot of pollutants making it harmful for consumption. The emphasis of this project is to determine such harmful pollutants present in trace amounts in industrial and agricultural wastewater. When high intensity laser is made incident on the sample, a plasma is generated which gives a multielemental emission spectra. LIBS analysis has shown outstanding success for solids samples. For liquid samples, the analysis is challenging as the liquid sample has the chances of splashing due to the high energy of laser and thus making it difficult to generate plasma. This project also deals with determining the most efficient method for testing of water sample for qualitative as well as quantitative analysis using LIBS.