This PDF file contains the front matter associated with SPIE Proceedings Volume 11266 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

The bio-laser is an emerging technology in biosensing and imaging. In contrast to traditional fluorescence based measurement, lasing emission is used as the sensing signal, which has strong intensity, threshold behavior, and narrow linewidth, and is free of background. In this presentation, we will first discuss the principle of bio-lasers. Then we will describe the development of the laser emission microscope based on bio-lasers for tissue imaging that can be used for cancer diagnosis.

A rather unknown method to perform optical frequency tuning is the adiabatic frequency conversion. But this method has some appealing advantages compared to conventional frequency conversion schemes, i. e. nonlinear- optical based ones: The internal conversion efficiency can reach unity even on a single-photon level. No threshold and no phase-matching conditions need to be fulfilled. Previous realizations of adiabatic frequency conversion suffer from short photon lifetimes, limited tuning range and challenging experimental setups. Here, we employ the Pockels effect for adiabatic frequency conversion (AFC) in a non-centrosymmetric ultrahigh-Q microresonator made out of lithium niobate. With a 70-μm-thick resonator we observe frequency shifts of more than 5 GHz by applying a moderate voltage of 20V. In contrast to former schemes our setup is considerably simplified and provides a linear electric-to-optical link that enables us to generate also arbitrary waveforms of frequency shifts. Furthermore, our presented conversion scheme is well-suited for on-chip fabrication. Volume fabrication and application of larger electric fields for reasonable voltages become possible. By doing this, it is feasible to achieve tuning on the order of hundreds of GHz.

Recently, low-loss (0.027 dB/cm) ridge waveguides have been demonstrated on lithium niobate on insulator (LNOI) by laser patterning followed by chemo-mechanical polishing. However, the fabricated waveguide supports multi-mode propagation due to the relatively large cross-sectional dimensions. Here, we report conversion of the multi-mode LNOI waveguides into single mode waveguides with a mode field size of ~2.5 μm with a cladding layer of Ta₂O₅. The propagation loss of the single mode waveguide is measured to be ~0.042 dB/cm. Most importantly, we show that this fabrication approach has allowed to fabricate meter-length long LNOI single mode waveguides of low propagation loss.

Whispering gallery resonators made out of crystalline materials exhibiting second-order nonlinearities enable frequency mixing such as optical parametric oscillation with high efficiency at low optical input powers and are ideally suited to realize versatile and compact optical frequency converters. Recent achievements stimulate this field further: Frequency conversion not only at a single wavelength or with few wavelengths is possible, entire frequency combs can be transferred into different spectral domains, e.g., allowing the realization of frequency combs in spectral regions that are suitable for multicomponent analytics like the mid-infrared region. Furthermore, these resonators are also supposed to be the ideal host for cascaded nonlinearities allowing the build-up of frequency combs based on second-order nonlinearities. All this comes with new and better schemes to tune whispering gallery resonators, providing advanced opportunities to modulate the laser wavelengths with nanosecond speed employing the Pockels effect. Juggling with light: We will summarize in the presentation these recent achievements, demonstrating that in the field of whispering gallery resonators still many discoveries are ahead of us.

We report fabrication and characterization of ultra-low loss optical waveguides and optical micro-resonators on lithium niobate on insulator with excellent surface qualities. We demonstrate innovative and high-performance applications and/or devices ranging from nonlinear optics and electrically tunable optomechanics to microcombs and integrated circuits.

"Soliton microcombs for LIDAR" was recorded at Photonics West 2020 in San Francisco, California.

“Optical microresonators in clocks: Needs and status” was recorded at Photonics West 2020 held in San Francisco, California, United States.

On-chip Kerr frequency combs have attracted significant attention because of their compact footprint and numerous applications. While many integrated material systems are being investigated for generating the on-chip Kerr frequency combs, so far only silica devices have achieved quality factors above 100 million, which is important for decreasing the threshold and power consumption of the system. However, as an intrinsic property of silica, the hydroxyl groups present on the surface of the devices will attract water molecules in the air, which decreases the quality factor of the devices. To maintain the performance of the frequency combs, methods like putting the devices in nitrogen purged boxes or building covers for the system are proposed, which would largely increase the complexity of the system. Here we studied another material system, silicon oxynitride microtoroids, whose quality factors can achieve and stay constant at more than 100 million because of the lack of the hydroxyl groups on the surface. Kerr frequency combs are generated from the SiOxNy microtoroids with normal dispersion with avoided mode crossing. Thresholds as low as 280 μW are achieved as a result of the high quality factor. The comb spectrum remains the same for the same pump power over the nine day period after fabrication, which indicates that the performance of the frequency combs remains constant despite the silicon oxynitride devices being stored in ambient atmosphere without any special treatment the whole time.

Optical frequency combs are a key technology for precision measurements. In the past years, microresonatorbased frequency combs based on third-order χ ⁽³⁾ (Kerr) nonlinearities have attracted significant attention thanks to their small footprint and their wide-ranging applications in fields such as telecommunications, molecular spectroscopy or ultrafast distance measurements. In this contribution, we present a frequency comb generated in a microresonator made of 5% MgO-doped congruent lithium niobate, a non-centrosymmetric crystalline material, employing the generally much stronger second-order χ ⁽²⁾-nonlinearities of such a material via a scheme of cascaded nonlinear processes. This approach paves the way towards reduced pump thresholds for comb generation and comes with intrinsic suitability for self-referencing.

We demonstrate continuous scanning of a dissipative Kerr micro-resonator soliton comb (hereafter called soliton comb). Detuning between a cw pump laser and a resonance of a microresonator is fixed via Pound-Drever-Hall (PDH) locking during scanning so as to maintain soliton operation. We show continuous comb mode scanning of as large as 190 GHz by heating the microresonator. In addition, with the frequency-scanned soliton comb, we demonstrate broadband, high resolution spectroscopy, showing spectral features with a bandwidth of as small as 5 MHz, while covering more than 2 THz spectrum.

We have developed an experimental setup in order to study whispering gallery mode resonators in the pulsedpump regime. Since the pulse repetition rate needs to match the free spectral range of the resonator, the pulse generator we have built is flexible in terms of both pulse repetition rate and pulsewidth. A rich variety of dynamical phenomena are observed in the system.

Optical resonant cavities form the foundation for a wide range of integrated optical components. While a high performance laser requires a high quality factor (Q) cavity, other types of devices, like modulators, rely on the cavity resonant wavelength being tunable. Numerous mechanisms based on the thermo-optic and electro-optic effects have been leveraged to create switchable or tunable devices; however, these are very power hungry and/or require complex control machinery. In the present work, we graft an air-stable, optically triggerable functional group to the surface of an ultra-high-Q optical cavity. The Aazobenzene functional group switches from trans to cis upon exposure to blue light, and it can be thermally triggered to revert to the initial trans state. Using a single tapered optical fiber waveguide, blue and near-IR light can be coupled into the device simultaneously. When the blue light interacts with the Aazo group, the resonant wavelength blue shifts. Upon exposure to a CO2 laser, the resonant wavelength returns to its initial position. Several different aspects of the device operation were investigated, including the kinetics of the switching, the effect of switching via a resonant or non-resonant optical field, and sterics of the switching. Notably, by tuning the surface density of the Aazo groups using a multi-material surface chemistry, it is possible to control the magnitude of the shift.

We propose and experimentally demonstrate an alternative WGR coupling scheme that is easy to make, requires little alignment, and is both convenient and stable with no need for phase matching. It relies on cavity enhanced Rayleigh scattering. This is the first, single-ended, fiber-based optical nano-antenna that can be used to simultaneously excite and collect light from the WGMs of a microresonator, coupling efficiency as high as 13% is observed, making it very promising for optical sensing applications or cQED.

The use of beams carrying orbital angular momentum (OAM) has become ubiquitous and topical in a variety of research fields. More recently, there has been a growing interest in exotic OAM carrying beams with spatially variant polarisation, so called Poincaré sphere beams. Structuring these beams at the source gives rise to compact solutions for a myriad of applications, from laser materials processing to microscopy. Here we present a visible laser that control's the angular momentum of light by arbitrary spin-orbit (SO) momentum conversion using novel metasurface devices. Further, we outline how to generate high purity OAM states in a deterministic manner with charge up to 100. Finally, we demonstrate the generation of symmetric and non-symmetric vector vortex beams from the same source with a large OAM differential between modes of up to 90. The performance and versatility in design of our approach offers a route to control light's angular momentum at the source.

Photoswitchable organic molecules can undergo reversible structural changes with an external light stimulus. These optically controlled molecules have been used in the development of “smart” polymers, optical writing of grating films, and even controllable in-vivo drug release. Being the simplest class of photoswitches in terms of structure, azobenzenes have become the most ubiquitous, well-characterized, and implemented organic molecular switch. Given their predictable response, they are ideally suited to create an all-optically controlled switch. However, fabricating a monolithic optical device comprised solely from azobenzene while maintaining the photoswitching functionality is challenging. In this work, we combine integrated photonics with optically switchable organic molecules to create an optically controlled integrated device. A silica toroidal resonant cavity is functionalized with a monolayer of an azobenzene derivative. After functionalization, the loaded cavity Q is above 10⁵ . When 450 nm light is coupled into cavity resonance, the azobenzene isomerizes from trans-isomer to cis-isomer, inducing a refractive index change. Because the resonant wavelength of the cavity is governed by the index, the resonant wavelength changes in parallel. At the probe wavelength of 1300 nm, the wavelength shift is determined by the duration and intensity of the 450 nm light and the density of azobenzene functional groups on the device surface, providing multiple control mechanisms. Using this photoswitchable device, resonance frequency tuning as far as sixty percent of the cavity’s free spectral range in the near-IR is demonstrated. The kinetics of the tuning agree with spectroscopic and ellipsometry measurements coupled with finite element method calculations.

We report here the observations of high Q (up to 7 x 10⁷) Whispering Gallery Modes in liquid microdrops of a glycerol-water mixture and three different silicone oils, which are excited and detected using high transmission tapered fibers of sub-micron waist sizes. For measuring the real Q values, which are not thermally limited, the laser frequency is scanned fast enough such that the broadband thermal oscillations of microdrops, with frequencies from kHz to 100s of kHz, do not affect the resonance signal. The two standard measurement methods `linewidth measurement' and `cavity ring-down' are used - the first one for resonances with Q <10⁷ and the second one for Q ^>_~ 10⁷. We describe our analysis to show that for the tested liquids, absorption loss plays the dominant role in deciding the maximum value of the measured intrinsic Q of the microdrops. Using the analysis we show that the measured optical Q can be used to estimate a reliable upper limit of the absorption coefficient of liquids.

Narrow-linewidth lasers operating in the near-infrared provide precise timing synchronization for atomic optical clocks and quantum computers. Crystalline ultra-high-Q optical resonators enable high-performance laser design in a small form factor that allow miniaturization of the devices using the lasers. Here we demonstrate a 780 nm self-injection-locked laser with Hertz-level instantaneous linewidth under single-mode continuous-wave operation. The self-injection locking induced by the whispering gallery mode resonator suppresses the frequency noise and reduces the drift of the free running device.

We present a new device platform which defines on-chip chalcogenide waveguide/resonators without directly etching chalcogenide. Using our platform, we have demonstrated chalcogenide ring resonators with record high Q-factor exceeding 1.1x10⁷ which is 10 times larger than previous record on on-chip chalcogenide resonators. A ring cavity is designed and fabricated for Stimulated Brillouin lasing on our platform. Thanks to the high-Q factor, Brillouin lasing with threshold power of 1 mW is demonstrated. This value is more than an order of magnitude improvement than previous world record for on-chip chalcogenide Brillouin lasers. We also developed an efficient and flexible method for resonator waveguide coupling with our device platform. Coupling between a resonator and a waveguide can be varied from under coupled region to over-coupled region.

Whispering gallery resonators (WGRs) are ideally suited for the realization of miniaturized lasers. Due to their high quality factor and small mode volume, they allow for low-threshold and narrow-linewidth emission from (sub)millimeter-sized cavities made of laser-active materials. However, so far the majority of experimental realizations relies on expensive pump light sources like narrow-linewidth or pulsed laser systems, impeding most applications. We demonstrate two whispering-gallery-based single-frequency lasers pumped by compact spectrally multimode low-cost laser diodes. The spheroidally-shaped millemeter-sized WGRs are made of Pr:LiLuF₄ and Nd:YVO₄. They provide quality factors beyond 10⁷ at the lasing wavelengths (640 nm and 1064 nm, respectively). The pump light is focused onto the rim of the WGR. We observe single frequency emission at milliwatt output powers. The temporal stability of the output power and of the output frequency are determined to be ±1:5 % and ±30 MHz within 30 min, respectively. By changing the temperature of the cavity, we achieve mode-hop-free tuning exceeding 11 GHz.

Dielectric whispering-gallery-mode resonators are a great tool to entrap electro-magnetic radiation throughout the dielectric’s transparency range[1]. I will discuss hybrid systems which are resonant for both microwave and optical fields and that allow for second order nonlinear effects. In an efficient resonant system and for strong microwave and optical fields, sum- and difference frequency generation can cascade, leading to optical frequency combs[2]. For the limit of very weak microwaves and only sum frequency generation, coherent conversion of microwave signals allows the quantum state of individual microwave photons to be transferred into the optical domain[3], useful for connecting future superconducting-qubits-based quantum-networks. 1. D.V. Strekalov, C. Marquardt, A.B. Matsko, H.G.L. Schwefel, and G. Leuchs, Journal of Optics 18, 123002 (2016). 2. A. Rueda, ... and H.G.L. Schwefel, Nature 568, 378 (2019). 3. A. Rueda, ... and H.G.L. Schwefel, Optica 3, 597 (2016)

Optical Gaussian entangled states can be generated deterministically, up to very large number of modes. Furthermore, for nontrivial quantum computation, non-Gaussianity is required, which can be obtained from photon subtraction. We will explore here the controlled generation of multimode graph states from ultrafast optical pulses (optical frequency combs) and parametric down conversion in a synchronously pumped cavity, investigating in particular spectral shaping of the pump. Mode dependent photon subtraction is then implemented through sum-frequency generation, and characterization is performed through frequency resolved homodyne detection. We study the influence of a non Gaussian ingredient on a Gaussian graph state.

A key challenge in today’s quantum science is the realization of large-scale complex non-classical systems to enable e.g. ultra-secure communications, quantum-enhanced measurements, and computations faster than classical approaches. Optical frequency combs represent a powerful approach towards this, since they provide a very high number of temporal and frequency modes which can result in large-scale quantum systems. Here, we discuss the recent progress on the realization of integrated quantum frequency combs and reveal how their use in combination with on-chip and fiber-optic telecommunications components can enable quantum state control with new functionalities, yielding unprecedented capability.

The practical implementation of quantum computing faces the two key requirements of achieving scalability and maintaining quantum coherence. While the latter has been reached by ion-trap and superconducting qubit platforms to the level required for quantum error correction to take place, the former has been reached to record levels (thousands of qubit equivalents, called qumodes) using the quantum optics of entangled electromagnetic fields. In this talk, I will present the experimental realization of quantum computing substrates called cluster entangled states in the optical frequency comb of a single parametric oscillator, and prospects for translation in integrated optics.

We develop schemes to generate, manipulate and detect single photons at various frequencies including telecom wavelengths. With detectors based on superconducting nanowires we combine very high detection efficiency with high time resolution and very low noise levels. We demonstrate on-chip implementation of single photon techniques as well as long distance implementations using deployed optical fibers.

This Conference Presentation, “What is the maximum accessible OAM from spatial light modulators?” was recorded at Photonics West LASE 2020, held in San Francisco, California, USA.

Ultrafast femtosecond and high power CW laser systems are extensively used in the fields of science and technology. However, due to the wide emission spectra in ultrashort pulse and high power CW lasers, it is quite difficult to manipulate their transverse mode structure with conventional monochromatic phase masks. Here we present transverse mode conversion from the fundamental order TEM00 broadband lasers beams to different TEM and Laguerre-Gauss orders with the use of a broadband phase mask based on Volume Bragg Grating recorded in Photo-Thermo-Refractive (PTR) glass. The overall diffraction efficiency of the achromatic phase mask was 94%.

We present a high-power capable, simple, tunable, and robust vortex beam generator. Initial phase profiles are generated using a Spatial Light Modulator and then holographically encoded into a Transmitting Volume Bragg Grating (TBG) resulting in fabrication of a Holographic Phase Mask (HPM). Such HPMs could be used for mode conversion (e.g. Gaussian to vortex) at high power due to low absorption and low nonlinear refractive index of photo-thermo-refractive glass. Unlike monochromatic conventional phase mask, adjustment of an incidence angle on the HPM results in conservation of the phase information incurred into the beam making HPM tunable.

Zeroth order Bessel beams are widely used in laser micromachining of transparent materials. The small diameter of central core and elongated focus enables to generate high aspect ratio voids. The simplest way to generate this beam is to induce a conical shape phase with an axicon. However, the quality of the axicon tip is very crucial to generate smooth Bessel beams since it is known that a blunt axicon tip induces large intensity modulation in propagation direction. Alternative Bessel beam generation method is to use a Diffractive Optical Elements (DOEs) that do not suffer from previously mentioned problem. In this work we demonstrate generation of a zeroth order Bessel beam with Geometric Phase Optical Elements (GPOEs) (manufactured by Workshop of Photonics) acting as a diffractive beam shaping element. Having absolute control of induced beam phase, we have modified mask phase so that half of it had additional phase shift or spatial transposition resulting in creation of fanciful induced beam phase patterns. With the use of laser beam propagation numerical modeling we show that these new phase masks can create various beam transverse intensity patterns such as asymmetrical central core, generation of multiple peaks or even large rings that are highly demanded for various laser micromachining applications. We have chosen couple of most perspective beam shapes and manufactured GPOEs to generate them. The experimentally generated beams were compared to numerical simulations. As the GPOEs are able to work with high power pulses we have also investigated induced transparent material modifications.

Multi-Plane Light Conversion (MPLC) is an innovative shaping technique which allows theoretically lossless complex beam shapes. The free-space reflective design is particularly well suited to Ultra-Short Pulse (USP) laser-based processes challenges. We demonstrate the system high stability over long processing times thanks to a mode cleaning feature. Here we show micro-cutting and engraving tests carried out on stainless-steel and brass with a high power, industrial, USP laser having squared, and circular top-hat profile generated using MPLC technology. Thanks to the sharp edges of the profile, a sensible reduction of the taper and optimization of the overlapping is observed

A novel optical concept is introduced with standard components for highly efficient coherent beam combining a system of (N x N) beams. In a proof-of-principle experiment a well-defined setup with microlens arrays (MLAs) is used to create a beam matrix of 5 x 5 beams. For the combination step the same setup is employed, and the created 25 beams are combined. A combination efficiency above 90% is achieved. Furthermore, the concept allows for dynamic beam combination, i.e., the resulting number of beams and corresponding positions can be controlled by the absolute phases of the array of input beams. A proof-of-principle experiment shows excellent agreement with the model.

Extreme-ultraviolet (EUV) lithography employs a high-power short-pulse carbon dioxide (CO₂) laser based on master oscillator power amplifier architecture to produce Sn plasma generating the EUV light. We demonstrate multiline oscillation of a CO₂ laser with 20 ns of pulse duration for the master oscillator. An intracavity diffraction grating enables the 5-line oscillation (10.55, 10.57, 10.59, 10.61, and 10.63 μm) by separating the different 5 lines spatially in a gasdischarge gain medium. The multiline CO₂ laser employs a cavity length of 3000 mm and an electro-optically Q-switched cavity dumping to generate 20-ns laser pulses. The maximum output power is 10.6 W at 100-kHz repetition rate and the output stability is ±1.2% at 3σ over 30 minutes. The grating combines the separated 5 optical axes into one optical axis inside the cavity, which realizes the nearly single-mode (TEM00) oscillation with ~1.1 of M².

Low heat generation can be obtained when pumping Nd:YLF at wavelengths of 872 nm and 880 nm and emitting at the three-level transition of 908 nm. These transitions show very low quantum defect with efficiencies of 0.96 and 0.97, respectively. However, the low average absorption cross-section at these wavelengths makes efficient absorption even for longitudinal pump setups difficult. Using a beam-shaped pump diode instead of a fiber-coupled diode bar may be an effective means of increasing absorption because it can provide for π-polarized radiation which shows higher absorption cross section. In this work, a Nd:YLF was pumped at 872 nm by a diode bar using beam-shaping. Results were compared to pumping at 872 and 880 nm with non-polarized fiber-coupled diodes. Stimulated Raman scattering was also obtained with a KGW crystal generating first Stokes emissions at 990 nm and 976 nm.

Injection semiconductor lasers have achieved a considerable role in fundamental research and technological applications because of their numerous advantages with respect to other types of laser, such as high conversion efficiency, low power consumption, small size and low cost. Nevertheless, the maximum power that can be extracted from a single laser chip is relatively small. Most of the research efforts are nowadays dedicated to find novel strategies to increase the laser power at no expense of the laser brightness.

Currently, the most used solution relies on the combination of different laser beams and, depending on the application, different types of combining can be identified. In this work, we will present the numerical modeling of a novel laser resonator design that makes possible the interferometric combination of beams coming from different gain chips in an intra-cavity configuration to increase the overall laser power with no compromise on the laser brightness.

We present an overview of pump-induced lensing effects in end-pumped Alexandrite lasers. The dioptric lens power is measured for a diode pumped Alexandrite laser using a Shack-Hartmann wavefront sensor under both non-lasing and lasing conditions. Under non-lasing conditions, the lens dioptric power is measured for two pump sizes and in both cases is found to be nearly linear with respect to the absorbed pump power. Under lasing conditions the lens dioptric power is up to 60% weaker. Good agreement is found between the non lasing and lasing experimental results using a model based on a combined lens consisting of a thermal lens, and a population lens arising from the electronic component of the refractive index. Fitting parameters using an analytical model for the two pump sizes are also found to be consistent. Values for the difference in excited to ground state polarizability are obtained and found to be consistent with prior measurements for Alexandrite and other Chromium-doped gain media.

Diode-side pump Nd:YAG rod modules are widely available, reliable and commercially very attractive for building continuous-wave solid-state lasers in the 10-1000 W range. Newer technologies such as fiber or thin disk lasers are generally much more expensive but have the benefit of better beam quality and higher output powers if necessary. By using well-known techniques for designing dynamically stable resonators (DSRs), lasers with high extraction efficiency and high beam quality (fundamental mode, TEM₀₀) can be obtained also with diode side-pumped modules. However, a successful project for a dynamic stable laser depends critically on the correct choice of the fundamental mode diameter within the rod. DSR design rules are based on the beam waist, w₃, at the rod principal planes by considering the rod as a thin thermal lens, which differs significantly from real resonators. Here we give guidelines and criteria on how to establish the correct diameter in each case. Using off-the-shelf 75 W Nd:YAG modules it was possible to obtain linearly polarized TEM₀₀-mode output of 30 W with M²=1.08 from a single module, M²=1.2 and 76.5 W of output power using two modules and 100.5 W of polarized, continuous output with M²=1.8. A single-frequency ring laser was also built, using two modules, generating 51.6 W of fundamental wave single-frequency output.

A multi-kilowatt high-power fibre laser with adjustable azimuthal mode output beam profile is presented for the first time. The beam properties, and applications in laser cutting and welding of various metals are presented.

As well known, the quality of radiation of laser beam is reduced during propagation along optical trace, because of various reasons (for example, atmospheric turbulence, scattering, thermal fluctuations etc.). We propose small-size deformable mirrors with high spatial resolution of control elements, that will allow to compensate for wavefront aberrations in wide range. Developed wavefront corrector could be used in different scientific areas: free-space communications, destruction of space debris, etc.

M-squared laser measurement has long been a challenging measurement; even for the expert. The problem has basically been one of too many “moving” parts in the measurement system and this coupled with the lack of any national standard save for a method of measurement (ISO 11146-1 [2005]), the high variation of measurement repeatability has been the norm. The M-square value of a laser is as important as the basic power of the laser and the two values together provide an accurate means to establish the laser systems true potential of peak power in application use. A novel optical approach has been developed which makes the M-square measurement as simple as measuring the laser power; whereby one simply aligns the M-square system to the input beam like a laser power meter; enter in a few basic parameters: wavelength, lens focal length, back focal length, etalon value and the measurement is automatic and instant. The entire laser beam caustic is measured on a single camera with extremely good signal to noise ratio from the first to beyond the third Rayleigh range within the frame rate of the sensor which provides an M-square in a fraction of a second or within a single laser pulse. Whether the user is an expert or a complete novice, the M-square value is the same from one user to another or from one measurement to another with high repeatability and stability.

The article discusses the use of stacked-actuator adaptive mirrors to improve the focusing of laser radiation. The criterion of focusing efficiency is the fraction of the energy of the laser radiation passing through the pinhole located in the focal plane of the focusing lens.

This work proposes a method that can be used to control the transverse profile of the optical intensity distribution of a diode-end-pumped solid-state laser operating with a Gaussian seed beam. The transverse gain profile in an external amplifier was temporally adjusted to control other higher-order intensity distribution. The amplifier is dual pumped by two independent diode lasers. The higher-order intensity distribution profile was created within the amplifier by independently adjusting the dual diodes output powers. This technique will permit synchronised variation of both the output power of the laser and the transverse intensity distribution of a laser beam.

This paper discusses ongoing research at Lawrence Livermore National Laboratory (LLNL) that investigates the effectiveness of a whispering gallery mode micro-resonator as a biosensor. Whispering Gallery mode resonators have properties such as ultrahigh quality factors (Q factors up to 10¹¹), very high power density, and small mode volume that make them suitable for sensing applications¹. In this work, silica microspheres (spheres on the order of 250μm) are used as resonators. These resonators are coupled to a tapered optical fiber connected to an infrared laser. Using critical coupling techniques, resonant wavelengths (wavelengths of zero power transmission) are produced. The resonant wavelengths of the coupled system are dependent upon properties of the microsphere such as diameter and index of refraction. Conjugation of biological organisms to the sphere causes a small change in these properties and thus creates a shift in resonant wavelengths (free spectral range) which can be characterized and used as a sensor. This paper will discuss microsphere and taper fabrication, the tested functionalization process, and the effect conjugation has on the microsphere Q factors. Future work includes real time analysis of biological organism conjugation and bringing the sensor down to the chip sized scale.

This paper discusses ongoing research at Lawrence Livermore National Laboratory (LLNL) that investigates the effectiveness of spherical micro-resonators, coupled to a symmetrically tapered optical fiber, as a gas sensor. We will discuss silica-based microspheres and optimized tapered fiber coupling systems to detect greenhouse gases, i.e. CO₂ in this context. The coupling setup is designed to be portable and amenable to different controlled environments, from constrained and controlled geometries to open and flexible enclosures. 3D-printed spherical resonator and tapered-fiber holders were made to satisfy different requirements. We produced microspheres for absorption spectroscopy of targeted gas and fabricated tapers by HF etching, using an HF-resistant fixture for safer handling and reduced waste. Detection within loose enclosures was performed as a preliminary study, where we observed spectral shift and broadening in the cavity resonances induced by the gaseous environments. Optically coupled vacuum-tight vessels have been designed and built to understand environmental effects.

This study presents a time-stretched wavelength-swept laser source based on stretched-pulse mode-locking. A broadband semiconductor optical amplifier (SOA) technology is used as an optical gain element. The laser comprises a unidirectional ring cavity with matched positive and negative continuously chirped fiber Bragg gratings (FBG’s). One FBG generates a total positive dispersion of 454 ps/nm at 1275 nm and the other chirped FBG generates a total negative dispersion of -454 ps/nm at 1275 nm. A high-extension lithium-niobate intensity modulator (>30dB extinction at 1275 nm, 4.9 dB loss at maximum transmission) is driven with short pulses by a bit pattern generator providing approximately 0.235 ns full-width at half-maximum pulse profiles. These pulses are stretched, amplified, and compressed within the ring cavity, and the modulator pulsing is synchronized to a harmonic of the cavity round trip time. The laser output is provided from the cavity by a 25% coupler. The output light is amplified by another SOA. The laser source provides a sweeping range of approximately 90 nm centered at around 1275 nm at a repetition rate of ~5 MHz. This yields an estimated axial resolution of 8 μm in air.

A micro-optic bottle resonators constructed by azimuthal sculpting a pair of rings along the perimeter of a glass whisker is proposed. The structures are examined using a numerical solver optimized for the cylindrical symmetry of such resonators. The modal space and field profiles are computed as a function of ring spacing and demonstrates that multiple glass region confined states are available and operate similar to the well-known Whispering-Gallery-Modes. Additional computation results are presented when the structure is configured as an index of refraction sensor.

Beam profile engineering, where a desired optical intensity distribution is generated by phase shifting and/or amplitude changing elements, is a promising approach in various laser-related applications. For example, vector geometrical phase elements enable various flat special optical elements such as top-hat converters. We present a study on engineering efficient top-hat converters inscribed in the glass by femtosecond laser pulses. We start with an amplitude encoded top hat converter and demonstrate how its efficiency can be further increased by introduction of phase masks and by the polarization of the incident beam. Experimental verification of the concept is also presented.

Laser beam shaping technology nowadays requires as small diameter of the adaptive optics as possible. In our lab we usually control for laser radiation by means of bimorph deformable mirrors with a typical size of more than 50 mm. To fit the most of industrial and scientific applications the aperture of the corrector should be reduced because the use of extra optics instead makes the whole optical scheme more complicated and introduces extra distortions. But in a bid to reduce the size of the mirror we should care of the response of the mirror electrodes which obviously should not decrease drastically. Here we present 20 mm bimorph mirror with high density of electrodes which is manufactured using laser engraving technology to divide the electrode on the piezoceramic disc into a large number of the controlled sectors. The ability of laser beam formation by means of this mirror is discussed, the results are compared with the ones obtained using 50 mm bimorph deformable mirror.

We investigate the requirements for the pulse width and intensity of the pump beam, for the Fe:ZnSe lasing medium to reach threshold. The rate equation is solved for the time dependence of the population density, N₂ of the ⁵T₂ manifold which includes the upper level for the lasing transition.