bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of Atmospheric Turbulence Using a High Speed Curvature Sensing Camera
Authors: Takami Hideki , Kataza Hirokazu
Published: February 2023

Investigation of the properties of atmospheric turbulence which produce wave-front errors are essential to determine the number of control points and the control speed of adaptive optics system. The spatial properties are generally believed to be described by 5/3 law of Kolmogorov's turbulence theory. This has been experimentally verified in various manners1. On the other hand very few measurements of time evolution of the turbulence have been made, in spite of the importance for determining the control speed2.
Large Scale Deformable Mirrors with Hybrid Drivers
Authors: Ealey Mark A.
Published: February 2023

Many lessons were learned from building experimental deformable mirrors with many hundreds of actuators. The design of the next generation large aperture component is discussed in terms of those lessons and previously undisclosed developments which include a 28 volt actuator stack with redundant segments and a hybrid driver compatible with multiplexed operation.
Femtosecond single-pass optical parametric generator (OPG) for 1.38-1.56 μm with 35 MHz repetition rate
Authors: Südmeyer T. , Aus der Au J. , Paschotta R. , Keller U. , Smith G. R. , Ross G. W. , Hanna D. C.
Published: February 2023

Optical parametric generation (OPG) in a single pass through a χ(2) nonlinear crystal is a simple way to generate ultrashort pulses which are tunable in a broad wavelength range. In contrast to an ultrafast optical parametric oscillator, OPG does not require an oscillator cavity which is synchronized to the laser. However, the required pump intensities are much higher. For this reason, so far OPG experiments with ultrashort pulses have always required amplified pump sources, e.g. based on a mode-locked oscillator and a high-gain amplifier operated at a repetition rate of typically far below 1 MHz [1, 2]. Such pump sources lead to quite complex systems, and low repetition rates very much limit the obtainable average output power. Recent progress on high-power passively mode-locked all-solid-state lasers has enabled us to pump a parametric generator directly with a mode-locked laser, not using any amplifier system. In this way we obtained up to 0.5 W of average power in femtosecond pulses at 35 MHz repetition rate in the wavelength range of 1.38-1.56 μm using a periodically poled LiNbO3 (PPLN) crystal. The corresponding range of the idler is 3.03-4.06 μm.
Evaluating Color Appearance Using the OSA Uniform Color Scales Samples and a Color-Naming Method
Authors: Boynton Robert M.
Published: February 2023

Each color chip of the OSA Uniform Color Scales set (1) is intended to represent a color which, under the appropriate viewing conditions, is subjectively equidistant from its nearest neighbors in a 3-dimensional Euclidean space. To the extent this is so, the 424 chips of the set define -- and at the same time sample -- a space that is isotropic with respect to color differences. The three dimensions of the OSA space, called L, j, and g, permit the color chips to be labeled with triplets of values that can be positive or negative relative to 0,0,0, for which there is a chip intended to be a middle gray. L represents a lightness axis, ranging from very dark at the bottom to very light at the top. J and g are chromatic axes (roughly yellow(+)/blue(-) and green(+)/red(-) respectively); these are orthogonal to each other and to the L axis.
On the Role of Figural Organization in Perceptual Transparency
Authors: Beck Jacob
Published: February 2023

Metelli (1974, 1985) proposed a model of the intensity relations in perceptual transparency based on a physical model of transparency involving additive color mixture. Beck et al. (1984) reported four findings which suggest that a change in point of view is required. First, they showed that the relevant variable for the perception of transparency is the psychological variable of lightness and not the physical variables of luminance or reflectance. Second, they showed that physical models of transparency based on either additive or subtractive color mixture entail four constraints. However, only violations of constraints (i) and (ii) adversely affect judgments of perceptual transparency; violations of constraints (iii) and (iv) do not. Nonveridical perceptions of transparency occur when constraints (iii) and (iv) are violated. Third, there are simple and strong violations of constraints (i) and (ii). Transparency judgments, though reduced in number, still occur for simple violations of constraints (i) and (ii). Transparency judgments occur infrequently for strong violations of constraints (i) and (ii). Physical models of transparency fail to differentiate between simple and strong violations. Fourth, it is necessary .to distinguish between perceptual transparency occurring with and without constancy. Constancy occurs when the color seen through the transparent surface is seen to be the same as the color of the surface not overlaid by the transparent surface.
Color Constancy and Color Rendering: Concomitant Engineering of Illuminants and Reflectances
Authors: Brill Michael H.
Published: February 2023

Designers of lights and reflectances seek--among other things--to create environments in which interchanges of artificial and representative natural daylights produce no noticeable effect on the appearance (or at least recognizability3 of colored objects. The present paper discusses some aspects of cooperative design whereby lighting and reflectances reveal the reflectances to be color-stable under interchange of a repertory of lights which therefore can be said to have good color-rendering properties. Of course, the designer’s world ought not to be restricted to degenerate solutions such as grey reflectances under low-pressure sodium lamps, but rather should contain natural daylights and reflectances.
Can Clinical Judgements be Used as Indices of Satisfactory Colour Rendering of Flourescent Lamps in Hospitals?
Authors: Hill Adrian R. , Reeves B.C.
Published: February 2023

With the development of ever more efficient light sources, there is
increasing interest in the evaluation of the colour rendering
properties of new lamps in situations where colour judgements are
critical. One such situation is in hospitals where doctors may often
be required to make clinical decisions based upon the colour
appearance of a patient's skin. However, it is important that
financial savings to a hospital should not be made at the patient's
expense. Consequently it is necessary to assess the differences in
colour rendering tolerated by doctors in clinical situations.
The Computational Approach to Colour Reproduction
Authors: Cowan William B.
Published: February 2023

We can now manipulate images pixel by pixel using computer graphics techniques. This ability eliminates many of the technical difficulties associated with colour reproduction. The outstanding problem is to decide what colour we wish a given pixel to be, a colour appearance problem. This review addresses questions of this type raised by a recent project to do practical digital colour reproduction.
Miniature integrated SHG green laser
Authors: Masuda Hisashi , Maeda Fumisada , Oka Michio , Kaneda Yushi , Sugiura Minako , Kubota Shigeo
Published: February 2023

Diode-pumped intracavity frequency doubled Nd:YAG lasers have been intensively investigated. Low noise characteristics of such a laser as well as its shorter wavelength than conventional laser diodes are attractive features for the higher density optical disk applications.1
II-VI Blue-Green Diode Lasers
Authors: DePuydt J.M. , Haase M.A. , Qiu J. , Cheng H.
Published: February 2023

Injection lasing in the wide band gap II-VI semiconductors was achieved for the first time in our laboratory in April, 1991.1 Since then considerable effort has been made toward understanding the properties of these laser diodes and constituent materials as well as making progress toward the development of viable devices. We have demonstrated room temperature, pulsed operation in devices with emission wavelengths from 508-535nm. More recently, we have achieved cw operation at 77K. In this paper we will describe the operating characteristics and fundamental parameters of our blue-green laser diodes.
High efficiency frequency doubling around 430nm
Authors: Polzik E. S. , Kimble H. J.
Published: February 2023

Potassium niobate (KNbO3) is known for its high nonlinear coefficient which together with the increasing quality of crystals available makes it a very attractive candidate for frequency doubling into the blue. Previous work has demonstrated that frequency doubling in an external cavity is a good alternative to doubling within the laser cavity since it allows for independent optimization of the laser and doubling cavities. With reference to KNbO3 in an external cavity, 40mW of blue output was obtained by doubling a diode laser,[1] while 154mW was achieved by nonlinear mixing of diode and Nd:YAG emission.[2]
High peak and average power diode-pumped NYAB green laser
Authors: Stone R. E. , Wang S. C.
Published: February 2023

The self-frequency-doubling crystal Neodymium Yttrium Aluminum Borate
(NYAB) is an ideal candidate for diode-pumped compact green laser
system. Because it has several unique features including broad and
strong absorption at the diode laser wavelengths, high nonlinear
optical coefficient, high damage threshold, and low luminescence
quenching effects. Besides it has shorter fluorescence lifetime than
Nd: YAG crystal that allows the laser to operate at relatively higher
repetition rate. The operation of diode-pumped NYAB at green
wavelength 531 nm has been reported by us and several groups
recently.1-3 However, the reported green laser
output powers are relatively low due partly to the poor quality of the
quality of the crystal which is still under development. Besides the
relatively strong absorption at green wavelength is also considered to
be a contributing factor. We report here the achievement of the high
power output obtained from a NYAB crystal under both cw and Q-switched
operation at room temperature.
KTP segmented waveguides as concurrent Bragg reflectors and second harmonic generators
Authors: Roelofs M. G. , Bindloss W. , Suna A. , Lee J. D. , Bierlein J. D.
Published: February 2023

A periodic modulation of optical nonlinearity by means of ferroelectric domain reversal has led to the generation of blue light by quasi-phase matching in waveguides of, e.g. lithium niobate1,2, lithium tantalate3,2, and potassium titanyl phosphate (KTP)4. When the linear optical constant (index) is also periodically modulated along the propagation direction, these waveguides may serve also as distributed Bragg reflectors5,6. The back reflection of light in a narrow band of wavelengths, subject to the Bragg condition, has been utilized to stabilize a diode laser pump, forcing it to oscillate in a narrower band of wavelengths suitable for second harmonic generation.
Characteristics of KTiOPO4 Waveguides Up to High Power Densities
Authors: Morris P. A. , Brown J. B. , Bierlein J. D.
Published: February 2023

KTiOPO4 (KTP) possesses a unique combination of properties making it useful for a variety of bulk and waveguide nonlinear optical applications.1 Spatially well-defined waveguide and domain structures are readily produced in crystals through ion exchange techniques.2,3 Highly efficient second harmonic generation into the blue wavelength range is achieved in KTP using quasi-phase matching in segmented/domain-inverted waveguides.4 Recently, results have been reported indicating that there are power limitations or instabilities which occur when quasi-phase matching into the blue using KTP.5 However, the transmission characteristics of conventional KTP waveguides have been reported to be stable at 514 and 488 nm to high powers.6
The Use of Air-Cooled Argon Ion Lasers in Automated Genetic Analysis
Authors: Kronick Mel N.
Published: February 2023

Significant advances in our understanding of biological function and dysfunction have been made possible over the last several years by the development of techniques to sequence and analyze DNA. Automation has been introduced to increase the speed and accuracy of such sequencing and analysis and to make the processes less laborious and less costly. Today, the method of choice of such automation utilizes laser excitation to detect, in real time, fluorescently labeled DNA fragments as they are electrophoretically driven through a separating gel medium (1). The fluorescence-based technology for analysis has been applied to many current problems in medical and biological research with great success. It is now routinely used in hundreds of laboratories worldwide to sequence DNA in a wide variety of biotechnology research projects including programs such as the Human Genome Initiative. Applications to the mapping and diagnosis of genetic disorders as well as to the use of DNA for forensic purposes have also been amply demonstrated (2,3). An even wider acceptance of the technology has unfortunately been significantly inhibited by its high price.
Thermal Characterisation of A II-VI Blue Semiconductor Laser
Authors: Drenten R.R. , Marshall T. , Gaines J. , Petruzzello J.
Published: February 2023

After proper p-doping in ZnSe became possible, several authors have reported on lasers in the II-VI semiconductor system [1,2]. The first results were obtained using a pulsed power supply and at liquid nitrogen temperature. Steady progress has been made since then, but one of the main problems is still the electrical contact to the p-doped semiconductor. The generally used metal contact acts as a reverse-biased Schottky junction. The breakdown voltage is of the order of ten volts, therefore considerable power dissipation takes place there, which makes CW room temperature operation difficult. In this work characterisation of the thermal behavior of such a II-VI semiconductor laser is presented. The results contribute to the understanding of the feasability of CW operation.
Enhanced Second-Harmonic Generation with a Periodically Poled Nonlinear Organic Copolymer
Authors: Sato Heihachi , Azumai Yuji , Seo Iwao
Published: February 2023

In second-harmonic generation (SHG) perfect phase-matching cannot be
essentially satisfied between fundamental and second-harmonic (SH)
waves for organic polymers or copolymers as done in inorganic
crystals. Thus, it is quite required to take the phase-matching by
some means. In order to overcome this disadvantage the inter-mode and
the Cerenkov radiative phase-matchings have been often adopted in a
slab or channel waveguide with mainly nonlinear optical (NLO) organic
and inorganic crystals. However, since the attainable SHG power
is necessarily limited, a periodic corrugation of the NLO
susceptibility χ(2) is induced into the waveguide for the
phase-matching or quasi-phase matching by using the technique of
domain-inversion in inorganic crystals.
Periodic Domaininverted Nonlinear Optics
Authors: Ito Hiromasa , Takyu Choichi , Ohashi Motoki
Published: February 2023

An e-beam method is developed for the fabrication of domain reversed volume grating in LiNbO3 and LiTaO3. Blue SHG experiment was performed to demonstrate high efficient nonlinear interactions. Periodic domain inverted structure has wide potentials for the various nonlinear optical interactions.
Stable and Efficient Generation of Green Light by Intracavity Frequency Doubling of Nd:YVO4 Lasers
Authors: Kitaoka Y. , Ohmori S. , Yamamoto K. , Kato M. , Sasaki T.
Published: February 2023

Compact laser sources of shorter wavelengths offer the potential for high-density optical recording, but they also require low noise and a high-power light beam (over 10 mW). It was recently reported that a continuous wave green laser diode (LD) of II-VI groups oscillated at the Nitrogen temperature and also emitted pulsed wave at room temperature.1 Nonetheless, further efforts are required for practical application of II-VI lasers.
Comparison of Yb, Ho Upconversion Energy Transfer in Different Fluoride Crystals
Authors: Zhang X.X. , Bass M. , Chai B.H.T. , Peale R.E.
Published: February 2023

Recently, there is a renewed interest in obtaining short wavelength solid state lasers through upconversion schemes. Yb sensitized upconversion energy transfer is specially attractive for this purpose because of the ability of high power InGaAs diode lasers to pump Yb. Yb, Ho upconversion energy transfer is relatively simple compared to upconversion involving other rare earth ions. Although a Yb sensitized Ho green laser has been realized at 77 K in BaY2F8 [1], no such lasing has been achieved at room temperature. In searching for a more suitable host for the room temperature Yb, Ho green upconversion laser we have carried out a systematic spectroscopic study on the Yb, Ho upconversion processes in BaY2F8 (BYF), KYF4 (KYF), and LiYF4 (YLF). Based on the detailed absorption, emission and fluorescence decay data, KYF is shown to be a promising host.
Controlling Chaos in an Intracavity Doubled Nd:YAG Laser
Authors: Roy Rajarshi
Published: February 2023

A Nd:YAG laser with an intracavity frequency doubling crystal displays irregular intensity fluctuations for certain ranges of operating parameters.1,2 Analysis of the laser system shows that these fluctuations are chaotic in nature, and that it is possible to operate the laser stably in selected parameter regimes.2,3 It has also been shown experimentally that dynamical control of such a laser system is possible, and that a variety of periodic waveforms as well as the unstable steady state can be stabilized through an appropriate feedback technique called occasional proportional control.4,5 In this technique, tiny kicks are given to the pump excitation, that depend in amplitude on the difference of the output intensity from a chosen reference level, and with a period related to the relaxation oscillation period. The laser may be maintained in a stabilized steady state over a wide range of pumping if a tracking procedure is used that makes suitable changes in the control circuit parameters as the pump level is altered.
Ho-Yb fluoride glass fiber for green lasers
Authors: Shikida A. , Yanagita H. , Toratani H.
Published: February 2023

Ho3+ upconversion emission at 543nm (5S2-5I8) is a potential candidate for realizing a red-diode pumped green laser. However, this emission is of three-level system, so that lower doping is needed to achieve lower lasing threshold. A long, low loss single mode fiber is usually adopted for this type of laser to obtain a sufficient pump absorption without much cavity loss [1]. To make a compact device, it is necessary to increase the pump absorption efficiency. Yb has been known as an effective sensitizer for Ho in many crystals when the diode emitting around 980nm is used for excitation [2]. We report effects of host glass composition and Yb sensitizer concentration on the Ho green upconversion emission and the pump power dependence of the excited population density for fiber lasers.
Resonator-enhanced frequency doubling in an extended-cavity diode laser
Authors: Kozlovsky W. J. , Risk W. P. , Lenth W. , Bona G. L. , Jaeckel H. , Webb D. J.
Published: February 2023

Compact, efficient, diode-laser-based blue light sources are useful for many applications including optical storage and laser printing. Blue light can be generated by frequency doubling the output of reliable, high-power 860-nm lasers in potassium niobate. The Second Harmonic Generation (SHG) conversion efficiency can be substantially increased by placing the nonlinear crystal inside of a resonator in order to increase the infrared intensity in the crystal.1,2,3,4 The build-up of a high infrared intensity and efficient generation of blue output requires precise frequency matching of the diode laser and the SHG resonator. Previously, electronic locking1 and weak optical feedback techniques2,3,4 have been used to maintain this frequency matching. Electronic locking has the disadvantage of requiring an optical isolator to prevent destabilization of the laser frequency by light scattered from the resonator. Weak optical feedback has the disadvantage of requiring electronic control of the phase of the optical feedback as well as precise control of the feedback amplitude.3,4 We describe the operation of an antireflection-coated GaAlAs diode laser in an extended laser cavity that contains the SHG resonator as an intracavity element. The use of an antireflection coating on the laser and strong optical feedback is intended to suppress coupled-cavity effects and produce stable operation of the laser at a single frequency that is resonant with the SHG resonator. With the extended cavity we have obtained blue output powers of up to 12.5 milliwatts.
Applications for Low Power Blue-Green Lasers in Flow and Image Cytometry
Authors: Hoffman Robert A.
Published: February 2023

Cytometry is a technology for analyzing specific characteristics of biological cells (cyto) using quantitative physical measurements (metry).
Revealing of the Domain-Inverted Grating in KTP Using the Nonlinear Talbot Effect
Authors: Buritskii K. S. , Chernykh V. A. , Dianov E. M. , Maslov V. A. , Shcherbakov E. A.
Published: February 2023

Alternating ferroelectric domains were created in LiNbO3, LiTaO3and KTP by various methods.
All-solid-state UV source using a single cavity resonant enhancement technique
Authors: Robertson A. , Ferguson A. I.
Published: February 2023

Coherent ultraviolet radiation has many applications in science and industry, including photochemistry, photobiology, high resolution spectroscopy, and as a pump source for optical parametric oscillators operating in the visible. The excimer and ion lasers generate UV, usually in continuous wave (cw) or pulsed operation. For nonlinear optical applications in which high peak powers are advantageous, cw mode-locked sources are increasingly being employed, and at UV wavelengths such devices are being developed through the exploitation of nonlinear frequency conversion techniques in a variety of optical materials such as beta-barium borate (BBO) and lithium triborate (LBO). Furthermore, novel resonator designs have been used to increase the efficiency and reduce the complexity of these UV sources.1 We report on an all solid-state source of CW mode-locked UV radiation at the third-harmonic of a Nd:YLF laser pumped by laser diodes.
Recent progress in visible light-emitting semiconductor lasers
Authors: Valster A.
Published: February 2023

The performance of (Al)GalnP visible light emitting semiconductor lasers has significantly improved over the last few years as the result of the introduction of strained quantum well (SQW) layers in the active region.1 Grown-in strain modifies the valence subband structure which results in a reduced density of states and an improved symmetry of states at the valence band maximum. Both lead to a considerable reduction in the threshold current density of the semiconductor laser. We have fabricated by low-pressure organometallic vapour phase epitaxy (LP-OMVPE) 1% compressively strained single QW broad-area lasers with a threshold current density of 240 A/cm2. The lasing wavelength is 675 nm. Gain guided 7 μm × 300 μm stripe lasers have threshold currents of 24 mA at room temperature and are lasing beyond 100°C. Lifetests of 4 different wafers at 70°C and 4 mW output power shows a projected median lifetime of 70,000 hours which demonstrates the excellent reliability of SQW visible lasers.
Annular resonators for diffusion cooled CO2-lasers
Authors: Ehrlichmann Dietmar , Habich Uwe , Plum Heinz-Dieter , Loosen Peter
Published: February 2023

Annular gain geometries provide large surfaces along with compact overall dimensions, which make them promising for compact high power diffusion cooled CO2-lasers (>1 kW). The large surface enables efficient heat removal from the laser gas by heat conduction (diffusion) to the discharge walls. Diffusion cooled systems do not need gas blowers as currently used for convectively cooled lasers. However, a suitable annular resonator has to be designed meeting the requirements of high beam quality and laser efficiency.
Efficient thermal management for passively cooled high power diode-pumped Nd:YAG lasers
Authors: Jackson Stuart D. , Piper James A.
Published: February 2023

Scaling the output power of diode-pumped solid-state lasers in general has involved side-pumped geometries incorporating a number of high power, quasi-cw diode arrays. An important design criterion for these devices is the management of the heat generated in the laser rod. However, a cooling system that did not depend on flowing water would have several advantages, including reduced size and complexity, no requirements for external water supplies or chillers, and no problems with water leaks.
Mobile gas sensor for remote detection of halogenated hydrocarbons
Authors: Dinges P. , Fiedler M. , Golusda E. , Lange R. , Lühmann K.
Published: February 2023

Presently, conventional techniques of atmospheric monitoring based on local air sampling suffer from one disadvantage: air quality (the concentration of trace gases in the atmosphere) is monitored only at specific locations, where the respective samplers are placed; consequently, strong spatial concentration variations may not be detected at all or merely as diluted and small. On the other hand, LIDAR (Light Detection And Ranging),1 the optical analogon of RADAR, offers the advantage of monitoring extended remote areas (from a single LIDAR sensor location) and allows concentration distributions of trace gases to be recorded in fairly short time. Thus, LIDAR is a well suited technique for environmental and industrial atmospheric monitoring (early warning).
Sea-surface lidar for wave-height spectrum measurements
Authors: Mikhalevich V.
Published: February 2023

The small-scale structure of the sea surface has received increased attention in recent years. This comes mostly from the necessity to study wave interactions in the ocean and to explain radar back scatter from the surface.
Influence of carrier transport on the turn-on delay in a separate confinement heterostructure quantum well laser
Authors: Greiner A. , Kuhn T. , Hillmer H. , Hansmann S. , Burkhard H.
Published: February 2023

We investigated theoretically the turn-on delay (t
on
) of a SCH-QW-laser biased above the threshold current density. The dependence of this delay time on the geometrical laser structure is important for high-frequency characteristics. In our model the single QW is shifted from the center of the waveguide layer (1017 cm−3 p-doped) towards the n- or p-doped cladding regions with a doping concentration of 1018cm−3 (see inset in Fig. 1). We performed a one-dimensional simulation of the carrier dynamics with respect to carrier transport based on a drift diffusion model, including the influence of Fermi–Dirac statistics1,2 and Poissons equation for the electrostatic potential. For the photon number we use a rate equation.3 Changing the boundary conditions for the electrostatic potential, we increase the injected current on a timescale of 1 ps. To obtain comparable results the power ratio P
on
/P
off
is kept constant, as well as the difference of the injection currents (j
on
–j
off
). Differential gain, transparency carrier concentration, and confinement factor are assumed to be equal for the three different structures. Figure 1 shows the light output power versus current density characteristics, revealing a change even in the stationary properties of the laser. This is a first hint that carrier transport becomes important. Looking at the response of the photon number we observe a significant dependence on the location of the QW. t
on
increases more than 20% if the QW is shifted towards the n-doped cladding layer and it decreases more than 20% due to the shift versus the p-doped cladding layer (see Fig. 2). The pulse shape was kept identical in all three cases. This allows us to compare the results.
Nd:LaF3 crystal lasers: cw, Q-switched operation and upconversion fluorescence
Authors: Shi Yuan , Poulsen Ove , Haugen Harold K.
Published: February 2023

There has been a great interest and extensive research in diode laser-pumped solid-state lasers in the past decade. Nd:LaF3 crystals have a long lifetime and broad absorption feature1 compared to Nd:YAG and Nd:YLF crystals. These are advantages for Q-switched laser operation. We report a Nd:LaF3 laser pumped by a 788-nm Ti:sapphire laser in cw and Q-switched operation. Upconversion fluorescence and the corresponding mechanisms are analyzed.
Passive mode-locking and dispersion measurement of a cw sub-100 femtosecond Cr4+:YAG laser
Authors: Tong Y. P. , Conlon P. J. , French P. M. W. , Taylor J. R. , Shestakov A. V.
Published: February 2023

The rapid development of ultrafast tunable solid-state lasers has extended to the near infrared with the demonstration of mode-locked Cr4+:Forsterite' and Cr4+: YAG lasers.2 Previously we reported the first ultrafast Cr4+:YAG laser, which was actively mode-locked with an acoustooptic modulator to yield 26 ps pulses." Subsequent refinements have reduced the pulse duration to 10 ps and we have also generated ~ 20 ps pulses using synchronous mode-locking. We now report on passive mode-locking of this laser medium. We have observed that, although mode-locking was achieved across almost the full laser tuning range (coating-limited to 1.37–1.58 μm), femtosecond operation was only possible above 1.49 μm. Following a measurement of the intracavity group velocity dispersion (GVD), we attribute this to the deletirious effects of water absorption lines.
The antiresonant Fabry–Perot saturable absorber (A-FPSA): saturation behaviour and operation in mode-locked solid-state lasers
Authors: Brovelli L. R. , Keller U. , Chiu T. H.
Published: February 2023

The antiresonant Fabry–Perot saturable semiconductor absorber (A-FPSA) has been used successfully as a nonlinear mirror to passively mode lock many different solid-state lasers with picosecond pulses from Nd:YLF and Nd:YAG lasers,1,2,3 and pulses as short as 90 fs from Ndrglass lasers.4,5 The A-FPSA is a low-temperature (LT) grown InGaAs/AlGaAs superlattice between two high-reflecting Bragg mirrors forming a high-finesse Fabry-Perot operated at antiresonance. The main advantages of the bitemporal A-FPSA are that the operation parameters, such as saturation intensity, insertion losses, and impulse response can be custom designed and adapted to the requirements of solid-state lasers, which always leads to self-starting and stable mode-locked operation. Typical drawbacks of semiconductor saturable absorbers—such as high insertion losses, low saturation intensity, and low damage threshold—are circumvented. We present detailed experimental investigations of the saturation behaviour of A-FPSAs and derive quantitative design rules, which allow for further optimization and adaptation of the device to other laser systems.
Gain media phase conjugators and self-adaptive solid-state lasers
Authors: Damzen M. J.
Published: February 2023

A presentation is made of recent work in 3-D saturable gain-gratings, produced by spatial hole-burning, as efficient, externally programmable and/or self-adaptive diffractive optical elements for application in gain-media phase conjugators and as a technology for versatile adaptive spatial, spectral, and Q-switching control of high-gain solid-state lasers. Description is to be mainly made of gain-gratings written by spatial hole-burning when coherent beams, at the lasing wavelength, interfere in a gain medium. Such 3-D gain gratings, which have a persistence for the upper-state lifetime of the gain medium, can be considered as volume gain holograms and the application of these adaptive grating devices can be considered as a type of dynamic "gain holography."
Growth of KNbO3 thin films on MgO by pulsed laser deposition
Authors: Zaldo C. , Gill D. S. , Mendiola J. , Eason R. W. , Chandler P. J.
Published: February 2023

KNbO3 crystals have numerous uses in electro-optical, nonlinear optical, and photorefractive device applications. However, their widespread availability is somewhat limited due to their cost and growth difficulties. For applications requiring waveguide geometries, further problems exist, as KNbO3 is not particularly suited to general fabrication techniques such as diffusion or ion exchange. Ion beam implantation has produced optical waveguides,1 and liquid phase epitaxy techniques2 prove successful, but so far, the technique of Pulsed Laser Deposition (PLD) has not been applied to thin film KNbO3 growth. We report here the results of waveguide growth using this technique.3
Multijoule TE CO2 laser using a novel magnetic-spiker sustainer excitation circuit
Authors: Bhadani P. K. , Tang Y. X. , Harrison R. G.
Published: February 2023

Recently we investigated several innovative approaches for electrical excitation of a TEA CO2 laser1-5 in order to overcome the limitations of existing discharge and switching technology and to provide an overall improvement in the laser performance. In particular, the magneticspiker sustainer excitation circuit has proved to be a power approach for efficient excitation of large volume pulsed CO2 lasers. This has provided high efficiency (15%) variable flat top long duration laser pulses (1–5µs), helium-free operation, and elimination of plasma switch (thyratron/spark gap) from the main discharge path, leading to the development of laser systems with a long operational lifetime and high reliability.
Design of phase gratings for applications in digital optics
Authors: Lüpken Hermann , Wyrowski Frank
Published: February 2023

In modern architectures of digital optics and material processing the splitting of an incoming light beam into an array of prescribed intensity light spots is of fundamental concern. The high efficiencies and the flexibility of the optical function encourage researchers in the design of diffractive phase gratings. The design problem is to find a phase transmittance or reflectance whose diffraction pattern contains an area of prescribed intensity. We call the diffraction pattern in this area the desired signal wave.
Optimization of distributed feedback lasers with chirped or pitch-modulated gratings
Authors: Olesen H. , Salzman J. , Pan X. , Tromborg B.
Published: February 2023

In order to achieve good dynamic single mode operation up to high output powers, distributed feedback (DFB) lasers with a discrete λ/4-shift, multiple phase shifts, and modulated corrugation pitch along the cavity have been considered.1-3 Haus and Shank have shown4 that a discrete λ/4-shift is the optimum way to achieve oscillation at the Bragg position and suppress unwanted modes. However, many groups have attempted to realize a distributed λ/4-shift, and the excellent performance of the corrugationpitch-modulated (CPM) laser2 shows that the DFB cavity can indeed be improved by varying the corrugation pitch along the cavity. Thus, the above-threshold performance of DFB lasers with different cavity designs deserves further study.
Gain-coupled DFB-lasers with a not saturable absorptive grating and an essentially simplified fabrication process
Authors: Johannes T. W.
Published: February 2023

Gain-coupled DFB lasers show an increased yield,1 a higher side mode suppression ratio,1 as well as a reduced sensitivity to external reflection as compared to index-coupled devices.2 As has been shown, the carrier dynamics in the corrugated absorptive grating may also significantly alter the device behaviour under direct modulation.3 Thus, a reduction of linewidth and chirp has been demonstrated.4
Systematic study of UV induced luminescence in Ge-doped optical fiber
Authors: Svalgaard Mikael , Nielsen Marianne Lund , Poulsen Ove
Published: February 2023

In recent years much attention has been directed to the mechanism and applications of UV induced refractive index changes in Ge-doped optical fibers. UV absorption bands at 190, 240, and 330 nm associated with Ge-Si wrong bonds are bleached by light of similar wavelength under emission of luminescence. The bleaching is accompanied by formation of other color centers, thus giving an overall rise in UV absorption, and consequently, an increase of the refractive index. Although the process is routinely used for writing index gratings in fibers, UV induced luminescence and index change are not well understood on a detailed level. Since it is difficult to monitor directly the induced index change we have conducted a systematic study of the associated photoluminescence.
Fabrication of sub-micron period gratings using an excimer laser irradiated phase mask
Authors: Dyer P. E. , Farley R. J. , Giedl R.
Published: February 2023

Irradiation of materials in close proximity to phase masks is currently of interest for fabricating micron-scale Bragg gratings in optical fibres and on planar optoelectronic components. Photo-sensitive silica fibres have been irradiated through a phase mask with a KrF excimer laser to form gratings by single and multiple pulses. We have recently used a silica phase mask with a suppressed zero order (<5%) and a period d = 533 nm to form sub-micron gratings on KrF excimer laser ablated polymers.3 Polymer films (Polyethylene Terephthalate and Polyimide) positioned within 300 µm of the mask were exposed at an average fluence of 25 mJ/cm2 for 1-5 pulses to form high- aspect ratio grating structures. Scanning electron microscope examination revealed two dominant microstructures having periods of 533 nm (Fig. 1) and 266 nm on the exposed surface.
Laser reactive ablation deposition of thin nitride films
Authors: D'Arma E. , Leggieri G. , Luches A. , Martino M. , Perrone A. , Majni G. , Mengucci P. , Luk'yanchuk B.
Published: February 2023

Lasers are used in materials processing from the beginning of the laser era, but their potentialities in this field have not yet been fully exploited and new laser- based techniques are emerging. The most recent one is laser reactive ablation (LRA) of thin films.1−4 In the LRA deposition method a solid support collects the material ablated by the laser irradiation of a target and reacted with an ambient gas. LRA has the advantage of being a singlestep process for synthesis and deposition of films.
Influence of the peculiarities of wavefront forming in real-time holographic interferometer upon the output of the interferometer
Authors: Gurevich S. B. , Konstantinov V. B. , Relin V. F.
Published: February 2023

The peculiarities of the wavefront forming in the Real-Time Holographic Interferometer are discussed. The wavefronts are formed by superposition of waves formed in a hologram by a reference beam and changed object beam. The features of the output image: intensity distribution, SNR and other parameters, are estimated depending on both the conditions of the forming of an initial hologram and the effect of the reference and object beams.
Bistable liquid crystal for high-resolution display application
Authors: Zöller A. , Abraham M. , Amato J. P. , Eidenschink R.
Published: February 2023

The filled nematics consist of small solid particles of pyrogenic silica dispersed in a nematic liquid crystal.1 Displays made with this material have bistable optical properties. A strong scattering state can be achieved by optical addressing using a laser diode. The laser light is absorbed by a dye in the liquid crystal or by an inorganic layer. Applying an AC voltage erases the written information and aligns the liquid crystal homeotropically into a transparent state. Both the scattering and the transparent state are stable in space and time. Local erasing is possible by applying a moderate voltage and directing a simultaneous laser pulse at the pixel to be erased. Grey scaling can be achieved by variation of the laser power during the writing process. For the writing process it is necessary that the laser power is absorbed. In transmission displays this is achieved by a dye, which is dissolved in the liquid crystal. For reflection displays a thin-film reflector-absorber has been developed.
Very short, low-loss multiquantum well GaAs/GaAlAs vertical directional coupler switch
Authors: Dollinger F. , Borcke M. V. , Klein W. , Böhm G. , Tränkle G. , Weimann G.
Published: February 2023

For application of directional couplers in optoelectronic integrated circuits, device length has to be reduced to about 100 µm to offer the benefits of high cutoff frequency and low space consumption. This can be achieved by vertical arrangement of the waveguides1 and exploiting the Quantum Confined Stark Effect for switching the device.2 Because of well known and highly reproducible material parameters, MBE grown GaAs/GaAlAs was chosen.
Multiple instruction multiple data optical computing with photothyristor smart pixels
Authors: Van de Velde T. , Thienpont H.
Published: February 2023

Recently a very promising active bistable vertical-to-surface transition electrophotonic device was developed to perform chip-to-chip optical interconnects—the PnpN photothyristors (Fig. 1). When used in the configuration of a differential pair, these multilayer III-V semiconductor (GaAs/AlGaAs) structures are capable of emitting a binary optical signal, when receiving a 250 fj optical input and controlled by a voltage cycle with period less than 70 ns.1
Observation of intrinsic optical bistability induced by self-focusing in a semiconductor-doped glass filter
Authors: Pereira F. , Salcedo J. R. , Belsley M.
Published: February 2023

Wherret et al.1 have derived a general condition for the existence of intrinsic optical bistability, stipulating that the absorption length of the sample, αL, must be less than 0.18. Nonetheless several research groups have observed optical bistability in samples with absorption lengths significantly above this limit.2 It has been suggested2 that the observed bistability is the result of an initial self-focusing of the incident beam brought about by thermal refractive index change which then induces a bistable effect in the final portion of the sample. If the focal length of the laser induced thermal lens is comparable with the sample thickness, then the reduction of the laser beam size could then induce bistability at a lower threshold in the final portion of the sample. We have carried a systematic test of this hypothesis, using a modified version of the Z-scan technique, on a commercially available semiconductor-doped glass filter.
High repetition rate optical pulse train generation using optical loop mirrors
Authors: Chan C. K. , Chen L. K.
Published: February 2023

In Ref. 1, a Mach-Zehnder interferometer is used to generate multiple pulses for CDMA encoders/decoders. When the optical pulse's linewidth is greater than the transfer bandwidth characteristics of the coupler used, the repetition rate of the pulse train may be increased. That is, single pulse input may result in multiple pulses output.
Passively Q-switched flashlamp-pumped ND:glass fiber-bundle laser
Authors: Griebner U. , Grunwald R. , Koch R.
Published: February 2023

Fiber-bundle lasers (FBL) are known as a special kind of solid-state lasers with spatially separated partial gain media.1,2 Because of the faster heat exchange in comparison to monolithic laser architectures, they allow to reach significantly higher pump levels as well as high pulse repetition frequencies (PRF). We report on advanced FBL schemes with solid-state Q-switching elements for the first time. Peak powers in the range of 100 kW have been produced.
Output saturation of the 2.71 μm laser in erbium-doped ZBLAN fibers
Authors: Bedö S. , Lüthy W. , Weber H. P.
Published: February 2023

The output saturation of the 2.71 μm laser in erbium-doped ZBLAN fibers was measured. The laser resonator was a Fabry-Perot configuration with a buttcoupled dichroic input mirror and the cleaved end of the fiber as output mirror, corresponding to an output reflectivity of 4%. The single mode fibers were pumped with up to 850 mW using a Ti:sapphire laser operated at 791 nm. The erbium concentration in the fibers was 1000 ppm, 5000 ppm, and 10000 ppm wt.
Influence of pyroelectric fields on the photorefractive effect
Authors: Buse K.
Published: February 2023

Photorefractive crystals enable many optical applications like image processing, signal amplification, and phase conjugation.1 In order to reach small response times, large light intensities obtained from Q-switched lasers are appropriate. We observe at high light intensities an additional photorefractive effect in electrooptic crystals.
Optical nonlinearities based on quenching and recovery of metastable EL2 defect in GaAs
Authors: Jarašiūnas K. , Sūdžius M. , Storasta J. , Gudelis V. , Bastienė L. , Vasiliauskas R.
Published: February 2023

Semi-insulating GaAs with its native mid-gap defect EL2 reveals optical optical nonlinearities of different kinds at short pulse excitation: (i) intrinsic ones based on nonequilibrium free carriers, and (ii) photorefractive ones due to space-charge redistribution. The metastable properties of EL2 open novel possibilities for direct optical modulation of quasi-Fermi level by resonant excitation and quenching of EL2 defect at low temperatures.1 This novel object—a light induced periodic structure of alternating areas with n- and p-type conductivity—needs deeper studies.
High-power diode-pumped Nd:YAG regenerative amplifier
Authors: Walker D. R. , Flood C. J. , van Driel H. M. , Greiner U. J. , Klingenberg H. H.
Published: February 2023

Solid-state laser systems capable of delivering both moderate average power and high peak power are of interest to the scientific and industrial communities, especially in applications requiring efficient harmonic wavelength conversion. We have developed a regeneratively amplified, mode-locked diode-pumped, Nd: YAG system presently capable of delivering 1 mJ in a 20 ps FWHM pulse at a repetition rate of 2 kHz.
Photoexcited carrier transport in InGaAsP/InP quantum well laser structures
Authors: Marcinkevičius S. , Olin U. , Fröjdh K. , Wallin J. , Landgren G.
Published: February 2023

We present first measurements of carrier transport in 1.55 μm InGaAsP/InP graded-index separate-confinement heterostructure (GRINSCH) multiple quantum well (QW) laser structures by means of time-resolved photoluminescence (PL). The high temporal resolution of the PL upconversion techniques enables explicitly monitor the carrier transport and draw conclusions about the transport mechanisms.
Refractive index changes of low temperature grown GaAs depending on its annealing history
Authors: Dankowski S. U. , Kiesel P. , Keil U. D. , Dykaar D. R. , Kneissl M. , Knüpfer B. , Kopf R. F. , Döhler G. H.
Published: February 2023

GaAs grown at low temperatures (LT-GaAs, 210°C-250°C) is known to exhibit very short carrier lifetimes (<1 ps)1,2 and semi-insulating behaviour after annealing (≈550°C). Therefore, this material is very appealing for both fabrication of excellent insulating layers in FETs and for extremely fast photoconductors.
Efficient diode-pumped tunable picosecond Cr3+:LiSAF laser
Authors: Falcoz Franck , Balembois François , Georges Patrick , Brun Alain
Published: February 2023

Compact diode-pumped solid-state lasers producing tunable picosecond pulses are very useful for scientific, medical, or industrial applications. Cr3+-doped Li-SrAl6, (Cr:LiSAF) has been demonstrated to be a very interesting laser material emitting like titanium sapphire in the near infrared, between 800 and 1000 nm.1 Moreover, its absorption band between 600 and 700 nm makes diode-pumping possible with recently developed high power AlGalnP red laser diodes.2,3
1.5 μm Room-temperature luminescence from erbium in oxygen-doped silicon grown by molecular beam epitaxy
Authors: Serna R. , Lohmeier M. , Vlieg E. , Polman A.
Published: February 2023

The indirect bank gap of Si precludes efficient light emission under electrical excitation. This makes Si impractical for optoelectronic applications. By doping the Si with erbium, characteristic Er intra-4f shell emission at 1.5 μm can be obtained at liquid nitrogen temperate.1 Earlier reports have shown that the luminescence intensity can be enhanced by the presence of low concentrations of oxygen.2,3,4