bluuebunny/crossref_metadata_2025 huggingface dataset:
Model for doubly resonant intracavity sum frequency mixing of two lasers
Authors: Kretschmann H. M. , Huber G.
Published: February 2023

Recently, special attention was taken to generating coherent radiation in the visible region around 600nm. Applications in medicine, display technology and other require those wavelengths that, due to absence of powerful fundamental lasers, cannot be obtained by frequency doubling. Several alternative methods were proposed. One promising method is doubly resonant all intracavity sum frequency mixing1 where more than 200mW of coherent radiation at 618nm were demonstrated. A numerical model for the mixer performance was proposed by Souma et al. in 1990 by solving the coupled rate equations. This model predicts the dynamical performance of the mixer, unfortunately it is quite complex. Since usually a continuous wave operation of the mixer is preferred, a simpler approach can be sufficient. Therefore, a theoretical model for continuous wave intracavity sum frequency mixing of two independent lasers inside a doubly resonant mixing resonator similar to the theory of intracavity second harmonic generation from Smith2 was developed.
Spectroscopy of Rare-Earth Doped Perovskite Phase Strontium Lanthanum Aluminate
Authors: Mosses R. W. , Wells J.-P. R. , Han T. P. J. , Gallagher H. G. , Yamaga M.
Published: February 2023

Strontium lanthanum aluminate (SrLaAlO4) belongs to a wide family of compounds with the general formula ABCO4 (where A denotes an alkaline earth cation: B denotes Y. Sc or a trivalent rare earth element and C denotes Al, Ga or a transition metal ion). This material crystallises in the perovskite phase, with tetragonal K2NiF4 structure having space group 14/mmm. The structure is composed of CO6 layers in the ab plane. The C cations are surrounded by six oxygens and sit in slightly distorted octahedral sites. Between these layers, the A cations and trivalent B cations are randomly distributed in nine co-ordinated sites of C4v symmetry. The random distribution of Sr2+ and La3+ ions leads to a structural disorder that causes inhomogeneous broadening of the spectral lines of rare-earth ions doped into these crystals.
Line Parameters Investigation of Carbon Dioxide in Air Using Difference-Frequency Infrared Spectrometer
Authors: Chen W. , Mouret G. , Bouher D.
Published: February 2023

For spectroscopy and atmospheric monitoring of trace gases applications which require a continuous-wave (cw) coherent tunable source, infrared (IR) wavelength range can be covered by two principle technologies: (1) lead-salt; (2) nonlinear frequency conversion. The former operates mostly at the temperature below 77 k (for 4.2-15 μm using diffused-junction homogeneous structure ) or up to 120 k (for 3-10.5 μm with double heterostructure) with typical output power of ~100 pW and tuning range per diode of ~100 cm-1. Based on nonlinear frequency mixing of two lasers in a crystal, difference-frequency generation (DFG) can be realized for the IR region: 3-9 μm with AgGaS2 and 9-16 μm with GaSe [1-2]. As an alternative to diode lasers, DFG IR sources offer large spectral tunability, ultranarrow linewidth, and moderate output power of 1-50 μW.
Photorefractivity of CdTe:Ge at 1.06 and 1.32 μm
Authors: Shcherbin K. , Oaouiov S. , Poplavko P.
Published: February 2023

CdTe is studied intensively as promising material for the real time holographic recording in the near infrared because it ensures the largest gain factor as compared to the other photorefractive semiconductors. In this report we present the results of characterisation of photorefractive germanium doped CdTe crystals grown in different Ukrainian laboratories and compere the results with that known for vanadium doped CdTe [1].
Photorefractive Effect in Copper-Doped LiNbO3 Waveguides
Authors: Kostritskii S. M. , Moretti P.
Published: February 2023

Photorefractive waveguides (PRW) are of prime interest for applications in integrated optics such as optical switching, resonant filtering or holographic memories. Therefore, investigations are to date extensively increasing to search new efficient methods of PRW’s fabrication Among the potential optical materials, lithium niobate (LiNbO3) has been subjected to extensive development, especially because crystals of good optical quality are commercially available. Comparatively to other known and mostly used methods of PRW’s elaboration in LiNbO3, the very new method of combined proton and copper exchange seems to present some interesting advantages [1,2]. This ionic exchange process enables to control easily and precisely the photorefractive response parameters since the copper concentration as well as the ratio Cu+/Cu2+ can be varied gradually in a wide range [1]. Moreover, it allows to reach an extremely high holographic sensitivity [2]. However, an undesired feature of the proton-exchanged waveguides is that the electrooptical coefficients are reduced significantly [2]. In contrast, no degradation of the latter is observed in ion-implanted waveguides [3]. Therefore, to elaborate the LiNbO3 waveguides with improved photorefractive properties, we have used a new two-step techique : First, the optical waveguides are formed by implantation of He+-ions at room temperature under a fluence of 2×1016 ions/cm2 and with an energy of 1 MeV, and second, the photorefractive sensitivity of the waveguides are increased by using the combined proton and copper exchage process, but conducted in specific conditions, i.e. when the proton exchange is minima, not sufficient to induce both an essential degradation of the electrooptical effect and a marked change of the effective refractive index.
Analysis of the three valence model of photorefraction in rhodium-doped barium titanate
Authors: Corner L. , Damzen M. J.
Published: February 2023

The three valence model of photorefraction was first proposed by Buse and Krätzig [1] and applied to rhodium-doped barium titanate (Rh:BaTiO3) after Kröse et al. found three charge states of rhodium present in this material [2].
Distributed feedback laser with combination of gratings self-induced in Nd:YAG amplifier and saturable absorbers
Authors: Antipov O. L. , Kuzhelev A. S. , Zinov’ev A. P. , Fedin A. V.
Published: February 2023

In the recent years self-starting laser systems with the cavity based on gain gratings have been demonstrated [1,2]. In this report we present new results of our investigation of a Nd:YAG laser with cavity formed with participation of population gratings (PGs) induced in the laser crystal as well as in the saturable absorber (Li:F or Cr4+ :YAG) by generated beams themselves.
SBS gain measurement in xenon near critical point
Authors: Buyko S. A. , Dolgopolov Y. V. , Dudov A. M. , Eroshenko V. A. , Kochemasov G. G. , Kulikov S. M. , Novikov V. N. , Shkapa A. F. , Sukharev S. A. , Zykov L. I. , Scott Andrew M.
Published: February 2023

SBS parameters in xenon in the density range of 0.3 g/cm3 < ρ < 1.82 g/cm3 and at temperature 292.5 ± 0.1K were examined experimentally. It was shown that in the density range from 0.3 g/cm3 up to 0.6 g/cm3 SBS gain increases achieving the value of g ≈ 140 cm/GW. In the density range from 1 g/cm3 up to 1.5 g/cm3 SBS gain decreases down to the value g ≈ 43 cm/GW due to anomalous decrease of phonons lifetime (τph ≈ 10 ns at the density 1.5 g/cm3). When the density increases above the value 1.5 g/cm3 SBS gain increases again achieving the maximal value g ≈ 160 cm/GW at ρ = 1.82 g/cm3.
Numerical Simulation of the Time Response of a Total Internal Reflection Self-Pumped BaTiO3 Phase Conjugate Mirror
Authors: Limeres J. , Carrascosa M.
Published: February 2023

Photorefractive phase conjugate mirrors have been widely investigated in the past years. In particular, self-pumped phase conjugators are specially usefull for technological applications because of their self alignment capabilities and compactness.
Electric Field Selectivity of Reflection Volume Holograms in LiNbO3
Authors: Petrov M. P. , Shamray A. V. , Petrov V. M. , Ioffe A. F.
Published: February 2023

The Bragg diffraction conditions in volume photorefractive holograms can be satisfied or violated by changing the refractive index. This can be achieved by applying the external electric field (Eo). The electric field selectivity (EFS) is characterized by the magnitude of variations in the applied electric field when the diffraction efficiency goes from the maximum to its first zero.
A model for feedback-stabilization in sillenites
Authors: Kamenov V. P. , Sturman B. I. , Frejlich J. , Ringhofer K. H
Published: February 2023

When recording phase volume holograms in photorefractive crystals, stabilization is often desirable so that the external conditions are constant during recording. A method of stabilization by using phase modulation in a feedback loop has been developed by Frejlich and Kamshilin. The method has been applied to LiNbO3, yielding the surprising side effect that for a large range of experimental parameters a diffraction efficiency, η, of 100 % could be achieved.1 Experiments have also been performed in the sillenites.2 There such a large diffraction efficiency is of course not possible, but there is another welcome side effect: by changing experimental parameters the detuning frequency, Ω, between the signal wave and the pump wave could be given an arbitrary value. As a consequence, the resonance of diffraction efficiency and gain as a function of detuning, fundamental for all applications of sillenites, can be exploited in experiments which at the same time are run stabilized.
1D and 2D self-focusing in photorefractive BaTiO3 crystal
Authors: Andrade-Lucio J. A. , Iturbe-Castillo M. D. , Marquez-Aguilar P. A. , Ramos-Garcia R.
Published: February 2023

Self-focusing effects in photorefractive media has been observed in several photorefractive crystals. We report the first experimental observation of the self-focusing ability and ID soliton formation in a BaTiO3 crystal. In our experiments we used a 4.3x4x2.5 mm single-domain BaTiO3 crystal with silver electrodes in the 4x2.5 mm2 face. The c-axis was parallel to the applied electric field. The experimental set up was similar to that used in our previous investigations of soliton interactions [1]
Micro-Machining of Glass by Excimer Laser Ablation
Authors: von Alvensleben F. , Graumann C. , Wais J.W.
Published: February 2023

Micro-structuring of glass has been examined using UV radiation. The etch depth profile has been investigated. The limitations and possibilities for micro-structuring on glass has been found for the wavelengths of 193nm, 248nm and 308nm.
Efficiency enhancing for mask based laser structuring
Authors: Jasper K. , Berger P. , Hügel H.
Published: February 2023

Microstructuring with, for example, excimer lasers is going to become a well established tool for industrial manufacturing. For these lasers typical optical set-ups are based on a mask projection technique. In some applications, however, the mask transmission is very small due to a small ratio of the hole pattern area to the whole illuminated area of the mask. For instance, in electronic industries the vias that have to be drilled on high packed multilayer boards have an integral cross-section of about one percent of the mask’s area. To increase the process efficiency, the reflected part of the laser beam can be used to irradiate the mask several times by means of an adequate illumination system. Further, the quality of the laser-induced structures is determined by the homogeneity and the beam divergence on the target surface.
Production of Supported Carbon Nanoclusters at Laser Ablation of Foam Graphite
Authors: Kudryashov S.I. , Ionov S.G. , Zorov N.B.
Published: February 2023

Foam graphite is a new and perspective material for laser ablation applications possessing of very low (subcriticai) bulk density and high concentration of nonequilibrium chemically-induced structural defects (vacancies and etc.). It shows “black body” absorbance, very low transversal thermal diffusivity and sound velocity due to its “sandwich-like” structure of graphite crystallites. Equilibrium laser evaporation of the low-density foam graphite occurs in regular air gaps of its “sandwich-like” structure and thus critical state of carbon seems to be produced. The droplet-like structure of critical state has been predicted by theory of condensed matter state earlier. Therefore laser-induced carbon critical state seems to be intensive source of carbon nanoclusters.
Neutral and ion number density mapping of laser ablated titanium plasma plumes using spectroscopic and electrostatic probe techniques
Authors: Williamson T. , El-Astal A.H. , Martin G.W. , Doyle L. , Al-Khateeb A. , Weaver I. , Riley D. , Lamb M. , Morrow T. , Lewis. CLS.
Published: February 2023

Development of spectroscopic and electrostatic probe techniques for the quantitative characterisation of low temperature laser ablated plasma plumes are described. The titanium plasma plume is formed by KrF irradiation, incident on a rotating target at laser fluences of 2-6 Jem−2 with a spot size 1.4 mm x 1.4 mm. A collimated, short pulsed, tunable dye laser at a set delay time, between 500ns - 2µs, is used to spatially and temporally probe the plasma plume in a direction parallel to the target surface (i.e. in x-z plane). For a plasma under-going self-similar expansion, the observed absorbance values A(ΔλS, z) are related to the corresponding absorber number densities N(x, z) within the (x-z) plane by (1) where f is the absorption oscillator strength, t is the probe delay time and ΔλS is the dye laser detuning from line centre wavelength λ0 of the transition.
Backside-laser annealing of silicon at low temperature
Authors: Antonova L.Kh. , Bayazitov R.M. , Galyautdinov M.F. , Grötzchel R.
Published: February 2023

Laser annealing of semiconductor layers by irradiation directed to the backside of the substrate is promising technique for modification of implanted layers and semiconductor structures. This technique allows to recrystallize the buried layers without disruption of the surface. However, the using of the industrial lasers with λ=1.06 µm for the backside annealing of silicon structures is ineffective, due to the screening of the powerful irradiation by the silicon substrate.
Comparison of weld quality with normal and 30° incident laser beams
Authors: Ng Eng S. , Watson Ian A.
Published: February 2023

The thermal cycle during laser welding of high carbon steels typically has a rapid cooling rate of about 104 K/s; in high carbon steels this results in a microstructure comprising ferrite matrix and hard martensite colonies [1,2]. Such high cooling rates can lead to deterioration of the weld quality due to hardness discontinuities between the fusion and heat affected zones. The hardness induced in the welded joint is dependent on the cooling process, itself being dependent on the laser parameters and weld geometry. The weld quality and hardness characteristics were improved by implementing an angular welding technique; this ameliorated the poor characteristics associated with rapid cooling. Two different angles of incidence (0°,30°) for welding were compared as were effects of the pulse length and pulse repetition frequency (PRF) on the mechanical and microscopic properties of the material. The gauge plates (0.88 mm) that were welded had a nominal composition of 0.85 wt % C, 0.4 wt % Si, 1.1 wt % Mn, 0.4 wt % Cr, 0.25 wt % V and 0.4 wt % W. The welding was done with Lumonic’s MS830 Nd:YAG laser, operating at 1.06 pm. The beam was delivered via a fibre optic system which was robotically manipulated. The welds were produced with a constant power of 200 watts and an argon shielding gas pressure of 5 x 104 Pa. The effect of varying the pulse length and PRF was quantified by measuring the hardness transverse to the weld direction, tensile strength, aspect ratio, weld volume formation rate and examining the phase transformation. Figures 1 and 2 show the hardness profiles of the weld for different pulse lengths and PRF, for the flat and 30° welding configurations, respectively. For both geometries, the hardness profiles decreased with increasing pulse length and PRF, however, the hardness gradients were lower for the 30° welding configuration. The hardness profile was dependent on the thermal distribution around the fusion and heat affected zones. Because of the rapidity of cooling for the normal weld geometry, the main weld region consisted of a martensitics structure [3], and the grain structure was coarser and less dense in the fusion zone. For the 30° welding configuration, a slower cooling rate was achieved, leading to a less brittle weld. The grain structure was typically fine and granular, and the structure was completely modified at the fusion zone. Additionally, a lower aspect ratio was obtained; this was due to the wider weld width produced with this geometry. Benefits of welding at 30° include: improved microstructure and reduced peak hardness profiles, greater weld width, higher tensile strength and greater weld volume formation rate. Ultimately, a higher welding speed was achieved.
Transmissive ZnSe Diffractive Optical Elements for High Power CO2 Material Processing Applications
Authors: Blair P , Jones D R , Villarreal F , Waddie A J , Ross N , Taghizadeh M R T , Baker H J , Hall D R , Shannon G , Johnston E , Steen W
Published: February 2023

The ‘bell profile’ provided by fast axial flow CO2 lasers is generally not optimum for surface treatment processes such as cladding, annealing and scabbling. Consequently, there is considerable potential for enhancing laser-based processing by using optical techniques to modify the natural beam to create process adapted beam shapes on the work-piece.
First overtone CO laser with suppressed fundamental band lasing
Authors: Ionin A.A. , Kotkov A.A. , Kurnosov A.K. , Napartovich A.P. , Seleznev L.V. , Turkin N.G.
Published: February 2023

First overtone (FO, ΔV=2) CO laser characteristics are studied both experimentally and theoretically. Fundamental band (ΔV=1) lasing is totally suppressed by intracavity optical filter. First overtone (FO) lasing in the experiment takes place between high vibrational levels (up to 30) corresponding to the spectral range of 2.7-3.6 µm. The e-beam controlled discharge laser parameters are varied in the following ranges: gas temperature 100-300 K, gas density 0.05 - 0.5 Amagat; 0 - 80% of helium and 60 - 97% [Illegible] nitrogen fraction in mixture CO:N2:He; the specific input energy up to 1 00 J/1 Amagat; pumping pulse length 20 - 1000 µs.
Corneal Surgery Procedures with an All-Solid-State Femtosecond Laser
Authors: Loesel F.H. , Juhasz T. , Horvath C. , Kurtz R.M. , Mourou G.
Published: February 2023

Recently, ultrafast lasers have received increased attention in a variety of biomedical applications, including refractive corneal surgery. The laser-tissue interaction with ultrashort laser pulses is based on laser-induced optical breakdown (LIOB), which results in the generation of a microplasma. Due to the expansion of the hot plasma a shock wave and a cavitation bubble are generated. As a result of this process, termed photodisruption, tissue in the focal volume is destroyed. LIOB can be achieved at significantly smaller threshold energies when using femtosecond laser pulses [1]. Furthermore, shock wave and cavitation bubble effects are reduced for the shorter pulses [2], allowing for minimally invasive and well localized corneal surgical procedures.
Excimer Laser Surgery of Cornea: Evaluation of Main Photochemical Target in Collagen
Authors: Nikogosyan David N. , Görner Helmut
Published: February 2023

In the past decade laser photorefractive keratectomy (PRK, surgery of cornea using 193 nm excimer lasers) has become a very popular clinical procedure for changing the refractivity of the human eye. However, PRK occasionally produces postoperative complications such as night vision problems, decreased contrast sensitivity, halos, redness, photophobia, glare, etc. Some of these complications were related to corneal irregularity which appears due to evaporation of tissue in course of laser irradiation via thermomechanical mechanism. Possible photochemical consequences of PRK have been neglected, though some of PRK-induced corneal alterations, e.g. epithelian haze, can be of a photochemical nature.
Diode laser activated protein solder for sutureless microsurgical repair of blood vessels
Authors: Trickett Rodney , Maitz Peter , Dekker Peter , Dawes Judith , Piper James , Lanzetta Marco , Owen Earl
Published: February 2023

We have developed a new sutureless technique to repair small blood vessels. This technique utilises a fully biodegradeable, protein solder that is laser activated to produce tissue welding. To demonstrate the effectiveness of this technique, the abdominal aorta of the rat (1.5 mm in diameter) was used as a model allowing surgery time, and recovery over a six week period to be compared with that of conventional microsuture repair.
Optimisation of H2-HCl-Ne buffer gas mixtures used in kinetically enhanced copper vapour lasers
Authors: Withford M. J. , Brown D. J. W. , Carman R. J. , Piper J. A.
Published: February 2023

Kinetically enhanced copper vapour lasers (KE-CVLs) have performance characteristics far exceeding those of conventional (elemental copper) devices [1,2]. For example, a 38mm diameter CVL normally producing only 65W when employing H2-Ne buffer gas mixtures produces >150W when kinetically enhanced. In addition, to the greatly increased repetition rate scaling characteristics of KE-CVLs, spatio-temporal gain characteristics are much more favourable for the extraction of high beam quality output from these devices.
Self-pumped phase-conjugate diode-pumped Nd:YAG loop resonator
Authors: Sillard P. , Brignon A. , Huignard J.-P. , Pocholle J. -P.
Published: February 2023

Self-pumped phase-conjugate (SPPC) gain media loop resonators present attractive features including dynamic correction of intracavity phase aberrations, and high extraction capabilities [1]. High-gain diode-pumped Nd:YAG amplifiers, because of their compactness and their high efficiencies, offer attractive potential for use in such resonators.In this paper, we present for the first time a SPPC diode-pumped Nd:YAG loop resonator operated in both injected and self-starting versions.
All-Fibre Frequency Shifters, Modulators and Switches
Authors: Russell P St. J. , Birks T.A.
Published: February 2023

Many all-fibre components already exist, such as multilayer mirrors (Bragg gratings), wavelength-sensitive beam splitters (tapered fibre couplers) and all-optical diode-laser-pumped lasers and amplifiers (by rare-earth doping of the core). Other desirable all-fibre components include electro-optic and acousto-optic modulators. These devices can be used as tunable filters, variable power dividers, frequency shifters and routing or packet switches They have a multitude of applications in telecommunications, sensing and lasers.
Extinction Ratio of A Three-Stage Wavelength Shifting Module Using Cross-Gain Modulation in Semiconductor Optical Amplifiers
Authors: Sohn Manjin , Park Heuk , Hwang Wol-Yon , Hong Hyun-Ha
Published: February 2023

Wavelength shifters allow for dynamic routing and wavelength reuse in wavelength-division-multiplexed (WDM) optical networks and switching systems. Several wavelength shifting schemes have been proposed, including cross-gain modulation, cross-phase modulation, and four-wave-mixing in a semiconductor optical amplifier. The cross-gain modulation method provides high conversion efficiency and a wide shifting range. However, the extinction ratio is significantly degraded upon upshifting. Recently, a two-stage wavelength shifting module by parallel pumping was demonstrated which enhances the extinction ratio[1]. To use the module in WDM-based photonic switching systems, its reversed output waveform should be reversed again by cascading one more wavelength shifter before or after the module (Thus three-stage). This additional stage could degrade the overall extinction ratio. We investigated the extinction ratio performances for three wavelength shifter schemes that employs cross-gain modulation.
Generation of binary optical dot streams in a liquid crystal device
Authors: Iino Yoshiki , Davis Peter
Published: February 2023

Development of future parallel communication systems demands technologies for generation, storage and manipulation of complicated optical beam patterns. Use of self-organizing spatial phenomena in self-modulating optical devices may be an effective approach. Experimental studies of bistable spatial memories using spatial light modulators [1,2] have shown spatial coupling is significant for the stability and resolution of light dots, and also can give rise to complex spatial patterns, including localized structures.
Multiplexed holographic storage in Ge-doped silica glasses
Authors: Berger Naum K. , Bekker Alexander , Fischer Baruch
Published: February 2023

High density storage is a major need in the rapidly developing area of information technology. While the telecommunication traffic in fiber optic networks goes beyond tens of Gb/s and even reaches Tb/s in single fibers (using WDM), the most capable optical recording methods lag behind. Holographic recording and storage of information in thick media is an attractive way to increase the storage capacity with short access time and high retrieving rates. This is facilitated by the possibility to use the whole volume of the material and the angular or wavelength multiplexing capability. Most of the effort in this direction is done by using photorefractive crystals, such as LiNbO3. There, several methods were developed to fix and store information.
Triple-clad Fibers for Lasers and Amplifiers
Authors: Tosin P. , Lüthy W. , Weber H.P.
Published: February 2023

A novel design of the refractive index profile for cladding-pumped fiber lasers and amplifiers has been developed and experimentally realized (cf. Fig. 1). The core (1) consists of pure silica and is doped with rare earth ions only. The light guiding in the core is provided by a depressed-index cladding (2) which is thick enough to suppress energy transfer from the core to the second cladding (3). The second cladding has almost the same index as the core as it consists of pure silica. A jacket with a low refractive index serves as third cladding (4). This leads to an interface with a high numerical aperture to guide the pump light. The single mode core has a low numerical aperture to allow for an increased diameter. This is advantageous for the absorption of pump light from the cladding, an increased energy storage capacity in the upper laser level for Q-switched systems and a reduced intensity in the core for high power applications. Since the core can be manufactured without index-raising dopants, the design also offers low intrinsic losses.
Grin Single Crystal Fibres
Authors: Renwick E K , MacDonald M P , Ruddock I S
Published: February 2023

During the past two decades, crystal fibres of many materials have been produced by the Laser Heated Miniature Pedestal Growth technique for a very wide range of applications This paper describes altering the refractive index of lithium niobate fibres by the out-diffusion of lithium oxide [1] to obtain fibres with radial extraordinary refractive index gradients. They have potential uses in sensing, sample excitation and as miniature in-line polarisers.
Fabrication and optimisation of waveguides in lithium niobate by differential etching following spatially selective domain inversion
Authors: Barry Ian E. , Ross Graeme W. , Smith Peter G.R. , Eason Robert W.
Published: February 2023

Lithium niobate is extensively used in a wide range of applications, due to its favourable electrooptic, acousto-optic, piezoelectric, elastic and photorefractive properties. The ability to engineer precisely controlled and very smooth structures has applications in lateral guidance such as waveguides and modulators, for multiple arrays in photonic bandgap structures and for surface acoustic wave devices such as filters and time delays.
Stable and Transient Colour Centers in YAlO3-ND Laser Crystals
Authors: Matkovskii A. , Durygin A. , Suchocki A. , Sugak D. , Wallrafen F.
Published: February 2023

The result of investigation of the UV, gamma irradiation, annealing in air (700-1300 K) and N2+H2 gas mixture (1700 K) on optical and lasing properties of Nd-doped YAlO3 (YAP-Nd) laser crystals are presented The crystals were grown by the Czochralski technique from iridium crucibles in 98% Ar+2% O2 atmosphere.
Beam-shaping technique for high brightness with high-power diode laser arrays
Authors: Baumann M. , Röhner M. , Du K.M. , Loosen P. , Poprawe R.
Published: February 2023

Because of the asymmetric emission characteristics of high-power diode laser bars, beam shaping is essential for coupling the light into a fibre. Preservation of the high brightness is the crucial point for minimum core diameter and NA.
GaAs VCSELs at λ = 780 nm for short distance polymer optical fiber data links at 2.5 Gb/s
Authors: Schnitzer P. , Grabherr M. , Jäger R. , Michalzik R. , Schmid W. , Ebeling K.J.
Published: February 2023

Visible, red emitting vertical cavity surface emitting lasers (VCSELs) [1] in the wavelength regime between 650 and 780 nm are very attractive light sources in low cost optical interconnects with on polymer optical fibers (POFs). We have fabricated GaAs-based 780 nm emission wavelength VCSELs using solid source MBE and p-type Carbon doping. Single layer 30 nm thick oxide apertures provide current and optical confinement. We employ 120 μm core diameter POF (Toray PGR-FB 125) because conventional POFs have core diameters between 0.25 and 3 mm making them impractical for high density optical interconnects with transmitter and receiver array pitch sizes of 250 μm or less [2].
Nanochannel Glass Photonic Bandgap Optical Limiting in the Visible
Authors: Campillo A. J. , Tonucci R. J. , Lin H-B.
Published: February 2023

Structures possessing a periodically modulated index of refraction with a pitch comparable to the wavelength of light are called photonic band gap materials. Light waves interact within these in a manner analogous to that of electrons within semiconductor crystals. Recently1, two-dimensional photonic bandgap behavior was demonstrated in the visible using nanochannel glass. In the present study, an effective limiter for the visible is realized by incorporating a thermal nonlinear liquid, consisting of an absorbing dye, nigrosin, dissolved in a solution of ethanol and toluene contained within the nanochannel capillaries2. We observe nonlinearly induced transmissions of less than 0.003, a significantly better value than obtained using either a defocusing or a hybrid incoherent scattering/defocusing geometry with comparable nonlinearity.
SBS-Compressed FT-limited laser pulses tunable in wavelength and duration (200 - 2000 ps)
Authors: Neshev D. , Velchev I. , Schiemann S. , Hogervorst W. , Ubachs W.
Published: February 2023

With the use of Fourier-transform (FT) limited laser pulses structural and dynamical information can be retained from gas, liquid and solid-phase samples, in principle both from time domain and frequency domain measurements. In many cases it is, however, practical to reduce the bandwidth such that the relevant spectral structures are resolved, and then use the resulting temporal response of the optical pulses to derive dynamical information on the spectrally resolved structures. Using a wavelength-tunable pulsed-dye amplifier, delivering FT-pulses of 5 ns, and pulse compression in a simple two-cell setup (filled with methanol) the resulting pulse duration could be varied in the range 400 - 2000 ps (see Fig. 1). Pulse compression is established by the process of Stimulated Brillouin Scattering (SBS). The resulting pulse duration is governed by the power density of the incident beam, which can be varied by the changing beam diameter. From spectral and time domain measurements it is demonstrated that in all cases ΔvΔr ≤ 1. For all measurements the SBS-conversion efficiency was >80%.
Advanced Laser Imaging Techniques in Medical Diagnosis
Authors: Cubeddu R. , Pifferi A. , Taroni P. , Valentini G. , Canti G. , Lindquist C. , Andersson-Engels S. , Svanberg S. , Wang I. , Svanberg K.
Published: February 2023

Fluorescence images, based on the emission of endogenous or exogenous fluorophores, are being investigated for cancer diagnosis. Several photosensitizers, presently studied for the Photodynamic therapy of tumors, localize in neoplastic tissues more than in healthy surrounding ones and are fluorescent. Therefore, they are also suitable markers for diagnosis. A non-invasive diagnostic procedure calls for sensitizer doses much lower than the therapeutic ones. In such a condition, the exogenous fluorescence is very faint, and can be overcome by the natural tissue fluorescence. The enhancement of the signal to noise ratio can be achieved using either spectral filters (multicolor imaging) or a time gated acquisition. Multicolor imaging is based on the acquisition of three spectrally different images, one in the red region, which mainly collects the exogenous signal, one in the green-yellow region, which accounts for natural fluorescence, and one in the blue region, for normalization purposes. A pseudo-image is then calculated using a suitable mathematical algorithm.
Two-Photon Excited Fluorescent Imaging of Complete Dental Samples
Authors: Girkin J.M. , Burns D. , Whitters C J , Hall A F
Published: February 2023

The early and reliable detection of tooth decay is very important in the modem dental practice. Sufficiently early detection of decay will enhance the potential for healing through the use of fluoride and a reduction in sugar intake; thereby reducing the need for use of a dental drill for cavity preparation. A range of optical techniques has been used to investigate the problem and it is known that the decayed tooth has different scattering and fluorescence properties from undamaged tissue. A number of centres around the world have investigated diagnostic systems using laser light at 488nm to excite the naturally occurring fluorophores as an aid to detection. The images from teeth have then been recorded using CCD cameras with some success.1 However, these techniques provide only a record of the surface area of the decay and some semi-quantative data relating to mineral loss. Information regarding the change in mineral distribution with depth is lacking. Such information may be crucial to the clinical management of early decay. In recent years the new technique of multi photon microscopic imaging has started to gain general acceptance in the biomedical arena. We have modified this technique and for the first time investigated the production of images from entire tissue samples including teeth.
Optical Coherence Tomography of Heterogeneous Tissue: Calculation of the Heterodyne Signal
Authors: Thrane Lars , Yura Harold T. , Hanson Steen G. , Andersen Peter E.
Published: February 2023

We present a new theoretical description of the Optical Coherence Tomography (OCT) technique for imaging through highly scattering tissue, e.g. human skin. The description, which includes both the scattering and the focusing of the light, is based on the extended Huygens-Fresnel principle first described by Lutomirski and Yura1 for beam propagation in the turbulent atmosphere.
Single-polarisation operation of injection locked fibre DFB lasers
Authors: Yamashita Shinji , Cowie Gregory J.
Published: February 2023

Optical fibre distributed-feedback (DFB) lasers using UV-written fibre Bragg gratings on Er3+:Yb3+ fibres feature single-frequency operation, thus are a promising technology for applications in optical fibre communications[1]. Most fibre DFB lasers, however, actually operate in two orthogonal polarisations as a result of polarisation independence in the fibre DFB resonator, which is not desirable for these applications. In this paper, we report single-polarisation operations of fibre DFB lasers using injection locking techniques, which are similar to those used for polarisation switching in He-Ne lasers[2].
Spontaneous interlevel emission from InGaAs/AlGaAs quantum dot structures
Authors: Vorobjev L.E. , Firsov D.A. , Shalygin V.A. , Tulupenko V.N. , Shemyakov Yu.M. , Egorov A.Yu. , Zhukov A.E. , Kovsh A.R. , Kop'ev P.S. , Kochnev I.V. , Ledentsov N.N. , Maximov M.V. , Ustinov V.M. , Alferov Zh. I.
Published: February 2023

Intersubband optical transitions of carriers in quantum wells (QW) have been investigated in detail, the infrared detectors, modulators and lasers have been developed. A study of interlevel carrier transitions in quantum dots (QD) opens the new prospects in designing the active devices for far infrared (FIR) region (λ >10μm).
Blue-green II-VI quantum well lasers
Authors: Uusimma P , Pessa M , Blood P , Auffret I , Cooper C
Published: February 2023

Blue-green laser diodes have been fabricated in the ZnSSe/CdZnSe quantum well system using structures grown on GaAs substrates in a dual-chamber MBE system. Short-lived room temperature CW operation has been achieved at a wavelength of 515nm with a threshold current density of 580Acm−2 and threshold voltage of 7V for a stripe-contact device 12μm × 1000μm with coated facets (90%/60%). The device had 1μm thick MgZnSSe optical confinement layers doped n = 8×1017cm−3 and 8×1016cm−3 respectively, ZnSSe waveguide core of total width 0.2 μm, with a centrally located 7nm wide CdZnSe quantum well. The structure was grown on an n-type substrate and was mounted p-side up. To reduce the operating voltage the devices used a new Te/Pd/Pt/Au contact technology and a ZnSe top contact layer grown by migration enhanced epitaxy. Studies of inverted (n on p) structures with GalnP and AlGaAs buffer layers, intended to reduce the internal barrier height at the Zn/Se heterojunction, showed these structures to have high forward voltages. Consequently only pulsed operation of these inverted lasers up to 250K was possible, with a threshold current of 600Acm−2.
Lasing and photoluminescence at T=77-650 K in MOVPE ZnSe/ZnMgSSe heterostructures
Authors: Yablonskii G. P. , Marko I. P. , Lutsenko E. V. , Gurskii A. L. , Kalisch H. , Heuken M. , Heime K.
Published: February 2023

ZnSe-based quantum well (QW) heterostructures are promising for vertical cavity lasers, optical switches, modulators, high density optical memory systems, full colour display panels. The ZnSe/ZnMgSSe/ZnMgSSe separate confined heterostructures (SCH) with single and multiple quantum wells (SQW, MQW) examined in this work were grown on GaAs substrates in a low pressure MOVPE reactor at a total pressure of 400 hPa and a growth temperature of 330°C, using dimethylzinc triethylamine adduct (DMZn(TEN)), ditertiarybutylselenium (DTBSe), ditertiarybutylsulphur (DTBS) and bismethylcyclopentadienylmagnesium ((MeCp)2Mg) as precursors. Optical properties of the structures were investigated over the temperature range T=78-650 K under the pulse N2 laser excitation (λ=337.1 nm, τ=8 ns, f=l kHz). The laser action was achieved up to T=577 K (SCH-SQW) and up to T=612 K (SCH-MQ). The laser pulse energy at T=300 K was about 5 nJ. The far field pattern consisted of an oval spot with the divergence (θ/2)‖ = 14° in the sample plane and (θ/2)⊥=26° in the perpendicular plane. Fig. 1 shows the laser threshold as a function of temperature and the emission spectra near the threshold at T=500 K (inset). It was shown, using photoluminescence measurements, that the SCHs are stable up to T=500 K. Heating the samples at T=500-650 K leads to a slow (without the N2 laser beam) or to a fast (with the N2 laser beam, Iexc> 100 kW/ cm2) degradation. It has been found experimentally that irradiation of the structures with the N2 laser beam (50-150 kW/cm2) in a temperature range of 400 500 K improves the structure properties and results in a significant increase of the stimulated emission output (Fig. 2) and in a laser threshold reduction.
Frequency quadrupled passively Q-switched miniature Nd:YAG ring laser with 110 mW average power at 266 nm in single-frequency operation
Authors: Bode M. , Spiekermann S. , Tunnermann A. , Alvensleben F. v. , Welling H. , Freitag I.
Published: February 2023

Pulsed sources of ultraviolet radiation are attractive for a growing number of applications, ranging from trace gas monitoring with extremely high sensitivity to micromachining of highly integrated electronic devices. The pulse to pulse stability of laser parameters like output energy, peak power and pulse width required by these applications is ideally fulfilled by laser sources emitting on a single optical frequency. This can be achieved by subsequent frequency doubling and quadrupling of diode pumped solid state lasers with high stability.
Distributed Feedback Laser on Jelly-Like Dye Doped Gelatine
Authors: Efendiev T.Sh. , Katarkevich V.M. , Rubinov A. V. , Ryzhechkin S.A.
Published: February 2023

It is known, that the dichromated gelatine is suitable and often used for optical recording the holographic gratings. Here we propose for the first time to employ for this purpose the dye doped jelly-like gelatine without activation by dichromate of ammonium and without any subsequent chemical processing. Such medium allows to record stationary 3-dimentional gratings with high spatial resolution which provides efficient steady-state distributed feedback (DFB) in a dye laser.
On electrodynamic effects determining ultimate pump intensities for microsphere and microdisk resonators
Authors: Gruzdev Vitali E. , Libenson Mikhail N.
Published: February 2023

High quality factor of microsphere (MS) and microdisk (MD) resonators results in many their outstanding properties. On the other hand, such high-Q resonators can confine large electromagnetic field in small volumes. In this connection problem of radiation-induced damage of MS and MD resonators becomes important because optical damage limits both output radiation power (intensity and energy) and intensity of optical pumping Problem of laser-induced damage of microresonators should be mainly connected with their resonant properties rather than influence of absorbing inclusions and requires specific theoretical consideration
Spatio-Temporal Dynamics of Topological Events on Laser Wavefronts
Authors: Soskin M. S. , Vasnetsov M. V. , Kreminskaya L. V.
Published: February 2023

Wavefront dislocations are important topological features of propagating laser beams [1]. We report a scenario of spatio-temporal dynamics of birth, transformations and annihilation of screw dislocations (optical vortices) accompanied with phase saddles and extrema. These topological objects appear on a wave front when initially regular Gaussian beam is corrupted via self-action in a nonlinear medium. A topological map of the phase objects on the wave front is calculated, and the fundamental principles of topological transformations, or topological events are analysed. In the calculations we approximated the lens as Gaussian focusing or defocusing lens. A stigmatic Gaussian lens produces rings of zero field amplitude at certain distances. Even a small amount of astigmatism makes the closed lines of zero amplitude be stretched along the direction of the beam propagation, and in the beam cross-section four points of zero amplitude appear (“quadrupole” of optical vortices). Figure 1 shows the shape of a wave front within one quadrant and the topological objects on it. The total number of phase saddles equal 6, with associated index -6. There are also 4 maxima and 3 phase minima, including the central one, with the total index +7, what makes the whole wave-front topological index equal +1. In all other transformations, including vortices birth and annihilation, this index is constant, corresponding to the value of the initial smooth wave front index +1. This study can be used in the analysis of laser beams generation in optical cavities with phase-conjugated mirrors and propagation in free space and nonlinear media.
Computer-Generated Holograms for Beam-Shaping: Design Methods and Experimental Results
Authors: Beyerlein M. , Dresel T. , Schwider J.
Published: February 2023

The flexibility of computer-generated holograms (CGHs) permits to change an incoming wavefront in an almost arbitrary manner. For the design of CGHs for beam-shaping different parameters can be taken into accout. We use a geometrical optics approach to calculate elementary hologram functions which reconstruct simple intensity distributions. An object-oriented hologram design can be performed by combining the elementary focal patterns. The simulated reconstructions from phase-only hologram functions agree very well with the optical reconstructions.
High-Power Tapered Semiconductor Amplifier with Nd:YAG Microcrystal Master Laser Oscillator
Authors: Jost G. , Martin U. , Jäger R. , Heerlein J. , Unger P. , Schmitt N. P. , Königer M.
Published: February 2023

We report on a novel system consisting of a tapered semiconductor laser amplifier driven by a diode-pumped microcrystal Nd:YAG master laser oscillator. With this kind of system it is possible to combine the excellent spatial and spectral beam quality of a microcrystal solid-state laser and the high electrical to optical power conversion efficiency of a semiconductor amplifier. The system has the capability of hybride integration and has a theoretical wall-plug efficiency of more than 25%.
Output Beam Quality Improvement using a Narrow Input for Tapered Semiconductor Laser amplifiers
Authors: Lin Ching-Fuh , Lai Jie-Wei , Chang Yu-Chia
Published: February 2023

Coherent high-power semiconductor lasers are important for many applications due to their compactness, low-cost, and possible integration with other photonic devices. Several types of semiconductor laser amplifiers have been proposed to increase the output power. Among them, the tapered semiconductor laser amplifier has demonstrated the highest output power and still has a good beam quality [1]. However, filamentation is still formed when the device is operated at a much higher power level. In the tapered amplifier, the linearly tailored gain region serves as the spherical expansion of the wave front. The expansion is not ideal because it does not start from a point source, which unfortunately does not practically exist. We propose that the input aperture with its size close to the wavelength could work like a point source and so significantly improves the output beam quality.
InAsSbP/InAs LEDs FOR THE 3.3-S.3 μm SPECTRAL RANGE
Authors: Matveev B. , Zotova N. , Karandashov S. , Remennyi M. , Il’inskava N. , Stus' N. , Shustov V. , Talalakin G. , Malinen J.
Published: February 2023

The report presents data on narrow band (FWHM ≅ λmax/10) room temperature LEDs fabricated from InAsSbP/InAs heterostructures grown at Ioffe Institute and emitting in the 3.3-5.3 μm spectral range with emphasize on LEDs for methane (3.3 μm), carbon (4.3, 4.7 μm) and nitric (5.3 μm) oxides optical detection.
Mid-infrared picosecond optical parametric oscillator based on periodically-poled RbTiOAsO4
Authors: Kennedy G. T. , Reid D. T. , Miller A. , Ebrahimzadeh M. , Karlsson H. , Arvidsson G. , Laurell F.
Published: February 2023

Optical parametric oscillators (OPOs) pumped by the Kerr-lens-mode-locked (KLM) Ti:sapphire (TiS) laser are practical sources of picosecond pulses. Until recently, the operation of these devices was confined mainly to wavelengths below -3 pm. We have now extended the operation of these devices into the mid-infrared by exploiting the new quasiphase-matched (QPM) nonlinear material RbTiOAsO4 (PPRTA).
Femtosecond code-division multiple-access system with 1.3 μm Cr:forsterite laser
Authors: Takasago K. , Furusawa T. , Kanuari F.
Published: February 2023

There is increasing interest in utilizing optical code-division multiple-access (CDMA) schemes in fiber-optic local area networks because of its wide bandwidth, high information security, and the capability for multiple access. Both synchronous and asynchronous optical CDMA system have been actively studied. In general, the numbers of subscribers and the simultaneous users are larger in the synchronous CDMA although the system is more complex. However, a femtosecond CDMA scheme based on spectral encoding and decoding, which is categorized as an asynchronous scheme [1], can allow a large number of simultaneous users. [2] In this paper, we demonstrate the femtosecond code-division multiple-access based on spectral encoding of 1.3 μm Cr:forsterite laser.