bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser-tissue interactions studied by time-resolved stress detection
Authors: Oraevsky Alexander , Jacques Steven , Esenaliev Rinat , Tittel Frank
Published: February 2023

Acoustic transients induced by short laser pulses in biological tissues carry specific information about axial light and temperature-field distributions, absolute values of elastic and recoil pressure, and stress wave propagation (see Fig. 1). Time-resolved detection of laser-induced stress transients with a broad-band lithium niobate acoustic transducer allows absolute measurements of initial thermoelastic stress distributions in turbid and layered media. Optical properties of biological tissues can be determined from stress magnitudes and exponential slopes. Laser ablation causes a recoil momentum transfer upon material ejection. Measurements of recoil stress kinetics helps to clarify ablation mechanism and to determine optimal laser parameters for efficient laser ablation with minimal thermal and mechanical injury to adjacent tissue layers.
The design of high-power multistage KrF laser system "GARPUN"
Authors: Basov N. G. , Bakaev V. G. , Metreveli G. E. , Sychugov G. V. , Vadkovskii A. D. , Zvorykin V. D. , Lebedev P. N.
Published: February 2023

The e-beam-pumped KrF laser "GAR-PUN" produces 100 ns pulses with an output energy of ~100 J and peak power ~1 GW in free-running and injection-controlled narrow-band operation.1 In this paper we describe a design of a multistage KrF laser system with an expected output power of 5-10 GW in nanosecond range.
Fibre amplifiers and fibre lasers
Authors: Payne David N.
Published: February 2023

The erbium-doped fibre amplifier has effectively banished loss from the lexicon of the optical communications designer and has changed the course of telecommunications. Fibre lasers are beginning to have a similar impact, providing spectral coverage from 400 nm to beyond 3 μm, pulse widths of a few tens of fs and output powers up to 5W. Photorefractive fibre gratings have recently allowed the construction of DFB fibre lasers.
Optical parametric oscillators
Authors: Dunn Malcolm H.
Published: February 2023

Optical parametric oscillators (OPOs) use nonlinear optical effects to generate coherent radiation over extensive and continuous tuning ranges. In recent years the advent of new and improved optically nonlinear materials coupled with the development of increasingly refined lasers, in particular diode-laser-pumped solidstate lasers, as pump sources for OPOs has led to a resurgence of interest in these devices as practical sources of tunable, coherent radiation. High optical-to-optical conversion efficiencies have now been demonstrated in devices that operate from the femtosecond through the nanosecond and picosecond time domains to truly continuous-wave oscillation. Spectral control can be to the transform limit. Decade tuning ranges converting the near ultraviolet, visible, and near infrared are now possible from a single, compact device. This tutorial review talk will introduce the basic physical principles behind these devices, and will report on the current status of the rapidly evolving science and technology of OPOs throughout all of the above time domains.
Photoacoustic determination of optical parameters of biological tissue
Authors: Ruff Chr. , Lohmann S. , Lubatschowski H. , Ertmer W.
Published: February 2023

These studies are directed towards an on-line monitoring of tissue properties during medical laser applications for diagnostics and therapy. These properties are in particular the optical parameters (i.e.absorption and scattering) and in the case of invasive treatments such as photoablation the depth of the incision.
Growth and characterization of the Cr4+ doped crystal fibers
Authors: Nikolaev D.A. , Rusanov S. Ya. , Shcherbakov I.A. , Tsvetkov V.B. , Yakovlev A.A. , Fiebig M. , Tuennermann A. , Welling H.
Published: February 2023

In the last time Cr4+-doped crystals have been applied to create tunable solid-state lasers near the 1.5 μm spectral range, which were pumped by the emission of the Nd-lasers. Of particular interest are Cr4+-lasers which are laser diode pumped, but this problem has not been solved up to now. We suppose that the best way to achieve this goal is to use Cr4+ doped crystal fibers as the active elements of the lasers. In this case the pumping area is limited by the fiber and the volume is small enough to achieve the necessary power density of the pumping.
Quantum Engineering of Optical Nonlinearities in Semiconductor Heterostructures
Authors: Rosencher Emmanuel
Published: February 2023

Cubic semiconductors are ideal materials for nonlinear optics because i) their second order optical nonlinear (SOON) coefficient is huge (typically 100 pm/V in GaAs), ii) their damage threshold is extremely high (few GW/cm2) and iii) a great deal of technological knowledge has been gained during the past decades due to their large industrial importance. However these semiconductors have never reached a mature status in nonlinear optics, the main reason being that those materials are naturally not biréfringent and consequently cannot be phase matched. This situation has changed drastically in the last few years.
A pulse stabilised micro-chip laser
Authors: Arvidsson Magnus , Hansson Björn , Laurell Fredrik , Lindström Carsten , Olsson Magnus
Published: February 2023

Diode pumped solid-state laser is a rapidly growing field. Passively Q-switched micro-chip lasers are particularly interesting as they can give short pulses (<ns) with high peak power (kW) for moderate diode pump powers in an extremely simple configuration. A disadvantage, however, is that the passively Q-switched laser has a considerable pulse repetition frequency jitter accompanied by pulse to pulse amplitude fluctuation [1].
High Power Diode-Pumped Solid-State Lasers
Authors: Tünnermann A.
Published: February 2023

Solid-state lasers operating at high continuous wave output power are attractive sources for various applications in materials processing and nonlinear frequency conversion. Since the development of reliable high power diode arrays, numerous publications have reported on the superiority of these pump sources compared to the conventional excitation with flash lamps [1-5]. While first generations of solid-state lasers were directly pumped with diode lasers, the application of fiber-coupled diodes has been prooven to result in significant improvements of system parameters, such as reliability and stability [2, 5].
Design and performance of a compact 600W cw Nd:YAG rod laser system pumped by microchannel-cooled stacked diode laser arrays
Authors: Brand T. , Schmidt I.
Published: February 2023

A diode pumped solid-state laser with an average output power of several hundred watt as needed for many material processing applications suffers from the high cost introduced by the laser diode modules. One possibility to decrease the cost of the pump modules is to reduce the demands for the spectral and output power characteristics of the individual bars within a stacked array which may result in an improved yield for the diode manufacturer. Further, the laser designer should avoid to introduce additional complexity like precisely aligned and coated coupling optics or fiber coupling of the laser diodes as far as possible.
All solid-state diode pumped Nd:Yag MOPA with stimulated Brillouin phase conjugate mirror
Authors: Offerhaus H.L. , Godfried H.P.
Published: February 2023

At the Nederlands Centrum voor Laser Research (NCLR) a 1kHz diode-pumped Nd:YAG Master Oscillator Power Amplifier (MOPA) chain with a Stimulated Brillouin Scattering (SILS) Phase Conjugate mirror has been designed and operated. A small Nd:YAG zig zag slab (1.8 by 1.7 by 40mm) is side pumped with 200μs diode pulses in a stable unidirectional ring oscillator. The oscillator is Q switched and injection seeded with a coin menial diode pumped single frequency CW Nd:YAG laser. The output consists of 25μs FWHM-pulses at 1064mm in a single-transverse, single-longitudinal mode. The oscillator slab is imaged on a square aperture that transmits about 80% of the energy. The aperture is subsequently imaged four times in the amplifier. The amplifier is a 3 by 6 by 60mm Brewster angle zig-zag slab, pumped by an 80-bar diode stack with pulses up to 250μs. After the second pass the light is focused in two consecutive cells containing freon-113 for wave-front reversal in an oscillator/amplifier-setup with a reflectivity of 60%. The light then passes through the amplifier twice more to produce 40W output with near diffraction limited beam quality. The zig-zag slab in the oscillator effectively reduces thermal lensing effects and the Brillouin scattering reverses any alterations originating from the amplifier.
Multiwave Interaction and Nonlinear Holographic Recording in Bi12TiO20
Authors: Petrov M.P. , Petrov V.M. , Zouboulis I. , Xu L.P.
Published: February 2023

Investigations of two- and four-wave mixing in photorefractive materials are well known. However, these studies have mostly been carried out in volume holograms where diffraction phenomena are observed under Bragg conditions which impose strict limitations on possible combinations of interacting beams and, as a result, only interaction between the zero order of one beam and the first diffraction order of another beam is considered in most cases. This report discusses the studies of wave mixing in thin holograms where there are no Bragg limitations. In the experiments, thin plates of Bi12TiO20 and the adaptive interferometric technique involving phase modulation of one of incident beams were used. It was shown that not only two-wave, but also induced three-wave and even multiwave mixing can be detected in thin holograms in case of nonlinear holographic recording in spite of the fact that only two incident beams record the hologram. This occurs because different combinations of diffracted beams from various spatial, harmonics of an initial sinusoidal grating can propagate in the same direction and efficiently interfere with each other. As many as seven diffracted orders were observed. Thorough investigations of polarization have shown that they are associated with seven spatial harmonics of the recorded grating. Theoretical analysis of the observed phenomena has been performed.
Light Scattering by Microdomains in Photorefractive Lithium Niobate Crystals
Authors: Obukhovsky V.V. , Lemeshko V.V.
Published: February 2023

Recently the hologram storage in photorefractive crystals due to domain grating formation under light influence [1-3] was discovered. In some crystals (for example, in SBN-75 [3]) these gratings are connected with modulated array of microdomains. As a result of microdomains parameters fluctuations a noise of holograms can arise.
Continuous-Wave Operation up to 36°C of GaInAsP/InP Strained-Layer Multi-Quantum-Wells Surface-Emitting Laser
Authors: Uchiyama S. , Yokouchi N. , Ninomiya T.
Published: February 2023

A 1.3-μm GaInAsP/InP surface emitting (SE) laser has wide application in optical communication and optical inter-connections. Previously, we improved a buried heterostructure for GaInAsP/InP SE laser regrown by metalorganic chemical vapor deposition (MOCVD)[1] and introduced Si/Al2O3 layer, which has a higher thermal conductivity than Si/SiO2 layer, into p-side mirror of 1.3-μm SE laser 12] and demonstrated 1.3-μm SE lasers with a bulk active layer. A low threshold room-temperature pulsed operation (Ith= 12mA) and a continuous-wave (CW) operation up to 13 °C were obtained[2]. Recently, the room-temperature CW operation of 1.5-μm SE laser with strained-layer multi-quantum-wells (SL-MQW) was reported [3]. To get better performances of a 1.3-μm SE laser, it is considered to be important to introduce a SL-MQW into its active layer. In this study, we have demonstrated a 1.3-μm GaInAsP/InP SL-MQW SE laser and have achieved CW operation up to 36°C, which is the highest CW operating temperature for long-wavelength SE laser.
The data-address separation for all optical ATM
Authors: Park Ki Hwan , Mizumoto Tetsuya , Matsuura Akihiko , Naito Yoshiyuki
Published: February 2023

The all optical ATM is an attractive transmission method of information that realizes B-ISDN in the future. The speed of information signal processing in all optical scheme is higher compared with the electrical control. In order to realize the all optical ATM,it is required to establish the method for recognizing address in an all-optical manner.
Intracavity Sub-G Hz-Mod illation of Nanosecond Laser Pulses via Resonator enhanced Four Wave Mixing
Authors: Kramer M.
Published: February 2023

The temporal shape of laser pulses emitted from an unstable laser resonator was investigated [1, 2]. The resonator was Q-switched by means of stimulated Brillouin scattering (SBS) in a cell filled with acetone. Besides a change in pulse length from 40 ns to 2-3 ns by a variation of the resonator configuration, sub-GHz-modulations of the 40 ns-pulses were observed (fig. 1a)-c)). In a set of 150 laser shots 28 were strongly modulated, which were taken for analysis in fig.2. Only modulation frequencies which are harmonic multiples of the resonator roundtrip frequency (100 MHz) appeared whereas frequencies of 400 MHz and above 600 MHz were missing. It is remarkable, that the measured frequencies belong to a subharmonic of the Brillouin shift (in acetone 3000 MHz at 1064 nm), whereas the missing frequencies are no subhamtonics of the Brillouin shift. It turns out, that the modulations are caused by a not too low Q-value before the Q-switching of the laser, which enables prelasing. Based on long prelasing pulses a spontaneaous mode locking takes place, which is responsible for the statistical behavior of the modulation frequencies. If the modulation frequency of this mode locking is matched to the Brillouin shift, a four wave mixing process is initiated in the SBS-cell causing a Q-switch of the resonator. In analogy to Brillouin enhanced four wave mixing (BEFWM) this process may be called resonator enhanced four wave mixing (REFWM).
CW Operation of Selectively Oxidized Vertical-Cavity Surface-Emitting Lasers from -80°C to 130°C
Authors: Weigl B. , Grabherr M. , Reiner G. , Ebeling K J.
Published: February 2023

The use of selectively oxidized layers as current aperture for vertical-cavity surface-emitting lasers (VCSELs) has drastically improved device performance[1]. We report on high wallplug efficiency (32%). high output power (16mW), and wide temperature (-80°C to 120°C) cw operation of oxidized VCSELs.
Sub-Wavelength Microscopy
Authors: Tychinsky Vladimir
Published: February 2023

The experimental results with Contrast Enhancement and Phase Microscopes have proved the possibility of ten-fold increasing resolution over classical limit, which is based on coherent transfer function. The previous results on computer modelling, theoretical and experimental investigations are discussed. We propose the approach which permits to explain these results and to avoid the contradiction with Abbe's theory. In our approach we use an optical system eigenfunctions instead of plane waves as a basis for the object field decomposition and consider the microscope lens and reflecting object as a fragment of an equivalent lens waveguide (or a resonator) with known set of eigenfunctions.
Analysis of optical pattern formation by symmetry autocorrelation functions
Authors: Neubeckcr R. , Tschudi T.
Published: February 2023

Today, spontaneous pattern formation is a phenomenon observed in a wide spectrum of nonlinear optical systems [1,2]. Still, the systematic analysis of such patterns is a problem, because of the lack of general characterization algorithms, allowing a quantitative evaluation of the patterns’s complexity.
Stimulated Brillouin Scattering Phase-Locked Phase Conjugation
Authors: Scott A.M. , Ridley K.D. , Soan P.
Published: February 2023

A new loop geometry was recently investigated for SBS phase conjugation and was shown to greatly improve the stability of the phase conjugation process by eliminating phase jumps which can degrade the stability and fidelity [1]. The loop increases the coherence length of the laser output [2], making it suitable for heterodyne laser radar.
Tunable side-on diode-pumped Yb:fluoride phosphate glass laser with high efficiency
Authors: Griebner U. , Koch R. , Schönnagel H , Ehrt D. , Seeber W.
Published: February 2023

Yb:YAG and several other Yb-doped crystals have been demonstrated to lase efficiently [1]. Recently, Yb3+ in glass host materials have also attracted much attention especially because of the smaller reabsorption at the laser wavelength and the much smoother spectra compared to Yb:YAG. The used Yb:fluoride phosphate glass was developed at the University of Jena. An interesting feature of this glass is the higher absorption cross section at 973 nm (σa = 1.2 × 10−20 cm2). The Yb:fluoride phosphate glass was doped with 5 × 1020 cm−3 Yb3+ and exhibits a fluorescence lifetime of 1.2 ms Laser performance of this glass has been impressively demonstrated with a slope efficiency of 55% and a maximum cw output power of 460 mW by longitudinal pumping with a Ti:sapphire laser [2].
Testing of distributed fiber optical strain sensors for long term surveillance of a stay cable bridge
Authors: Brönnimann R. , Nellen Ph. M. , Sennhauser U.
Published: February 2023

Monitoring mechanical strength and integrity of critical civil structures are of great importance for their safety. Mechanical properties of materials and structures are tested and surveyed by measuring strain and deformation under static and dynamic load. Many fiber optical detection concepts have been proposed and investigated [1,2]. But the industrial acceptance of fiber optical sensors will be low unless performance and reliability of optical sensors are demonstrated.
Hydrogel based distributed fibre optic sensor for measuring moisture content in soils
Authors: Hadjiloucas S , Keating D A , Usher M J , Michie W C , Culshaw B , McLean A
Published: February 2023

Fibre-coating techniques with hydrogels (hydrophilic polymers) in conjunction with optical time domain reflectometry, offer the possibility of producing a distributed chemical sensor for detecting the presence of water (Michie et al., 1995). In tins paper, we extend the range of possible applications of such hydrogel based sensor, to measure water content of soils. The sensor is based on measurements of the changes in the Rayleigh backscattering signal induced by quasi-sinusoidal distortions of fixed periodicity on a multimode graded index optical fibre. In the presence of water molecules, the swelling action of a poly (ethylene oxide) based hydrogel coating, which is deposited on a GFRP support cable, causes the fibre to deform locally by squeezing it against a kevlar thread, helically wound along the length of die sensor cable (Fig. 1). The resonant period for die microbend is equal to the pitch length of the kevlar thread and is given from Δ
m
=2πr/(2δ)
–1/2
where r is die core radius and δ is the maximum refractive index difference between die core and cladding, forcing die system to operate at a resonant mode.
Investigation into the Influence of Interaction Time In Laser Cladding Process
Authors: Kathuria OY P , Tsuboi Akihlko
Published: February 2023

As with the conventional cladding process e.g. TIG, oxyactylene and plasma arc surface welding, where the interaction time is much longer and it results in superheat generation, which further Induces the post melting and also vigorous mixing of the pool, thus producing good interfacial bonding but more dilution, large H A Z and less hardness etc.. Whereas with the laser cladding process, the superheat generation could effectively be controlled over the length of the interaction time thus producing less dilution, small H A Z and higher hardness value etc.. In this process a molten pool of the pasted or blown powder with a complex three dimension al (3D) shape is formed on the substrate, by the laser beam interaction with powder material. This interaction time plays a crucial role for the desired successful cladding. In our present analysis we find that in a narrow range of power density and beam interaction time, the regime of laser cladding could further be classified (Fig.l) for evolution of coarse(C), fine(B) and very fine(A) dendrite microstructures. The experimental results which were performed with stellite #6 on Cr-Ni and mild steel using a 5KW CO2-laser in the stationary and oscillating beam mode, show that for longer interaction time there is a post melting due to the superheat of the molten pool and also the flow within the molten pool is vigorous, resulting In a better mixing, thus lowering the average temperature gradient of the interface which varies as the bulk temperature.
Analysis of the Effect of Optically Induced Local Non-Uniformities in Laser Surface Treatment Applications
Authors: Ocaña J.L. , García-Beltrán A. , Lupón N. , Laguarta F. , Armengol J. , Vega F.
Published: February 2023

The smoothing of laser beam intensity spatial distributions is a practical need for the development of a majority of laser surface treatment applications. However, the current use of homogenizing waveguides such as kaleidoscopes is not generally a satisfactory solution because of their relatively high associated laser energy loss.
Laser based diagnostics in art conservation
Authors: Fotakis C. , Anglos D. , Balas C. , Couris S. , Zafiropulos V.
Published: February 2023

The degree of success of any art conservation technique relies on the availability of non destructive diagnostic techniques, which apart from providing information about the state of preservation and composition of artworks can be used for on line process control, safeguarding against potential damage. Laser based analytical techniques have been used for obtaining in situ information about the chemical composition of art objects in this respect. In addition, modem imaging techniques have been used for documenting macroscopic color and structural information [1].
The Appearance of Tilted Waves, Sources and Sinks in Simple Mode-Locked Laser Patterns
Authors: Slekys G. , Staliunas K. , Lovergneaux E.
Published: February 2023

It is known that the transverse modes under certain conditions lock to a common frequency We investigated the locking processes more in detail, focussing on the analysis of the phase relations between the locked modes.
Slab waveguide CO2 laser with double Talbot filtration
Authors: Abramski K.M , Plinski E F. , Duda P.A. , Witkowski J S , Borkowicz Z.
Published: February 2023

Slab-waveguide molecular CO2 lasers with transverse RF discharge excitation are attracting attention through their compatibility with diffusion cooling and capability for high average power under scaled off conditions [1]. The slab waveguide resonator modes can be adequately described by simple rectangular EHml modes when the lateral Fresnel number of the cavity considerably exceeds unity. Very poor beam quality of the laser output (parameter M2 > 20) is the multimode mixture of a few different lateral modes with lateral index m of the resonator inserted between 1 and 50 [2]. Effective single-mode operation of a such laser can be obtained by so called Talbot selection of a lateral waveguide mode of the laser resonator [3]. It was accomplished via the insertion of a grid mode selector into the laser cavity to promote oscillation in a single high order waveguide mode. The spacing d of the grid wires is chosen to fulfil the Talbot imaging condition within the given rectangular waveguide structure according to Talbot condition L = (nd2/2λ), where L. is the cavity length, d is the wire spacing, λ is the wavelength, n is a small integer that represents the number of imaging planes on each round trip through the laser cavity. It was shown that the Talbot selection reduces output power to about 60-70% relative to multimode operation.
Transparent low-loss N × N optoelectronic switch fabric
Authors: Collings N. , Herzig H.P. , Müller M.
Published: February 2023

There is considerable interest worldwide in reconfigurable, transparent switch fabrics with low loss for both telecom and computing applications. A number of architectures employing liquid crystal devices have been suggested for switches where reconfiguration times of µsec to 1 sec are acceptable [1]. These-are either multistage, with control and latency overheads, or single stage, such as the matrix-vector multiplier approach with 1/N2 loss (N being the number on input and output channels). An alternative single stage scheme, where a computer generated hologram is written on the SLM [2,3], charges the latter with the task of control and beam shaping. The use of multi-focus diffractive optical elements to direct the beam, which would relieve the charge on the LCTV and improve the throughput efficiency, has been proposed recently [4]. However, the results on the basic system show low throughput efficiency and unacceptable crosstalk, A high throughput efficiency is required for an acceptable bit error rate on a high speed link. The principle of a low-loss link based on free space optics is described in this paper.
Wafer-Fused Vertical-Cavity Bistable Device at 1.55 µm Wavelength
Authors: Jeannès F. , Lugagne-Delpon E. , Oudar J. L.
Published: February 2023

All-optical switching devices can simplify optical networks by allowing optically-controlled routing of signals. In this context vertical cavity (VC) devices are very attractive, for their insensitivity to beam polarization and easy coupling to optical fibers. At 1.55 µm wavelength, however, it is difficult to grow high reflectivity epitaxial mirrors lattice-matched to InP. For VC surface emitting lasers, a new approach, based on wafer-fusion, has been very successful to overcome this difficulty1. In this technique, an InGaAsP structure, lattice-matched to InP is bonded to an AlAs/GaAs Bragg mirror, matched to GaAs. Here we present a wafer-fused VC bistable device at 1.55 µm. It is an all-optical device, with no electrode, based on the carrier-induced nonlinear refractive index of an InGaAsP epitaxial layer.
Non-biased all-optical bistable device having a p-i-n-i-p diode within asymmetric Fabry-Perot cavity structures
Authors: Kwon O. K. , Kim K. , Hyun K. S. , Baek J. H. , Lee B. , Lee E.-H.
Published: February 2023

Recently, devices which show non-biased optical bistability (NOB) have been proposed with practical advantages such as low switching energy, low power dissipation, and very simple layout.1-2 For NOB operation, negative differential resistance (NDR) and the photocurrent (Iph) peak at forward bias region are essential. For the optimization of the NOB device performance, both of large electric field change and sufficient absorption change should be achieved under the only source of the potential, the built-in potential (V
bt
) due to the p-i-n diode structure.2 In this work, to induce strong light-absorption and internal field swing, we propose and demonstrate a novel NOB device, a series connection of two extremely shallow quantum wells (ESQWs) p-i-n-i-p diodes sandwiched in asymmetric Fabry-Perot (AFP) cavity structure.
Improved Hardness Characteristic of CO2 Laser Welded High Carbon Steels
Authors: Ng Eng S. , Watson Ian A , Abdullah Hussein A , Chatwin Chris R
Published: February 2023

Due to the low integrated energy input, laser welds are often quenched too rapidly in the fusion region [1]; this results in an untempered martensitic structure in samples with sufficient alloy content to retard formation of ferrite, pearlite and bainite. The high cooling rate of laser welding leads to a variation in the transverse hardness profile; and consequently, a very brittle weld [2,3]. To alleviate these poor mechanical characteristics, this work investigated pre-heating and post-heating of the sample to control the rate of cooling and prevent rapid quenching. Both approaches resulted in considerable improvement in the hardness profiles. Gauge plate (2mm thick) with 0.85% and 0.5% carbon content was welded, sectioned, photographed, and the microstructure was examined. The effect of varying the workpiece translation speed, i.e the degree of post heating and pre-heating, was quantified by measuring the sample’s hardness transverse to the weld direction. The present study used a 1kW CO2 laser (Ferranti MFKP) and a multi-pass scanning technique to control the sample’s phase transition and to achieve the desired weld characteristics. To control the rate of heating or cooling the workpiece was heated several times with 0.5 kW of unfocussed power. For the pre-heated geometry, 10 passes of the laser were used to heat up the base metal; this was followed by an additional pass to weld the sample with 1 kW laser power. Post-heating was achieved by welding the sample and then making 10 passes of the laser beam over the weld region.
Jitter suppression in a 2700km soliton propagation experiment using only a fibre Bragg grating filter
Authors: Harper P. , Knox F. M. , Kean P. N. , Zhang L. , Doran N. J. , Bennion I.
Published: February 2023

It is well known that the build up of Gordon-Haus timing jitter induced by repeated amplification along a soliton fibre link can be significantly reduced by the inclusion of fixed frequency filters in the system [1]. Here we present the first experimental results which show that it is possible to use fibre Bragg gratings as the only filters in such a system and that they compare favourably with bulk devices in terms of jitter reduction. The advantages of these devices are that they are fibre based, have low polarisation dependent loss and low insertion loss. In addition, the post-fabrication exposure technique [2] makes it easy to produce high finesse fibre filters whose pass-band characteristics can be chosen arbitrarily making them compatible with sliding frequency configurations. Fabry-Perot and multiple pass-band devices can also be written in a single fibre making them compatible with WDM systems[3].
Holographic Axicons as Diffractive Optical Elements for Real Space Image Formation
Authors: Popov S.Yu. , Friberg A T.
Published: February 2023

Since their first implementation into optics by McLeod in 1954 [1], axicons and their generalizations [2,3] have been a subject of continual interest and research. Due to their unique properties to form light distributions with substantially elongated focal depth, axicons allow in practice to overcome the Rayleigh-Abbe condition, which prevents producing deeply focused beams with high transverse resolution. The recent developments and achievements in the field of diffractive and micro-optics reveal new possibilities for axicon applications in the form of flat computer simulated holograms. This broadens the potential usage of the basic axicon principle to real space image formation.
UV-induced DFB Laser in Ge-free Erbium Doped Fiber
Authors: Sejka Milan , Hübner Jörg , Vanning Poul , Feuchter Thomas , Pálsdóttir Bera , Laisen C. Christian , Kristensen Martin
Published: February 2023

Recently, directly UV-written erbium DFB fiber lasers were produced [1,2] and shown to be excellent signal sources for telecommunication [3]. One of their attractive properties compared to semiconductor DFB lasers is the narrow homogeneous linewidth of the gam spectrum leading to reduced crosstalk and allowing cascading of several lasers [3]. Broadening of the gain spectrum and the quantum efficiency of erbium are closely related to the codopants in the fiber core. However, for UV writing certain codopants such as germanium are assumed necessary. More investigations are therefore needed to find optimum combinations of codopants that improve the behavior of the erbium doped fiber without disabling the UV-writing.
Interwell Carrier Transport In InGaAsP/InP Quantum Well Laser Structures
Authors: Marcinkevičius S , Fröjdh K. , Olin U , Silfvenius C , Stålnacke B , Landgren G
Published: February 2023

Carrier transport between quantum wells (QW) is assumed to be the slowest process involved in carrier transfer and redistribution in multiple QW InGaAsP/InP laser structures. Calculations show that effective hole trapping and slow thermionic emission cause nonuniform hole distribution in the active region [1] and increased gain compression [2], significantly affecting the high-speed performance of a laser.
Reduction of nonradiative current by sulphur passivation of InGaAs/AlGaAs laser diode facets
Authors: Sebastian J. , Beister G. , Daga O. P. , Gutsche D. , Erbert G. , Maege J. , Ressei P. , Weixelbaum L. , Weyers M.
Published: February 2023

For InGaAs/AlGaAs laser diodes catastrophic optical damage (COD) is the main factor limiting the output power. We have developed both an effective passivation method for such laser diodes on the basis of wet chemical sulphur treatment, and a non-destructive method to study the associated changes in the nonradiative surface recombination at the facets. This method is based on an analysis of power-voltage-current characteristics (P-V-I) in the low injection regime.
Theoretical Model of a Zeeman Gas Laser Operating Far from Threshold
Authors: Barmasova A.M. , Sokolov V.A.
Published: February 2023

Nonlinear interactions of two circularly polarized counterpropagating waves in the two-isotope gas active medium placed in an axial magnetic field are investigated on the basis of semiclassical theory. The polarization of the Doppler-broadened active medium is calculated without use of the perturbation theory expansion over the intensity of laser field (that is in the case of the large gain parameter). Difference in relaxation constants of all possible polarization moments is taken into consideration.
Two-dimensional optical star-network
Authors: Danzer U. , Schwider J.
Published: February 2023

An interconnection network for a modular expandable multiprocessor system is shown. Such a computer system needs a direct coupling among all processor units. For synchronisation purposes or clock distribution the signal delay from one transmitter to all receivers should be the same. A fibre optical star network ensures a data distribution from all emitters to all receivers without delay, assuming equal fibre lengths.
Experimental Study of a Q-Switched Transverse-Diode-Pumped Neodymium Yttrium Aluminum Garnet Laser
Authors: Le Nevé M. , Jolly A. , Vial J. C. , Coïc H , Féru P. , Maruenda P. , Vicrcy J.
Published: February 2023

We present experimental results obtained with a Pockels cell or passively Q-switched transvcrsc-diode-pumped Nd : YAG laser The pumping head is made of 36 QCW diode bars from Mc Donnell Douglas Corp. (4500 scries), which are closely coupled onto the Y AG rod (Crismatec). The active length and diameter of the cylindrical rod equal 10 and 6 mm. respectively. The total diodes energy is 800 mJ. when the pumping duration Tp and drive current Ip equal 400 µs and 65 A. We don't use any temperature control and the frequency is kept below a few Hertz. The diodes emission wavelength is then above 805 nm, leading to a coupling efficiency. ηc, near 70 %.
Speckle - myographic Investigation of Biomechanical Characteristics of Muscular Contraction in Healthy Men and Patients with Muscular-tonic Syndromes of Lumbar Osteochondrosis
Authors: Vasilevskaya L. A. , Tanin L. V.
Published: February 2023

Lateral resonance low-frequency vibrations responsible for the temporal changes of the skin surface relief arise at the muscular contraction. On exposure of the skin area over the contractional muscle to coherent radiation, the change of the speckle field intensity fluctuations occurs. The dynamics of this process is dictated by the dynamics of the object under study. So, making investigations on the spectral properties of the reflected scattered laser radiation, we can judge about the character of changing the skin surface itself.
Numerical Simulation of Infrared-Photoablation
Authors: Franke H.-G. , Olmes A. , Bänsch E. , Lubatschowski H. , Dziuk G. , Ertmer W.
Published: February 2023

The ablation of soft tissue with pulsed IR-lasers is a thermal evaporation process. The influence of the temperature dependence of the optical absorption coefficient is not yet really understood [1,2]. Until now UV-photoablation of soft tissue has been supposed to be based upon photochemical mechanisms. Recent experimental results also allow a thermal interpretation [3].
High Power Pulsed Semiconductor Laser for Eyesafe Laser Range Finders
Authors: Andersson Lars , Renhorn Ingmar , Nilsson Stefan , Klinga Tiina
Published: February 2023

For laser range tinders utilizing the time-of-flight principle the maximum measurable distance is limited by the output power of the laser. The optimum wavelength with respect to eyesafe opearation is 1.5µm. For short pulses, 1-1000 ns, the maximum allowed pulsed power is in fact almost one million times higher compared to 0,9 µm wavelength! For this application the InP based semiconductor laser has a number of interesting properties such as small size, high efficiency and ability to lase at the desired wavelength.
Densely doped active waveguides
Authors: Jaskorzynska Bozena
Published: February 2023

Dielectric waveguides doped with rare-earth (RE) ions can be used as optically pumped amplifiers and lasers. In long (several meters) fiber devices, an outstanding example being the erbium-doped fiber amplifier, high gain (>30dB) can be accumulated along the device at low concentrations of RE ions. The length of integrated devices-[l] is restricted to a few centimeters and. therefore, two orders of magnitude higher RE concentration is required to provide sufficiently large gain. However, at high dopant levels strong interactions between RE ions tend to severely reduce gain efficiency Especially, cluster formation, which is difficult to eliminate, is harmful, since fast (nanosecond tune scale [2]) energy transfer between clustered ions may totally quench the gam lor realistic pump powers Understanding, and quantitative evaluation, of concentration dependent gain limiting mechanisms is of the fundamental importance for optimizing fabrication and design of densely doped active devices, in this talk progress in the ongoing research addressing this issue (2-8), as well as examples of demonstrated RE-doped integrated devices [9-12] and the design concepts for gain improvement [13-15), will be presented.
Frustrated Total Internal Reflection Q-switched Er:YAG and CrEr:YSGG Lasers
Authors: Högele A. , Ziolek C. , Lubatschowski H. , Ertmer W.
Published: February 2023

Q-switched Er:YAG and CrEr:YSGG lasers are of great interest for many applications in laser medicine and time resolved infrared spectroscopy due to the very high absorption of the 3 µm- radiation in water. The light modulators based on the effect of frustrated total internal reflection (FTIR) [1] appear to be very well suited for Q-switching of these lasers [2, 3, 4]. In this paper, the results of Q-switching of 2.94 µm Er:YAG, 2.79 pm and 2.70 µm CrEr:YSGG lasers with a specially developed FTIR modulator [4] will be presented. The wavelength of 2.70 pm is generated with a CrEr:YSGG laser in a dispersive resonator [4]. The energy output curves of single giant pulses are shown in Fig. 1. The correlations between the pulse energy and the pulse width for these wavelengths in the Q-switching regime have been investigated (Fig. 2). Ablation rates of corneal tissue at different fluences and histological evaluation of the laser induced thermal damage will also be presented and discussed. As a result, Q-switched erbium lasers seem to be a promising tool for many applications in laser surgery. This work is supported by the BMBF (german department for education, research, and technology) within the contract 13N6346/0.
Quantum Well Infrared Photodetector Arrays for Thermal Imaging Applications
Authors: Andersson J. Y. , Alverbro J. , Borglind J. , Helander P.
Published: February 2023

Long wavelength (8-10 µm) quantum well infrared photodetectors (QWIPs) based on intersubband transitions in n-doped AlGaAs/GaAs quantum wells (QW) are known to exhibit high detectivities D
*
= I 1010 -9-1010 cm Hz1/2 W1. Due to the well established GaAs material and processing technology QWIPs are viable candidates for high resolution (>128x128 pixels), low cost LWIR (8-12 µm) focal plane arrays (FPAs). Excellent wafer uniformities giving responsivity uniformities of 2-4 % across an array have been demonstrated and a temperature resolution NETD (noise equivalent temperature difference) = 20 mK is achieved . In the discussion below n-doped AlGaAs/GaAs QWIPs are assumed since, at least to date, these have been shown to provide the highest performance.
A traveling interference pattern photodetector for microwave signals
Authors: Merlet Th. , Dolfi D. , Huignard J-P.
Published: February 2023

We present a new photodetector based on the synchronous drift of photogenerated carriers with a moving interference pattern [1-3]. The proposed resonant photodetector is a semiconductor with injecting contacts, used as a high level heterodyne mixer. It detects the beating signal between two laser beams at different frequencies and provides a large detection volume which could be suitable for the efficient optical generation of microwave signals [4].
Microwave Waveguide Photodiodes with Distributed Absorption for High Power Applications
Authors: Jasmin Serge , Vodjdani Nakita
Published: February 2023

The wide developement of analog radio frequency (RF) optical fiber links for optically fed wireless communication systems and phased array antennas is partly conditioned by the availability of high speed, high efficiency photodetectors which can also deliver high RF power. Lumped or travelling-wave waveguide PIN photodetectors (WGPDs) [1,2] can achieve both high quantum efficiency and high bandwidth without any limitations in bandwidth efficiency product as in conventional PD. However in this WGPDs, carriers are generated in the first ten microns. As a consequence, under high illumination, the high photocarriers density in this small surface area, by space charge effects, modifies the internal electric field which in turn governs the carriers transport. This field screening induces non linearities of the electrical response of the PD for high optical power, and limits the maximum RF power which can be delivered. For higher power capabilities, diluted travelling-wave detectors (TWDs) have been proposed [3,4]. In order to further improve the power handling of the detectors and reduce the space charge effects, we propose and analyze a new microwave WGPD which distributes absorption over the maximum junction area available. The structure is based on a diluted singlemode WG with coupling and quantum efficiencies > 90% and can handle both high optical and electrical power. The photocarriers density is maintained constant along the whole propagation length of the diode (instead of being exponential) by controling and tailoring the modal absorption coefficient αΓ(z) along the axis of propagation (Fig.l). This design applies to lumped WGPDs as well as TWDs. For the distributed absorption WGPD presented here, the depleted region consists of a thin InGaAsP active layer sandwiched between transparent WG and contact layers and αΓ(z) can be varied by a factor of 10 by changing the WG ridge width from 2 to 4 µm. For a same junction area, the maximum RF output power can be 4 to 9 times higher for distributed absorption WGPDs as compared to diluted WGPDs [3,4] (lumped or TWDs). The structures are compared by using a drift-diffusion model which takes into account the heterointerfaces, device depolarization due to current flow in the load circuit and calculates the electric field in the depleted region in the linear regime (50 < E< 250kV/cm). At a given cut off frequency the figure of merit F is defined as the ratio of the maximum RF power to the incident optical power. F is optimized by choosing the maximum depleted region thickness (transit time limitation), the maximum junction area (RC time constant limitation for lumped detectors and 5 times more for TWDs) and by varying the reverse voltage and the optical power. Details of the design and performances of distributed absorption WGPD with coplanar transmission line will be presented in the conference.
Diffusely Scattered White Light Examination of Breast Tissue
Authors: Berg R. , Klinteberg C. af , Lindquist C. , Pifferi A. , Andersson-Engels S. , Svanberg S.
Published: February 2023

The optical properties of tissue are of interest in the development of new medical laser applications. Optical mammography, i.e. transillumination imaging of female breast to identify malignant lesions, is a diagnostic technique based on differences in the optical properties between tumours and normal healthy breast tissue. The wavelength region with the optimal properties for light penetration, spatial resolution and best diagnostic potential for this technique still has to be defined. In this investigation the absorption and reduced scattering coefficient for breast tissue has been measured in the wavelength range from 600 to 800 nm. These coefficients were derived by fitting the time-dispersion curve of the diffusely scattered light exiting the tissue, following illumination with short pulses, to analytical and numerical photon propagation models. By using femtosecond white light, the entire wavelength range could be covered simultaneously.
Contrast in Time of Flight, Near Infrared Laser Imaging Through Turbid Media
Authors: Joblin Tony
Published: February 2023

Ultrafast near infrared (NIR) lasers have been proposed as a tool for detection and diagnosis of breast disease. The advantage of using NIR photons is that they are non-ionising and hence provide a greater degree of patient safety than existing X-ray imaging methods. The investigation of NIR photon imaging techniques has also been pursued because NIR photons may be able to provide useful functional physiological and diagnostic information not present in X-ray images.
Optimising image processing systems to accurately count colony forming units
Authors: Ngiap Hio Chon , Watson Ian A , Wang Ruikang K , Ward Glenn
Published: February 2023

Historically, the rate of experimentation involving micro biological procedures is slow due to, for example, the incubation and analysis of samples. Recently, a number of optical and image processing techniques have been developed to analyse samples to improve accuracy by removing human error and speed up the data acquisition process. One such example where commercial products (Data Cell, Berks. U.K.) are available is in counting colony forming units (efu) grown on agar culture plates. Commercial products are prohibitively expensive and, in general, do not support other applications of the image processing equipment. The present work developed macros to count Escherichia coli using OPTIMAS, a commercially available software package for general image processing applications. The effect of the environment - lighting conditions, camera, focusing, threshold intensity, and filtering - on the efficiency of the counting system was investigated.
Low loss waveguides from inorganic-organic composites
Authors: Graf J. , Sautter H. , Zeitz B. , Krug H. , Schmidt H.
Published: February 2023

A new kind of optical material with a high potential for various high quality low cost devices has been optimized and applicated for optical waveguides. In order to meet the requirements of thermal and long-term stability inorganic and organic components were combined in an optical material consisting of a stable inorganic backbone and an additional organic modification with polymerizable organic groupings.