bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase Change Optical Recording Dynamics in the Picosecond Time Scale
Authors: Siegel J , Afonso C.N. , Solis J.
Published: February 2023

The feasibility of ultrashort laser pulse driven phase change optical recording has been recently demonstrated in GeSb thin films in which reversible write/erase (crystallization/amorphization) cycles have been performed with picosecond laser pulses [1]. Furthermore, it has been shown that the fluence threshold required for crystallizing a spot is considerably reduced for write pulses shorter than 1 ps, which has been interpreted in terms of electronic excitation effects [2]. However, the optimization of the material performances, including the determination and subsequent minimization of the transformation time, makes necessary to investigate the ps time scale transformation dynamics during the write/erase (w/e) events. This can be done by means of optical reflectivity measurements with ps-time resolution in a pump-and-probe scheme. The drawback of this approach is that the measurement would require the exposure of a fresh region of the recording media for each pair of pump and probe laser pulses since the pump pulse is aimed to modify the structure of the surface. Therefore several hundreds of write (erase) operations in different regions have to be performed in order to reconstruct the reflectivity evolution for a given fluence over a time window of just a few nanoseconds. Additionally, a laser system with an excellent pulse-to-pulse energy stability would be required since the w/e processes are critically dependent on changes of the irradiation pulse fluence. Streak cameras combine a high (ps-) time resolution with the feasibility of performing single pulse measurements, but their use has been reported very rarely for transient reflectivity measurements, and never in a real single-pulse configuration. This work reports on streak camera based, single-shot, optical reflectivity measurements with picosecond time resolution during ps laser w/e in Sb-rich films.
A Self Consistent Model for thr Kinetics of a HybriD Laser
Authors: Girard F. , Borgard J.M.
Published: February 2023

To improve CVL output power it has been shown that it is very interesting to reduce electronic density at the end of the post-discharge phase [1].

This attenuate the skin effect of the electromagnetic field and avoid an over-population of the lower laser levels before the lasing phase [2]. The HBr molecule can reduce the electronic density by dissociative attachment during the post-discharge [3].
A new design of four-pass dye laser amplifier and suppression of amplified spontaneous emission
Authors: Hahn Jae W. , Yoo Yong S.
Published: February 2023

Recently, Lee and Hahn1 demonstrated high energy efficiency of a four-pass amplifier by passing the laser beam back and forth four times on a single axis through a gain medium. This four-pass amplifier was capable to suppress self-oscillation to be generated by the laser beam traveling through the same pass in a high gain medium. However, the output beam of the four-pass amplifier involves quite big amplified spontaneous emission(ASE). They reported that the ASE portion reached to 15 % in normal operation. In the present work we introduce a new design of a four-pass amplifier suppressing the generation of ASE during the amplifying process, and describe the detailed operational characteristics of the new four-pass amplifier.
Optical and Temperature Distributions within High Power 980 nm Semiconductor Lasers
Authors: O’Brien Peter , McInerney John , Braddell Jules
Published: February 2023

Semiconductor lasers suffer from poor spatial coherence when operated at high powers. Deterioration in spatial coherence has been shown to be induced by carrier-induced self-focusing and temperature variations. Many device structures have been proposed to overcome this problem, including: phased arrays, unstable resonators, integrated-master oscillator power amplifiers and a-DFBs. Whichever solution is preferred, it would be of great benefit to observe the internal optical and temperature distributions under high power operation with a view to further improvement in device performance. In this paper we present an experimental technique which gives detailed information about the optical and thermal distributions within high power semiconductor lasers and show how this information can be used to improve performance of a curved facet unstable resonator.
Phase-locked array laser using a multi-mode interference coupler: theory and experiments
Authors: Camacho F. , Bryce A.C. , Marsh J.H.
Published: February 2023

A novel high power laser configuration based on phase-locked array resonators (fig. 1) is presented in this paper [1.2]. This configuration provides an efficient way of extracting high optical power from the lower power elements. Using quantum-well intermixing (QWI), we have monolithically integrated the four amplifiers/lasers with the passive multi-mode interference (MMI) coupler and output waveguide.
Electron and optical pulse shape measurement on a far-infrared free-electron laser using differential optical gating.
Authors: Gillespie W. A. , MacLeod A. M. , Yan X. , Knippels G. M. H. , van der Meer A. F. G. , Oepts D.
Published: February 2023

FELIX, the ‘Free Electron Laser for Infrared experiments’ was built by the Dutch foundation for fundamental research on matter, FOM, with the aim of providing the international scientific community with an intense, tuneable source of short pulses of radiation in the far infrared (5 μm - 100 μm). Work is currently in progress to extend the wavelength range to 300 μm. The FELIX user facility became operational in 1992 and now provides more than 3000 hours of beam time per year to users with applications in physics, chemistry, biology and medicine.
Repetition-Rate Multiplication in Actively Mode-Locked Fiber Lasers
Authors: Abedin Kazi Sanwar , Onodera Noriaki , Hyodo Masaharu
Published: February 2023

Active mode-locking has proved to be very effective in the generation of short, high repetition rate pulse train from fiber lasers. One of the limitation, however, is that the repetition rate of the pulses becomes limited by the frequency at which modulation is performed. It is, therefore, very challenging to find ways of increasing the repetition rate of the output pulses from an actively mode locked lasers without requiring any increase in the modulation frequency. Recently, Onodera et al. [1, 2] reported a novel scheme for several-fold multiplication in the repetition rate by applying rational detuning to the modulation frequency.
Investigations on Long Wavelength Quantum Cryptography Systems
Authors: Gibson F. , Hening A. , Bourennane M. , Jonsson P. , Tsegaye T. , Sundberg E. , Karlsson A.
Published: February 2023

Quantum cryptography is a technique for establishing a fundamentally secure key for cryptography using the encoding of the key on single photon states in such a way that an eavesdropper cannot acquire any information about the key without impairing detectable errors in the communication channel [1]. In the recent years there has been a remarkable progress in experimental implementations at 850 nm and 1300 nm wavelengths with secret key generation at kbits/s up to 48 km distance. However, for 1550 nm wavelength, where fiber losses are as smallest, progress has been hampered by the lack of good single photon detectors.
Quasi-Cycloidal Phase Profile Synthetic Aperture Technique for Passband-Broadened Arrayed-Waveguide Gratings
Authors: Parker M.C. , Farjady F. , Walker S.D.
Published: February 2023

Wavelength division multiplex (WDM) techniques are generally regarded as a key element in emerging broadband networks. Amongst the many passive device technologies being considered for wavelength selection, the arrayed-waveguide grating (AWG) [1] has multiplexing, demultiplexing and routing functionality. However, the non-rectangular passband characteristic of an AWG, due to die multiple convolution of input and output waveguide modes with the classical echelon transfer function of the waveguide array allows only a minimal wavelength-shift tolerance. In this paper we show how synthetic aperture techniques [2] can be employed to provide significant passband broadening and flattening. Figure 1 shows two possible geometries to achieve the desired phase control: either (I) profiling within the arrayed-waveguide, or (II) a geometric quasi-cycloidal deviation from the Rowland circle at the fan-out section.
Plasma kinetics issues during the excitation phase in an elemental copper vapour laser: influence of the “phantom current” on the formation of laser output.
Authors: Carman R.J. , Hogan G.P. , Webb C.E.
Published: February 2023

Experimental studies of the excitation phase in an elemental copper vapour laser immediately before the establishment of lasing action at 510.6nm and 578.2nm have shown that the discharge current can reach 60% of the peak value before any measurable excitation of the discharge plasma is observed [1]. This “phantom current” is observed typically 50-70ns before the appearance of spontaneous emission from Cu I states, and changes in atomic population densities in Cu I, as measured by spatially and time resolved hook spectroscopy. It has been proposed that the phantom current coincides with the acceleration phase of free-electrons remaining from the previous excitation pulse whose energies remain below the threshold for inelastic collisions [1]. However, a number of issues relating to the phenomenon remain unclear. For example, it is not known whether there is any significant energy deposition into the plasma during this period and whether this affects subsequent lasing action and overall efficiency of the laser. To provide further insight, a detailed computer model [2] has been used to simulate the plasma kinetics and lasing behaviour during the excitation phase of the discharge. The calculations have been carried out over multiple excitation/afterglow cycles to yield fully self-consistent results and accurately reproduce the pre-pulse plasma conditions. Results from the model will be compared with experimental data for I-V characteristics, radially and time resolved hook population densities for selected Cu I states, electron densities, and laser pulse intensities. Results from the model indicate that the phantom current can indeed be attributed to the acceleration and drift of the pre-pulse electrons which occurs as the electron temperature is raised to ~2-3eV corresponding to the threshold energies required for excitation of Cu states. The phantom current also coincides with a local minimum of the plasma resistivity which occurs as a result of the complex interplay between the electron temperature and the overall electron-heavy particle collision frequency. Under conditions where the phantom current is less important (ie. reduced pre­pulse electron density), the model suggests that laser pulse energies should increase, although this effect appears to be unrelated to power deposition issues during the period of the phantom current.
Carrier Diffusion and Gain Guiding effects in CD Laser Diodes
Authors: Evoy P. Me , Lynch S. , Landais P. , O’Gorman J. , Hegarty J. , Elsaβer W.
Published: February 2023

A self-pulsating laser diode emits a stream of short optical pulses at a well-defined repetition frequency. The self-pulsating emission has low coherence, which makes these lasers well suited for data storage applications since sensitivity to feedback is reduced. Shorter wavelength emitters are required for increased future compact disk storage. Development of these emitters requires greater understanding of self-pulsation in compact disk lasers, it’s causes, and the influence of laser structures and materials. We present an investigation into the effects of carrier diffusion and carrier density refractive index modifications on self-pulsation in these devices.
Vacuum-Ultraviolet Generation in CsLiB6O10
Authors: Umemura N. , Yap Y.K. , Mori Y. , Sasaki T. , Yoshida K. , Kato K.
Published: February 2023

In previous publication 1 , we have reported the vacuum-ultraviolet (VUV) generation down to 0.185 μ m in CsLiB6O10 by mixing the fifth harmonic of a Nd:YAG laser at 1.0642 μ m and the output of a KTP OPO pumped by the second-harmonic of the same Nd: YAG laser. However, no attempt was made to evaluate its performance for VUV generation at wavelengths longer than 0.19 μ m in this material. As a prior experiment, we have demonstrated the VUV generation at 0.1914 μ m by type-2 mixing between the fifth harmonic of a Nd:YAG laser at 1.0642 μ m and the output of a H2 Raman oscillator pumped by the same Nd:YAG laser. The phase-matching parameters tabulated in Table 1 were calculated with the Sellmeier’s equations and thermooptic constants reported in Ref.1. The 12-mm-long crystal used in this experiment was cut at θ ≃ 41 ° and ϕ =0 ° for type-2 second harmonic generation (SHG) at 0.5321 μ m. The entrance faces were polished with a flatness of λ /10 and no AR-coatings are applied for this crystal.
Second harmonic generation in periodically poled KTP pumped by a single longitudinal mode laser
Authors: Englander Avraham , Tzuk Yitshak , Glick Yaakov
Published: February 2023

Recently published second harmonic generation (SHG) conversion experiments with a periodically poled (PP) KTP crystal pumped by a multi-longitudinal mode (MLM) Q-switched laser show an efficiency curve which saturates at 65% [1]. This behavior does not fit the theoretical conversion model [2].
Dynamic energy transfer between fundamental and second harmonic with periodically poled KTP and a single longitudinal mode pump
Authors: Tzuk Yitshak , Glick Yaakov , Englander Avraham
Published: February 2023

It is well known that in the presence of non-ideal phase matching conditions, the harmonic generation process shows an oscillating energy transfer between the pump and the harmonic beams as a Junction of distance inside the crystal[1]. The oscillation period length is inversely proportional to the phase mismatch. A numerical solution of the coupled wave equations shows that when the nonlinear drive term
(ω
p
2d
e
f
f
2l2I
p
)is high, the period length is also dependent on the pump intensity In certain conditions, a monotonous raising of the pump intensity causes a periodic transfer of energy between the two beams When the doubling crystal is pumped by a pulsed laser, there should be a change in the temporal profile of the frequency doubled beam since the pulse intensity is temporally dependent. With a multi-longitudinal mode (MLM) laser this phenomenon is smeared out because each mode has a different phase mismatch Similarly, the diffraction of the beam and the spatial intensity dependence contribute to the smear and the effect cannot be observed.
Beam Quality Characterisation of Nanosecond Optical Parametric Oscillators
Authors: Lyons S.C. , Oppo G.-L. , Firth W.J. , Barr J.R.M. , Coia C.
Published: February 2023

We present a novel approach to the numerical modelling of pulsed nanosecond optical parametric oscillators (OPO’s). Our model expands upon a recent procedure [1] to consider the case of a nondegenerate, singly resonant OPO. A single partial differential equation describes the temporal and transverse variations of the resonated signal field and also accounts for diffraction, phase mis-matching and idler absorption. The pump and idler fields are reconstructed from the signal dynamics. The numerical integration of our single equation model is considerably faster than that of the corresponding three coupled equations.
The four-photon parametric superfluorescence induced by conical pump pulses in sodium vapour
Authors: Vaičaitis V. , Stabinis A. , Piskarskas A.
Published: February 2023

The investigations of parametric interactions under the conically focused pump beams are of broad interest mainly due to the possibility of efficient modification of the generated radiation divergence [1] significantly improving it’s spatial and time coherence.
Ultrafast Liquid Dynamics using Six-Wave Mixing
Authors: Lin S. , Andrews D.L. , Hands I.D. , Meech S.R.
Published: February 2023

Liquid dynamics and optical multi-wave mixing processes form two well established areas of research that are currently attracting much interest — both theoretically and experimentally. In this paper we draw together these two subjects and describe our recent work in the laboratory and our theoretical interpretation of the results so far obtained. We describe a phase-conjugated six-wave mixing technique and present results obtained from samples comprising thin liquid films of donor-acceptor substituted stilbene dyes. Our experiment utilises a pump-probe arrangement in which a transient anisotropic grating is created within the sample and then probed after a variable time delay by recording the second-harmonic radiation generated from the grating. The arrangement used follows that of the earlier work of Fiorini et al1 but our experiment is performed using a femtosecond Ti:Sapphire laser which gives us a temporal resolution of the order of 100 fs. This has allowed us to observe for the first time using this multi-wave mixing process the ultrafast dynamics of liquid reorientation, Fig. 1.
A Study of Quasi-Fhase-Matched Second-Order Nonlinear Effects in Optical Waveguides Using an Iterative Finite-Difference Beam Propagation Method
Authors: Chou Hsu-Feng , Wang Gin-Chung , Lin Ching-Fuh
Published: February 2023

Quasi-phase-matched (QPM) waveguide devices have been widely studied due to their flexible frequency conversion abilities and potential applications in many areas Some analytical analyses [1] have been done to model the QPM second-order nonlinear effects using both the plane-wave and non-depleting pump approximation. However, precise analytical modeling of those QPM devices is quite difficult when large or irregular geometrical variations exist and the depletion of the pump energy is not negligible Therefore, we propose an iterative finite difference beam propagation method (IFD-BPM) to model and study the QPM second-order nonlinear effects in optical waveguides.
A spectroscopic study of photorefractive CdTe:Ge
Authors: Ramaz F. , Farid B. , Briat B. , Shcherbin K.
Published: February 2023

Vanadium and Germanium are known to induce photorefraction in cadmium telluride [1,2]. Although the understanding of V-doping is well advanced at present, relatively little is known about Ge-doping apart from the fact that a GeCd3+ (ionic notation) defect has been identified by electron paramagnetic resonance [3,4]. We have measured the photoinduced changes of the absorption as well as the Magnetic Circular Dichroism (MCD) of two CdTe: Ge crystals with the hope to further identify the photorefractive centers and processes.
Nonresonant four-wave mixing in photorefractive semiconductors using picosecond parametric generator
Authors: Gudelis V. , Jarašiūnas K. , Delaye Ph. , Roosen G.
Published: February 2023

We report the first studies of photorefractive semiconductors by using a picosecond optical parametric generator (OPG). We perform nonresonant degenerate four-wave mixing (DFWM) in CdTe and GaAs crystals far away from the band-gap, while the previous studies of optical nonlinearities using parametric devices have been carried out only at the resonant fundamental transitions. Consequently, application of OPG for studied of nonresonant interaction opens a possibility for a direct investigation of the wavelength dependence of mid-gap impurity related photoexcitation as well as time-resolved measurements of carrier and space charge field dynamics.
Anomalously fast response of photorefractive lithium tantalate and niobate
Authors: Prudkovskii P.A. , Skugarevskii O.V.
Published: February 2023

It is well known that in photorefractive lithium tantalate and niobate, photoinduced light scattering (PHILS) and holographic-type parametric scattering (HTPS) [1] are possible. In PHILS light is scattered by a set of random holographic gratings, and HTPS is scattering by a subset of these gratings satisfying the four-wave phase matching condition. The characteristic time of recording such gratings is defined by the Maxwell time τm ~ε/4πσ (here ε is the dielectric function and σ the electric conductivity of the crystal), which can vary in LiNbO3 and LiTaO3 from some minutes to many hours depending on the pump intensity.
Phase Conjugation by Stimulated Brillouin Scattering in d-LAP
Authors: Clark T. M. , Lamb R. A.
Published: February 2023

Phase conjugation using stimulated Brillouin scattering (SBS) is usually investigated in liquids and gases due to the higher Brillouin gain and self-healing ability of these media. However, in the last decade there has been a drive to develop “all-solid state lasers” and the study of SBS in the solid state is a natural extension of this development. In most solid materials the Brillouin gain coefficient is small and the phonon lifetime long compared to the duration of the pump pulse, and therefore, SBS is an inefficient process. In a conventional focused geometry this leads to breakdown and permanent damage. However, there is a small number of non-linear crystalline materials which have high gains comparable to fluid media; deuterated L-arginine phosphate (d-LAP)1 is a well known example. In these materials efficient SBS may be induced and this leads to strong depletion of the pump beam in the focal region. This protects the focal region from high intensity and reduces the probability of damage.
Simulation and Experimental Analysis of a Phase Conjugating Correlator
Authors: Sharp J. H. , Budgett D. M. , Slack T. G. , Scott B. F.
Published: February 2023

The compact phase-conjugating correlator (PCC) devised by Duelli et al. [1] provides a compact and robust correlator design while being compact and insensitive to phase imperfections in the transform optics and spatial light modulator (SLM) commonly found in the more conventional Vander-Lugt correlator. This design has been allied to that of the hybrid concept described by Young et al. [2] to provide high-speed performance. The correlator is shown schematically in figure 1.
Modelling and Diagnostic of Pulsed Laser-Solid Interactions Applications to Laser Cleaning: a TMR programme
Authors: Oltra R. , Arenholz (AT) E. , Leiderer (DE) P. , Kautek (DE) W. , Fotakis (GR) C. , Autric (FR) M. , Afonso (ES) N. , Maine (FR) P.
Published: February 2023

This TMR programme ((ERBFMRXCT980188) aims to study the fundamental physical and chemical aspects of pulsed laser-solid interactions leading to any form of surface cleaning in order to develop the laser cleaning technique as a reliable industrial production tool.
On pulsed laser ablation of metals: comparing the relative importance of thermal diffusion in the nanosecond - femtosecond regime
Authors: Kapitan D. , Coutts D. W , Webb C.E.
Published: February 2023

In recent years numerous reports on pulsed laser ablation of metals using various laser sources have fostered the discussion regarding the limitations due to thermal diffusion to produce feature sizes on (sub-)micron scale smaller than the diffusion length. Particularly in the light of novel micromachining applications, the relative benefits of using pulsed nanosecond (ns) lasers in the visible, such as copper vapour lasers and frequency doubled Nd:YAG, versus femtosecond (fs) Ti:Sapphire lasers operating in the infrared, remains debatable.
Laser ablation using an ultrafast all-solid-state Cr:LiSAF regenerative laser amplifier system
Authors: Parsons-Karavassilis D. , Dowling K. , French P. M. W. , Taylor J. R.
Published: February 2023

Conventional continuous wave and long pulse (nanosecond) laser ablation is used in many fields, such as materials processing and medicine [1]. In these regimes the dominant process involved is the heating of the target material through the liquid phase to the vapour phase, resulting in expansion and expulsion of the desired target material. This is accompanied by heating and collateral damage to the surrounding area, the degree of which is determined by the rate of energy absorption and the rate of energy loss through thermal conduction in the material. This collateral damage is often detrimental and a limiting factor when high precision ablation is required.
Electrical Circulation System of the Working Media of High Pressure Lasers on Rare Gas Mixtures with Fluorine Molecules
Authors: Shuaibov A.K. , Shimon L.L. , Minja A.J.
Published: February 2023

Electrical circulation system of the working media of the lasers on rare gas fluoride (RF), molecules F2(D′-A′), atoms (F) and fluorine ions (F+) causes the minimum pollution of working mixtures in operating time of pulse-periodic lasers, is steady against application in agressive media and is characterized by minimum energy consumption.
Characterization of laser plasma plume for deposition of CNX films
Authors: Lančok J. , Jelínek M. , Bulíř J. , Grivas C.
Published: February 2023

Pulsed laser ablation of graphite in nitrogen atmosphere is one of the perspective technique for the preparation of CNX films and superhard β-C3N4 films. The study of ablation process is very important for optimalization of deposition conditions and CNX film properties.
Characterization of optical torque exerted on optical rotators in a single-beam gradient-force optical trap
Authors: Ohmachi Yoshiro , Hashimoto Masaharu , Yashiro Tomohisa , Kanai Akira , Higurashi Eijl
Published: February 2023

A laser beam can be used to rotate objects with artificial non-symmetrical structures(1). In this paper we present numerical results for optical torque exerted on the star- and cross-type rotators. We assumed the objects are subjected to a strongly focused fundamental TEMoo Gaussian laser beam. The optical force resulting from reflection and refraction at the surface of the objects was calculated using the ray-optics model. We studied star- and cross-type rotators (polyimide, n2=1.525) suspended in liquid (ethanol, n1=1.363). From the experimental and the numerical results, we quantified the damping factor and the static frictional torque of the rotators.
Graphite-Diamond Transformation Induced by High-Intensity KrF Laser Target Irradiation
Authors: Zvoiykin V.D. , Molchanov A.G. , Korol V.Yu. , Rozanov V.B. , Sychugov G.V.
Published: February 2023

Explosives or explosive-accelerated plane flyers can pressurize the examined material up to hundreds kilobars, but it is heated significantly by a shock wave. If a phase transition occurs during the sample loading, a high post-shock temperature will influence a new phase1. Laser irradiation of targets may produce ablation pressures in a multi-megabar range with temperature control by means of time profiling of a laser pulse or using an appropriate target design. This offers new opportunities in investigations of equation of state and phase transformations in compressed materials, in particular, diamond production by laser compression of graphite targets2.
Essentially Nonlinear Patterns in Active Optical Resonators
Authors: Staliunas K. , Slekys G. , Weiss C.O.
Published: February 2023

Although complicated light field structures appeared in recent experiments with nonlinear optical systems, the patterns observed so far could be interpreted either as transverse modes of the resonator, or as the simultaneous excitation of many transverse modes. This implies that the patterns were dominated by boundary effects, rather than by the nonlinearity of the medium. The active nonlinear systems, like lasers, could not maintain an arbitrary image in their radiation, nor to display the „ essentially nonlinear“ patterns. „Essentially nonlinear“ pattern formation of lasers as it is described by the complex Swift-Hohenberg equation [1], requires primarily a large Fresnel number of the resonator and simultaneously a high level of degeneracy of transverse mode families.
Spatio-Temporal Master Equation for Folded Resonators
Authors: Dunlop A. M. , Firth W. J. , Harkness G. K. , Wright E. M.
Published: February 2023

We recently presented a spatio-temporal master equation (ME) model for describing the evolution of optical fields in laser cavities [1]. This ME is a paraxial wave equation with a propagation operator explicitly dependent on the ABCD elements of the cavity. It exactly reproduces the cavity mode structure in the linear case, and gives excellent agreement with the more exact Huygens’ integral method when nonlinearity is added, e.g. for laser cavities containing a Kerr lens and a gaussian aperture [1].
Patterns in Synchronously Pumped Optical Parametric Oscillators
Authors: Sirutkaitis V. , Grigonis R. , Slekys G. , Staliunas K.
Published: February 2023

In the last years the parametric light interaction became the common and powerful method for generation of widely tunable radiation. Nevertheless the data on the spatial structure of the optical parametric oscillators are only few [1]. The understanding of the spatial structure formation is very important not only for practical use, but also due to theoretical prediction of existence of localized structures which can be important for signal processing [2].
Spatial Mode Analysis of Self-Adaptive Laser Oscillators
Authors: Crofts G. J. , Udaiyan D. , Damzen M. J.
Published: February 2023

Optical phase conjugation techniques have been widely investigated for the dynamic correction of intracavity phase distortions in laser systems. The beam quality and stability in conventional solid-state lasers can be degraded due to thermally-induced phase distortions in the gain medium [1]. This work describes an analysis of the self-consistent fundamental mode of a self-adaptive holographic resonator which can dynamically correct for internal phase distortions [2].
Development of High Beam-Quality CO2 Lasers Exceeding 20kVV and Industrial Applications
Authors: Habich Uwe , Bartels Heike , Henning Thomas , Loosen Peter , Hertzler Christoph
Published: February 2023

High-power CO2 lasers have various applications in the automotive industry, ship building, tube and pipeline welding, surface treatment and steel production. The demands on reliability, stability, uptime etc. are the same as for the standard laser devices at lower power levels.
High Pressure Operation of a Fast Axial Flow CO2 Laser with a Narrow Gap Slab Radio Frequency Discharge
Authors: Markillie G A J , Betterton J G , Baker H J , Hall D R
Published: February 2023

High peak powers, varying pulse lengths and fast repetition frequencies are all desirable features of CO2 laser beams for materials processing applications. Previous device configurations include the TEA laser, generating pulse lengths of ~l-5µs at a pulsed repetition frequency (PRF) to ~400 Hz, and radio frequency (RF) discharge excited diffusion cooled slab waveguide and fast axial flow lasers, which both offer both continuous operation and pulse lengths of 50-100 µs at 5kHz. However, recent developments in materials processing have led to an interest in devices that can deliver shorter pulses than the existing slab or fast flow lasers, but with a much higher PRF than the TEA laser. Fast pulsing of gas lasers requires the switch-off time of the laser to be short compared with the pulse length, a need that is often satisfied by an increase in intracavity pressure. Previous studies of diffusion cooled slab waveguide lasers have shown that operation is possible at high pressures, but that the required cooling of the narrow gap discharge limits efficient operation to pressures of ≤ 300 Torr.
Deep Levels Induced by Impurity Free Vacancy Disordering
Authors: Johnson N P , Helmy A S , Bryce A C , Marsh J H
Published: February 2023

The use of quantum well intermixing (QWI) as a post growth process to modify the bandgap in optoelectronic integrated circuits is an attractive alternative to regrowth and over-growth processes. Impurity-free vacancy disordering (IFVD) offers the potential advantage of fewer extra expensive processing steps compared to intermixing achieved via implantation and annealing, in addition to low optical losses.
Kinetic enhancement of copper vapour lasers for high-power, high-beam-quality output
Authors: Withford M J , Brown D J W , Carman R J , Mildren R P , Piper J A
Published: February 2023

Pulsed copper lasers have a unique capability to produce high average powers in the tens-to-hundreds of watt regime at high beam quality (near diffraction-limited) in the visible as required for a wide range of applications (of which laser micromachining is currently the most important). Elemental copper vapour lasers (CVLs) have a well 11-developed technology and have been scaled to very large volumes, but generally give lower electrical-to-optical conversion efficiencies and lower specific powers (especially at high beam quality) than the copper bromide or copper HyBrID versions.
Negative ions in plasma of pulsed metal and metal compound vapour lasers
Authors: Isaev A.A. , Markova S.V. , Petrash G.G. , Zemskov K.I.
Published: February 2023

Recently considerable improvement of characteristics of pulsed metal vapour and metal halide vapour lasers, such as copper vapour laser, CuBr-H2 and copper HyBrID laser, have been achieved. In [1,2] it was shown that this improvement can be qualitatively explained by the presence of HBr molecule. The influence of HBr can be explained by the process of dissociative attachment of electrons to this molecule which can lead to changes in the pulsed discharge development, recombination of plasma between excitation pulses and probably in electron energy distribution function.
Self-pumped phase conjugation in Ti:sapphire slab amplifiers
Authors: Minassian A. , Crofts G. J. , Damzen M. J.
Published: February 2023

Four-wave mixing experiments in flashlamp-pumped Nd:YAG [1] and laser pumped Ti:sapphire (Ti:S) [2] have been shown to have the potential for high phase conjugate reflectivities of grater than 100%. A gain medium in self-intersecting loop geometry can be considered a holographic laser resonator, in which a gain hologram written in the gain medium by the self intersection of the input beams forms a diffractively-coupled resonator in which the lowest-order mode is the phase conjugate. In this paper we present, for the first time, the experimental implementation of a self-pumped phase conjugate (SPPC) laser in transversely laser-pumped Ti:S slab amplifiers and discuss the characteristics of the resulting laser radiation.
Real part of resonant susceptibility and refractive index grating formation in inverted Nd:YAG
Authors: Antipov O.L. , Kuzhelev A.S. , Chausov D.V. , Vorob’ev V.A. , Zinov'ev A.P. , Luk'yanov A. Yu.
Published: February 2023

Absence of full knowledge on resonant susceptibility (RS) of laser crystals leads to underestimation of different nonlinear optical effects (such as holorgraphic grating formation and others) which are very important for understanding the complicated laser dynamics and construction of new laser architectures. In the majority of previous experiments the resonant wave mixings (using nonlinearity of saturation of the working transition) in inverted Nd:YAG are explained by the gain grating (GG) formation (sec. for example. [1]). On the other hand, it is well known, that pumped and unpumped laser crystals have different refractive indexes due to difference in polarizability of excited and unexcited Nd3 ions [2,3]. However. various investigation methods provide different values of the polarizability difference varying from 4.10−3nm3 [2] to 9.10−4 nm3 [3] for the well-studied Nd-dopcd materials.
Modified terahertz optical asymmetric demultiplexer for the extinction ratio enhancement of all-optical NRZ-to-inverted-RZ converter
Authors: Lee Hyuek Jae , Kim Kwangjoon , Kim Hye-Young , Choi Jee Yon , Kim Hae Geun
Published: February 2023

In future all-optical networks, it is likely that both WDM and OTDM will be incorporated, and there will be a need for all-optical data format conversion/reconversion between WDM and OTDM [1]. Nonretum-to-zero (NRZ) and retum-to-zero (RZ) formats are mostly used among a variety of data formats. NRZ format has the merit of lower bandwidth requirement and higher timing jitter tolerance than RZ format, while RZ format Is preferred in ultra-fest OTDM networks to make use of bit-interleaving technique. Some previous works have demonstrated NRZ-to- (inverted)-RZ converters using nonlinear optical loop mirror (NOLM) and cross-gain compression of semiconductor optical amplifier (SOA) [1]. NRZ-to-inverted-RZ converter based on cross-gain compression of SOA has the merit of simplicity in construction, though its extinction ratio (ER) is poor. To improve ER, we have serially added a modified terahertz optical asymmetric demultiplexer (TOAD) [2] to the converter. In this paper we propose and demonstrate ER enhanced NRZ-to-inverted-RZ converter.
Nonlinear Optical Properties of Czochralski-Grown Periodically Poled LiNbO3 Crystals
Authors: Gliko O.A. , Naumova I.I. , Ju J. J. , Kim H. K. , Cha M.
Published: February 2023

Bulk periodically poled LiNbO3 crystal is a promising material for nonlinear optical devices using quasi-phase matching In particular, frequency doubling of near-infrared radiation into the blue spectra range and optical parametric oscillation are of importance. The spatial modulation of the nonlinear susceptibility is realized in lithium niobate by formation of periodically reversed domain pattern. In this work the periodic domain structure was formed in LiNbO3:Nd:Mg crystals by means of the modulation of impurity incorporation during the process of crystal growth. We investigated the correlation of ferroelectric domains with Nd-concentration modulation, and the nonlinear properties of the optical superlattice.
High NA pump core double clad Nd:glass fibre laser
Authors: Plamann K. , Zellmer H. , Reichel V. , Unger S. , Tünnermann A.
Published: February 2023

Numerous applications in metrology, telecommunication, medicine and material processing require highly efficient and powerful yet reliable laser sources with excellent beam quality. In recent years, our group has focused on the development of rare earth doped glass fibre lasers pumped by commonly available near infrared laser diodes to provide laser sources meeting these requirements [1,2]. Any desired laser beam quality can be imposed by designing the waveguide structure of the fibre appropriately. Furthermore, using a double clad fibre design permits a power scaling almost exclusively limited by the output power of the available pump sources: the properties of an outer cladding are optimised in view of an efficient incoupling of the pump laser diode light.
Neodymium doped fiber power amplifier for coherent inter-satellite communication systems
Authors: Rochat E. , Haroud K. , Dändliker R.
Published: February 2023

In the context of free space communication systems, one needs laser beams of at least 1 W power modulated at GHz frequencies, usually delivered by a MOPA (Master Oscillator Power Amplifier) configuration. To allow coherent detection, a stable narrow band source is required, the polarization state must be stable and controllable at the amplifier output and the phase noise must be kept low. The master oscillator is a single frequency Nd:YAG laser emitting at 1.06 µm.
Modelling of FM and AM Mode Locked Er:Ti:LiNbO3 Waveguide Lasers
Authors: Sciancalepore D. , Balsamo S. , Montrosset I.
Published: February 2023

The generation of short optical pulses through mode locking of a laser by an internal phase or amplitude modulation is well known. In this paper FM and AM Mode Locking (ML) in Er:Ti:LiNbO3 fully integrated waveguide lasers [1] have been theoretically analyzed and compared.
A free-space optoelectronic crossbar interconnect with Terabit/s communication to silicon electronics
Authors: Fancey SJ , Forbes MG , Taghizadeh MR , Dines JAB , Buller GS , Walker AC , Desmulliez MPY , Pennelli G , Marsh JH , Stanley CR , Horan P , Byrne D , Hegarty J , Eitel S , Gulden KH , Gauthier A , Benabes P , Goetz M
Published: February 2023

It has been observed that the fundamental physical limit on communication rates between silicon CMOS chips may be lower than 1 THz for conventional metal lines of lengths - 10cm. This bandwidth limit scales as the aspect ratio (the ratio of total cross-sectional area to length) of the interconnect1. Since the off-chip bandwidth requirement of silicon ASICs is predicted to increase beyond 1 THz within five years, a potential bottleneck in computational performance can be foreseen. Free space optoelectronic connections show promise in overcoming the predicted bottleneck since they offer high spatial density connections (>106 per cm2) free of the aspect-ratio problem and many other limitations of electrical interconnections2.
Fabrication of test structures for 4x4 InP/InGaAsP Integrated Optical Matrix
Authors: Qian Y H , Bryce A C , Marsh J H , Wilkinson C D W , Owen M , Penty R V , White I H , Robertson M J
Published: February 2023

All-optical space switches are increasingly important for high performance optical communication networks and systems. A wide range of optical switches have been studied in recent years, but they remain costly or provide limited functionality. We report the fabrication technologies developed for a previously designed novel compact 1.5 μm InP/InGaAsP 4x4 integrated optical switching matrix measuring 1x2 mm2 in size.
Effects of Pump Radiation Polarisation on Stimulated Rotational Raman Scattering
Authors: Diso D. , Perrone M. R.
Published: February 2023

The tuning-range increase of the excimer laser radiation by stimulated Raman scattering is quite useful in many industrial and scientific application fields as in differential-absorption lidar systems for stratospheric and troposheric ozone measurements [1]. Stimulated rotational Raman scattering (SRRS) in H2 has recently been investigated with a XeCl laser beam to increase the tuning-range of excimer lasers [2]. The Raman shift in H2 is 4155.21 cm-1 and 588 cm-1 for vibrational and rotational scattering, respectively and then, rotational Raman scattering provides Stokes lines more closely spaced to the XeCl line (308 nm) with respect to vibrational Raman scattering. It is shown in [2] that energy conversion efficiencies to the first rotational Stokes S01 (314 nm) of about 35% were obtained in 30 bar of H2 by focusing a good-optical-quality XeCl laser beam of relatively low energy (14 mJ) and circularly polarised. The use of a focusing lens of 15-cm focal length was peculiar to get such high conversion efficiencies. In fact, with a circularly polarised pump beam a high-angle focusing geometry allowed to get only rotational Raman scattering as a consequence of gain suppression effects on vibrational Raman scattering, whereas a low-angle focusing geometry provided only vibrational Raman transitions.
High Power Diode-Pumped Tm-Doped Silica Fibre Laser in a Double-Clad Pumping Arrangement
Authors: Jackson Stuart D. , King Terence A.
Published: February 2023

One of the strong present interests is to produce high power laser radiation in the 1.9 μm region of the spectrum in order to satisfy a number of important medical applications such as surgery. Utilising the double-clad pumping geometry [1] in conjunction with diode-pumping allows one to generate conveniently high power laser radiation of both high efficiency and high beam quality. In addition, quasi-three level transitions such as the 3H4→3H6 laser transition of Tm3+ benefit greatly from the high level of pump and laser field confinement reletant to fibre lasers, which enables transitions that inherently have a relatively small stimulated emission cross section coupled with a possible large ground state reabsorption loss, to lase efficiently. Judicious design of the double-clad fibre is therefore required in order to extract the maximum output power and efficiency.
Polarisation control mechanism of DFB fibre lasers
Authors: Varming P. , Philipsen J.L. , Berendt M. O. , Lauridsen V. C. , Povlsen J. H. , Hübner J. , Kristensen M. , Pálsdóttir B.
Published: February 2023

Since the introduction of single-mode DFB fibre lasers with UV induced phase-shift, these lasers have found many applications within optical communication [1]. Single polarisation operation of the laser could be attributed to a polarisation dependence of either the grating reflectivity, background loss, erbium gain, or the phase-shift. It has been shown that a birefringent distributed phase-shift causes a considerable difference in the magnitude of the phase-shift experienced by the two polarisations [2]. However, until now it has not been clarified which polarisation dependent effect is dominating in obtaining single polarisation operation. In this paper, we present experimental evidence that a birefringent distributed phase-shift is the dominating effect.
Single-Transverse-Mode Amplifier Based On Multimode Er-Doped Fiber
Authors: Okhotnikov O.G. , Sousa J.M.
Published: February 2023

An improvement in scaling active fiber devices with single-transverse-mode output to higher power levels can be achieved through an increasing in mode-field area. A multimode core allows for a significant increase in mode volume. The gain of the given mode depends on the overlap between mode-field distribution and the spatial distribution of the gain within the multimode fiber core. Spatial distribution of the active ions was designed to provide maximum total gain for the fundamental mode while keeping the gain for the other modes below the level required for significant amplification. To study the effect of mode selection, three fibers were drawn from the same preform [1]. The fibers developed had a step-index design with Al as an index rising dopant, a fiber NA of 0.2 and core diameters of 4.5, 9.5 and 19 μm. The absorption for the fundamental mode in these fibers at 1.53 μm was measured to be 25, 37.5 and 47 dB/m, respectively. The overlap integral between the erbium distribution and mode fields was determined directly from absorption measurements [2] and then compared with the overlap calculated using measured Al and Er profiles. Figure shows the dependence of the overlap integral on the fiber V-number for an LP01 signal mode and higher-order modes. The curves show the overlap computed numerically. The overlap integral and therefore the gain are higher for the fundamental mode. The higher-order modes discrimination is significantly gained from high doping level. As expected and observed experimentally, increasing the doping level increases the modal gain difference and thus improves the fundamental mode selection.
Spectroscopy of localised and delocalised excitons in InGaN light emitting diodes
Authors: Martin R.W. , O’Donnell K.P.
Published: February 2023

Recent dramatic progress in research on InGaN based light emitters has led to the commercialisation of high brightness blue and green LEDs and announcements of room temperature lasers with lifetimes measured in thousands of hours. By altering the indium fraction the InGaN band-gap can be varied between 2.0 and 3.4eV and the tendency of the indium to segregrate leads to fluctuations of the band gap within any layer of InGaN. We show that light emission arises from the recombination of excitons strongly localised in deep potential wells associated with indium rich regions of the active region. An investigation of these localised excitons using absorption and luminescence spectroscopies applied to InGaN single quantum wells in commercial LEDs provides important insights into the mechanics of the light emission.