bluuebunny/crossref_metadata_2025 huggingface dataset:
Fundamental features of femtosecond Maxwell optical solitons
Authors: Serkin V. N. , Shmidt E. M. , Samarina E. V. , Belyaeva T. L.
Published: February 2023

It is well known that the picosecond time duration range optical solitons dynamics described by the nonlinear Schrodinger equation (NSE) has provided remarkable accord between theory and experiment. There is a gap of understanding as to the fundamental features of solitons when going to the femtosecond range and the envelope contains only a few optical periods. Up to date no answer has been obtained to the key question of the nonlinear optics of femtosecond pulses. This question is what is the ultimate width of a pulse that can be produced and how to produce pulses with the width t = T, that is, optical videopulse without a high-frequency field component?
The supersonic chemical oxygen-iodine laser—achievements and perspectives
Authors: Barmashenko D. , Elior A. , Lebiush E. , Rosenwaks S.
Published: February 2023

We report on extensive experimental and theoretical investigations of the supersonic chemical oxygen-iodine laser (COIL). The interest in the COIL lies in the enormous storage capacity of its chemical constituents, amounting to several megajoules per liter, as well as in the fact that it emits at 1315 nm, a very useful wavelength for fiber optics. The laser transition takes place between the spinorbit levels of the ground state configuration of the iodine atom where the upper level is populated by near resonant energy transfer from an electronically excited oxygen molecule: O2(1Δ) in the gas phase, at nearly 100% yield in the Torr range, is produced by a gas-liquid reaction of Cl2 gas with basic hydrogen peroxide solution.
Cathode hot spots and their influence on the discharge in a XeCl laser
Authors: Timmermans J. C. M. , van Goor F. A. , Witteman W. J.
Published: February 2023

For the 1-kW XeCl laser being developed by NCLR,1 the efficiency and smoothness of the discharge are very important. Arcing at a repetition rate of 1 kHz would result in rapid electrode erosion. To study the onset of streamers and arcs we investigate the discharge with a 10-ns gated CCD-camera. Observations show that instabilities start as hot spots on the cathode. From these hot spots plumes arise that diffuse into the homogeneous bulk discharge. The cathode layer, the distance from the cathode to the point where the plumes vanish into the homogeneous part, grows exponentially in time. The plumes individually contract, and finally develop into an arc.
Influence of modulation and fringe velocity on the photorefractive response with moving gratings in Bi12SiO20
Authors: Brost George A. , Magde Kevin M. , Cartwright Colin , Gillespie W. Allan , Wang Zhaoqi
Published: February 2023

Hologram recording by a moving interference pattern in a dc-electric field can provide large enhancements in the photorefractive effect in crystals with long drift lengths, such as semiconductors and the sillenites. The theory of Refregier et al.1 predicts the photorefractive response, but only in the limit of small modulation. In practice, most experimental conditions cannot be adequately described by the linearized theory. The correction function used by Refregier et al.1 describes the effect of modulation, but only for two-wave mixing at the optimum velocity. Au and Solymar2 have demonstrated numerically a complicated photorefractive response. In this paper we provide more detailed numerical analysis, and for the first time, experimental characterization of the photorefractive response, including both diffraction and energy transfer, in BSO as function of modulation index and fringe velocity.
Characterization of micro- and optoelectronic devices by ultrafast optical techniques
Authors: Roskos Hartmut G.
Published: February 2023

Ultrafast optical techniques continue to gain acceptance for the characterization of high-speed micro- and optoelectronic devices and circuits. In this talk, the most important optical measurement techniques are described and their status critically reviewed.
Fast-tuned high quality beam CO2 laser operating in continuous and pulse-periodic mode with average power up to 2.5 kW
Authors: Grachev G. N. , Ivanchenko A. I. , Ponomarenko A. G. , Shulyat'ev V. B.
Published: February 2023

A laser has been created on the basis of the continuous electric-discharge CO2 laser with a cross gas flow of the LOK-series.1 A gas-discharge chamber1 has 2 discharge gaps that are formed by a common plane anode which is placed in the central part of the gas dynamic channel and 2 cylindrical cathodes being arranged on both sides of the anode close to the channel walls.
Analysis of chirp and spectral width of ultrashort light pulses in the nonlinear pulse-width meter
Authors: Kabelka V. , Masalov A. V.
Published: February 2023

Intensity profile of ultrashort (ps and fs) pulses is only the part of information necessary in the analysis of propagation effects and light-matter interaction. Spectral information (phase modulation, instantaneous frequency, spectral distribution, chirp, etc.) is the other part required in the characterization of pulses. Nonlinear pulse-width meter such as noncollinear second harmonic generator, is successfully used in measuring pulse envelope in ps and fs scale.1 The idea to combine noncollinear meter with the spectrograph was realized in FROG technique2 where the whole (intensity and phase) temporal profile of pulse were retrieved. In our paper3 we have shown that in the pulsewidth meter based on noncollinear second harmonic generation the spectral information of pulse is presented in second-harmonic beam divergence. In the present paper we show that in the pulsewidth meter based on self-diffraction process (used in FROG technique) the divergence of self-diffraction beams contains enough spectral information to restore the chirp of pulses.
Power limiting and temporal break-up in self-mode-locked lasers
Authors: Cormier Jean-François , Piché Michel , Salin François , George Patrick , Watson Jennifer
Published: February 2023

Self-mode-locking of solid-state lasers is now established as the most powerful method to generate femtosecond optical pulses.1-4 Best results reported so far3,4 were obtained with Ti:sapphire lasers where pulse durations down to 10 femtoseconds were achieved. Self-modelocking is attributed5 to Kerr lensing (selffocusing) in the gain medium or in other intracavity materials; in properly designed cavities, Kerr lensing has the effect of reducing the diffractional losses or of improving the overlap between the pump and laser beams. Under such circumstances, Kerr lensing produces a nonlinear gain favoring the growth of intense short pulses at the expense of multimode (cw) oscillations. It is known experimentally3 that high-power, self-mode-locked lasers switch from one-pulse to two-pulse emission. In this paper, we analyze the large-signal response of nonlinear cavities in order to understand the stability range for one- and two-pulse emission.
Graded-reflectivity profile to be used in an unstable resonator for a specified output
Authors: Bélanger P.-A. , Paré C.
Published: February 2023

The advent of lossless graded-reflectivity mirrors (GRMs) is now widely recognized as an important headway in the field of optical resonators.1 When used as the feedback output mirror inside an unstable resonator cavity (Fig. 1), a GRM greatly improves the quality of the nearfield by yielding a wide beam with reduced ripples thanks to its tapered edges. In contrast, the more conventional unstable cavity yields an annular output beam with hard-edge truncation and disappointing beam quality for near-field applications.
Beam cleanup and beam combining using stimulated Raman scattering
Authors: van den Heuvel J. C.
Published: February 2023

Beam cleanup1 and beam combining2 depend strongly on the geometry of the interaction volume of the Raman amplifier. During the propagation of the TEM00 Stokes seed, the amplification by the multimode pump beam generates many additional high order modes. However, due to the propagation through the interaction region, these higher modes are filtered away since only the modes that fall within the solid angle determined by the geometry are amplified. Therefore, focused beams are investigated in order to have a geometry with a low Fresnel number.
A pulsed two-wavelength self-injection locking controlled Ti:sapphire laser
Authors: Deneva M. , Stoykova E. , Gizbrekht A. , Nenchev M.
Published: February 2023

The potential of the Ti:sapphire lasers for applications in spectroscopy and differential absorption lidar measurement can be essentially improved when the lasers operate simultaneously at two independently tuned wavelengths.1-3 Recently, we have demonstrated that for the cw Ti: sapphire laser, a passively self-injection locking technique4 is an attractive way to realise this mode of operation. We applied here this technique in novel schemes to obtain efficient two-wavelength operation for a pulsed Ti:Al2O3 laser, pumped with a 0.53µm harmonic of Nd:YAG laser (Ep~4 mj), Δτp ~ 15 ns). The control is produced by reinjection of a small part (~0.003%) of the cw output back into the non-selective cavity at two wavelengths after the spectral filtering.3 The two-wavelength laser arrangements used are given in Figs, 1a, 1b, and 1c. They have as a principal part a two-outputs Kogelnic-type concave mirrors (mc1,mc2)—flat mirrors (MO,Me) cavity with a longitudinally pumped 1-cm-long 5×5 mm cross section Ti:Al2O3 crystal. The one laser output, this from the flat mirror Me (R = 70%), is reinjected back at two selected wavelengths λ1, and λ2 by the two wavelength retroreflector TWR, based on the Interference wedges (IW, and IW2);5 wedge thickness ~5µm, reflectivity of the coatings R1 = R2 = 0.9, and the wedge angle α = 5.10–5 rad. The wedge transmission at resonant wavelength is ~0.7. In the schemes used, a single interference wedge acts as a tunable spectral filter for one wavelength (which is resonant for the wedge thickness of the incident part) and as a coupler for the second wavelength λ2, selected by the second wedge IW2. In the first arrangement (Fig. 1a), which is similar to this applied by us for the cw laser,3 the retroreflection is in coincident beams.
Adaptive optical mirror for unstable resonators with thermal effects
Authors: Pavel N. , Dascalu T. , Totia H. , Florescu R. , Lupei V.
Published: February 2023

The generation of high energy, diffraction limited laser beams from the solid-state laser is of great interest for various scientific and industrial applications. Unstable resonators equipped with variable reflectivity output mirrors (usually a super-Gaussian profile) were demonstrated to be the best solutions for these demands.
Obtaining of prescribed-profile beams from a laser with stable (unstable) resonator and graded reflectance mirror
Authors: Matizen Y. E.
Published: February 2023

The standard approach to developing new laser resonators with graded reflectance mirrors is based on solving the direct problem of finding the resonator fields for given mirror reflectance function.1 As a result the output beam profiles and intracavity fields do not generally meet the application needs.
The investigation of thermal focusing in flash lamp pumped pulse Cr:Tm:Ho:YAG laser
Authors: Jabczyński J. , Jankiewicz Z. , Zając A. , Žendzian W.
Published: February 2023

The output energy and range of the pump power of a flash lamp pumped pulsed Cr:Tm:Ho:YAG laser is limited by thermal phenomena. As was shown in Ref. 1, with increasing pump power from a given value, the output energy and efficiency decreased till the generation broke off. This effect, caused by a temperature increase in the laser rod, can be explained alternatively by the increase of population of lower laser level belonging to the ground level multiplet or by increase of diffraction losses due to thermal focusing. It was shown that for practical cases [see Refs. 1 and 2], the thermal relaxation constant was about 1 s for YAG rods, so in the case of pulse repetition frequency >5 Hz the temperature gradients in the rods are stationary. Due to lower transfer efficiency and higher threshold in comparison to Nd:YAG, thermal focusing in Ho:YAG is much stronger. The main aim of our work was to investigate dependencies of divergence and beam quality of Ho:YAG laser on pump power.
Modelling of dynamic behaviour of blue lasing in praseodymium doped dielectric waveguide structures
Authors: Szczepański P. , Mossakowska-Wyszyńska A. , Malinowski M. , Łuczyński Z. , Łukasiewicz T. , Frukacz Z.
Published: February 2023

The renewal of interest in study praseodymium (Pr3+)-doped solid state materials is due to the emission spectrum of this ion extending from ultraviolet1 (UV) to near infrared.2 Laser action in several Pr3+ -doped crystals: LiYF4, YAlO3, as well as fibres has recently been reported.3 Especially the blue-green part of the Pr3+ emission spectrum is very interesting, since there is a great need for compact, integrated laser sources for many applications such as data storage, display technology, undersea communications, and optical processing.
Computer simulation of a miniaturized end-pumped laser rod
Authors: Altmann K. , Yahel R. Z. , Hallddrsson Th.
Published: February 2023

A simulation program was developed by combination of a finite element code (FEM) and a 3-D beam propagation code (BPM) to analyze thermal effects on the mode formation in miniaturized diode pumped solid-state lasers. Numerical results were compared with analytical formulae, and were found to be in very good agreement for cases allowing an analytical treatment.
Laser excitation sources for chromium-doped forsterite: a comparative study
Authors: McKirmie I. T. , Gloster L. A. W. , Jiang Z. X. , King T. A.
Published: February 2023

In this paper we report a comparative study of the performance of chromium-doped forsterite lasers pumped by a range of pulsed lasers. The results include the first feasibility studies of ultraviolet excitation and ruby laser pumping. Chromium-doped forsterite laser performance is assessed with three other sources: first and second harmonics of Nd:YAG and titanium-doped sapphire.
Modeling of SHG and OPO performance
Authors: de Winter L. , Keijzer F. , Boersma R. , Bente E.
Published: February 2023

The efficiency of SHG and OPO operation for high rep-rate, high-averagepower laser beams is investigated. This efficiency depends on both laser and crystal parameters. For instance, for the OPO there are variable parameters such as input energy, length of the crystal, cavity length, seed power, crystal sort, etc. Emphasis is put on the effects of the thermal load of a BBO crystal.
FIRAM® modification suitable to mid- and far-IR regions
Authors: Aleksandrov I. V. , Arkhireev V. O. , Nesterova Z. V. , Nesterova V. A.
Published: February 2023

It is well known that the multiple visible Stokes generation due to stimulated Raman scattering (SRS) of high-intensity ultrashort light pulses in long optical fibers (OF) could be realized. But the most effective parametric transformation of pump pulse energy in silica OF was demonstrated when the "phase-capture” regime for the same pump and Stokes pulses took place during the dynamic core index change by intensive picosecond light fields.1 The whole number of Stokes SRS components in that case exceeds 20. Unfortunately, the Raman gain is diminished from the visible to the IR region and, as a rule, other nonlinear processes (for example, self-phase modulation and 4-photon mixing) became preferable in silica OF.
New aspects on multichromophoric laser dyes
Authors: Verseckas A. , Menzel R. , Thiel E. , Drexhage K. H.
Published: February 2023

Multichromophoric (antenna) dyes (MCD) are frequently discussed as potential high-efficiency laser media. Appropriately designed MCDs have the potential to completely absorb the pump light already at a low concentration. The correspondingly low reabsorption of laser light should permit a much more efficient lasing action than in the parent dye. However, so far this expectation was not borne out by experiments.
On the feasibility of 1.5 µm laser emission in concentrated Er systems
Authors: Lupei V. , Georgescu S. , Grecu S.
Published: February 2023

Laser emission in the 1.5-1.6 µm range is important for fiber optic communications. A major candidate as an active ion is Er3+, whose emission from the first excited level falls in this region. Since at high Er concentrations an efficient up-conversion (with rate P1) takes place, depopulating the emitting level (4I13/2), only very diluted Er systems were considered.
Third-order optical nonlinearities in ZnCdSe/ZnSSe multiple quantum well
Authors: Tanahashi I. , Manabe Y. , Hayashi S. , Yoshida M. , Mitsuyu T.
Published: February 2023

MQWs with II-VI compound semiconductors such as ZnSe/ZnS, ZnTe/ZnSe, and CdSe/ZnSe are promising materials for optoelectronic devices.1 Because of a large exciton binding energy due to a small exciton Bohr radius of II-VI compound semiconductors,2 the stable exciton peak can be seen at room temperature in II-VI MQWs. These MQWs have the potential to show large optical nonlinearities. Here, we report on the characterization and third-order nonlinear optical properties of ZnCdSe/ZnSSe MQW fabricated by MBE.
Quadratic nonlinear properties of poled glasses
Authors: Russell P. St. J. , Kazansky P. G.
Published: February 2023

Until fairly recently, second harmonic generation in specially treated glasses and glass fibres has been more of scientific that of practical interest, owing to the low attained levels of induced nonlinearity (several orders of magnitude less than in lithium niobate). During the past three years, however, a number of glass poling techniques have emerged that produce second order nonlinearities approaching 1 pm/V. Such high levels of nonlinearity are sufficient to be useful for parametric frequency conversion and electro-optic light modulation. These new poling techniques are: thermal poling of fused silica1-3 at 250-300°C under an applied electric field (the second-order nonlinearity appears in a thin layer just under the anode), thermal poling of tellurite glasses,4 corona poling of glass waveguides,5 and charge implantation by exposure to an electron-beam.2,6
Linear array performance based on Si:As blocked impurity band (BIB) IR detectors
Authors: Sinitsa S. P. , Frantsuzov A. A. , Esaev D. G.
Published: February 2023

An additional undoped layer (blocking layer) formed in the extrinsic photoconductive IR detector allowed to increase the amount of donors in the IR-active layer without increasing dark current.1 It permits to construct the focal arrays with high responsivity, signal-to-noise ratio, and insensitive to ionizing radiation.2
Generalised ABCD matrix formalism for lasers with radially varying gain
Authors: Gatz S. , Herrmann J.
Published: February 2023

Several authors have studied the properties of resonators with radially varying gain in parabolic approximation introducing complex-valued ABCD matrix elements. According to this theory even small effects or large pump beam sizes should cause even strongly geometrical unstable resonators to become stable against perturbations with confined modes.1 However, the parabolic approximation yields an overestimation of the gain guiding effect and gives no direct information whether a mode for a given cavity design can be generated or not.
Three-core ARROW-type diode laser: novel high-power, single-mode device, and effective master oscillator for flared antiguided MOPAs
Authors: Zmudzinski C. , Botez D. , Mawst L. J. , Nabiev R. F.
Published: February 2023

ARROW-type diode lasers have demonstrated high single-mode powers (0.5 W)1 in stable beams due to strong intermodal discrimination coupled with a large index-step (~0.05) and a relatively large spot size (4–6 μm). In order to obtain even higher single-mode powers we propose a three-core ARROW device for which high-order-mode suppression is obtained primarily via high interelement loss. Intermodal discrimination values as high as 18 cm−1 are obtained while the fundamental-mode loss increases by only 2–3 cm−1. Furthermore, when employed as the MO for flared antiguided power amplifiers,2 the MOPA near-field intensity profile is uniformized.
Multistability in grating tuned external cavity semiconductor lasers
Authors: Yan C. , Wang X. , McInerney J. G.
Published: February 2023

External optical cavity configurations are applied to semiconductor lasers for a variety of purposes: to study fundamental aspects of the laser dynamics (notably coherence collapse and chaotic phenomena), and to produce linewidth narrowing, mode-locking, bistability, and longitudinal or transverse and mode selection. Bistability has already been observed and studied in grating-tuned external cavity semiconductor lasers, and here we address the more general issue of multistability in these systems. We demonstrate that multistability can exist, and analyse the stability properties of the multistable solutions using static and dynamic models (the latter only in the limits of very weak and very strong feedback). Using the resulting stability criteria, we propose and demonstrate a novel method of exciting the multistable solutions to achieve controllable and possibly useful multistability.
Franz-Keldysh effect in an optical waveguide containing a resonant tunneling diode
Authors: McMeekin S. G. , Taylor M. R. S. , Vögele B. , Ironside C. N.
Published: February 2023

We report on work concerned with the optoelectronic properties of a GaAs optical waveguide containing a resonant tunneling diode (RTD).1 As far as we are aware this is the first report of an RTD directly incorporated in an optical waveguide and the observation of optical modulation via a Franz-Keldysh shift on the band edge. Figure 1 shows a cross-section schematic of the device. The device that was employed for our Franz-Keldysh band-shift measurements consisted of a 4-μm-wide optical waveguide with a 200-μm-long contact on top of the waveguide defining an active area of 800 μm2. Figure 2 shows the IV curve for this optical waveguide RTD. Resonance was found to occur at a bias of 0.9 V with a sharp drop in the current indicating bistability but not oscillation. Optical characterisation was carried out with the aim of determining the change in the optical absorption spectrum when the device switched. Optical characterisation of the device employed a Ti:sapphire laser that was tuneable in the wavelength region close to the band-gap resonance of the waveguide, i.e., close to 890 nm. In order to minimise thermal effects in the RTD a pulsed power supply was used. When the pulse amplitude exceeded Vb the current through the RTD would switch rapidly from Ib to Ic (see Fig. 2). An increase in absorption along the length of the RTD was observed upon switching due to the RTD. No change in absorption was observed when the device was biased below Vb.
Tunable bandpass fibre-optic filters utilising polymeric overlays for use in fibre lasers
Authors: Fawcett G. , McCallion K. , Johnstone W.
Published: February 2023

A bandpass filter based on coupling from a fibre, side polished beyond cut-off, to a planar polymeric waveguide is demonstrated. The filter exhibited a minimum linewidth of 13 nm, a tunability of 100 nm, and insertion losses as low as 0.5 dB.
Travelling-wave parametric generation in LBO with microjoules pump pulses
Authors: Banfi G. P. , Danielius R. , Di Trapani P. , Piskarskas A. , Righini R. , Solcia C. , Torre R.
Published: February 2023

Travelling-wave optical parametric generation (TOPG) is a simple approach to add tunability to fixed frequency ultra-short pulses.1 For many applications, it is desirable, beside preserving the short duration of the pump for the tunable pulses, to operate TOPG with a pump energy as low as possible.1 To this end, the temperature-tuned LBO in noncritical phase­matching appears favoured in comparison to other crystals.2 While the small group velocity dispersion (GVD) make LBO quite suitable in the femtosecond regime, as we already showed with 200-fs pulses,2 the large acceptance angle allows a tight focusing of the pump,3 and then to achieve the high intensities required by TOPG with modest energy, as shown in the following.
Optical and laser properties of the new laser crystals RE3+:Ca2Al2SiO7 (RE = Nd, Ho, Tm, Er)
Authors: Viana B. , Britos N. , Lejus A. M. , Teisseire B. , Vivien D.
Published: February 2023

In recent years, considerable interest has been devoted to the laser emitting in the 1.5–2 μm range. Ho3+ and Tm3+ operate around 2 μm while Er3+ covers the 1.5 μm range. The development of high power laser diodes lasing around 0.78 and 0.98 μm allows the pumping of these ions. Engaged in the search for new laser materials, we are interested by the gehlenite Ca2Al2SiO7 (CAS) matrix. In this matrix, there is an inhomogeneous broadening of the optical lines because of a structural disorder arising from the statistical distribution of Si4+ and half of the Al3+ ions on the same kind of tetrahedral sites. This host presents also high phonon frequency leading to short lifetime values when the energy gap difference between the emitting level and the one just below is small. Therefore, for the ions studied only the 4F3/2 level for Nd3+ (τ = 280 μs), 4I13/2 for Er3+; (τ = 7.6 ms) and 5I7 level for Ho3+ (τ = 7.4 ms) present lifetime values in the hundred of microseconds to millisecond range. Laser rods of the RE3+-doped CAS have been obtained by the Czochralski process.
Polarisation self-switching enhancement in a vertical-cavity surface-emitting laser by transverse mode saturation
Authors: Badr N. , White I. H. , Tan M. R. T. , Houng Y. M. , Wang S. Y.
Published: February 2023

High-speed polarisation self-switching has already been successfully demonstrated in external-cavity semiconductor lasers1,2 and in an AlGaAs/GaAs verticalcavity surface-emitting laser (VCSEL)3 using external cavity feedback. Theoretical studies predict that this process could reach ultrahigh operation frequencies of tens of gigahertz.4 Applications for such high-speed switching include all-optical clocking, optical interconnects, and integrated optoelectronic circuits.
Interaction of short laser radiation pulses with pigmented granules
Authors: Pustovalov Victor K. , Khorunzhii Igor A.
Published: February 2023

Heterogeneous pigmented biotissues contain spherical and spheroidal melanopro- tein granules of characteristic size about 1 micrometer. During the action of laser radiation pulse on pigmented biotissues the granules selectively absorb radiation energy whereas the surrounding biotissues have a markedly smaller absorptivity. Since the granules are the main radiation energy absorbers in the pigmented layers, the thermal processes with the lowest energy threshold is apparently initiated on the granules.
Investigation of wet field thermal effects of holmium (2,09 mkm) endolaser in rabbit eye
Authors: Danilichev V. F. , Boiko E. V. , Smirnov N. N. , Berezin Yu. D. , Monahov B. V. , Lazo V. V.
Published: February 2023

To evaluate the potential hazard of retinal damaging we studied in vitro and in vivo (on rabbit eyes) wet field thermal effects of pulsed Ho:YAG endolaser equipped by quartz fiberoptic 400 mm in diameter. Pulse duration was 1 ms, repetition rate 3 Hz. Used energy levels were between 5 and 300 mj per pulse. The thermocouple tip was placed on different distances from endolaser tip, and temperature was measured on various power rates and time intervals. Using multiple regression analysis, the model of fluid temperature rise dependence from energy per pulse, number of pulses and distance from endolaser tip was constructed.
Nearly-ideal Au/Pt-n-(p+n-) AI0.48ln0.52As Schottky contacts with a barrier height of 1.09 eV for high-speed photodetectors and transistors
Authors: Stareev G. , Fricke A. , Sowada D. , Kummetz T. , Mähnss J. , Kowalsky W. , Ebeling K. J.
Published: February 2023

During the last years significant efforts have been made to increase the Schottky barrier height in various InP devices such as high-speed photodetectors and transistors. Chu et al.1 found that the barrier height ϕBn of contacts to n-type InAlAs is independent of the choice of the metal and given by ϕBn = 0.61 eV. Oppositely, Sadwick et al.2 observed a pronounced influence of the kind of the metal on the barrier height with a highest ϕBn. value of 0.72 eV for Pt contacts. Such data dispersing imply that the treatment of the semiconductor surface is of primary importance. We demonstrate that the quality of Au/Pt-n-AlInAs Schottky barrier diodes can be improved, if low energy (30 eV) Ar+ bombardment for 1 min prior to the metal evaporation and proper rapid thermal processing (RTP) for 20 s are used. Experiments were performed onto 1.5 µm-thick Si-doped AlInAs layers with a donor concentration of 2 × 1016cm−3 grown by MBE. Some wafers were subjected to shallow (20 nm) Zn diffusion. Pt/Au Schottky contacts with diameters of 500 µm were fabricated in a procedure similar to the method described elsewhere.3 Figure 1 presents barrier heights of Au/Pt-n-AlInAs contacts as-deposited and after subsequent RTP at temperatures ranging from 230 to 430°C. Prior to any heat treatment the chemically cleaned and ion-etched contacts exhibit barrier heights of ϕBn = 0.82 eV and ϕBn = 0.85 eV, respectively. The annealing has no significant effect on ϕBn if the surface is only chemically precleaned, but gives a drastic enhancement of ϕBn for ion-etched diodes. The highest value of ϕBn = 1.09 eV is obtained with RTP carried out at 400°C. In our opinion, this is the largest ever reported value of ϕBn for AlInAs. The distinguished increase of ϕBn is due to the formation of a thin interfacial PtAs2 layer,4 which results from thermally stimulated As outdiffusion towards the metal. This subtle reaction is obviously suppressed by native oxides in chemically precleaned samples. The ion process used introduces negligible subsurface damages since the starting ϕBn values for chemically and ion-cleaned wafers are similar.
Optical properties and lineshape analysis of II-VI compounds obtained by spectroscopic ellipsometry
Authors: Jans J. C. , Petruzzello J. , Gaines J. M. , Olego D. J.
Published: February 2023

Developments in the use of wide-gap II-VI semiconductor materials have recently led to the demonstration of blue-green diode laser action in ZnSe-based heterostructures.1,2 We have used spectroscopic ellipsometry to investigate the optical constants of several II-VI compounds involved in the realisation of such laser devices. Ellipsometric modelling has allowed access to the above and below bandgap optical constants of the films involved. Thin films of ZnSe, ZnSSe, ZnCdSe, and ZnMgSSe grown by molecular beam epitaxy (MBE) on GaAs were compared. The alloy composition (S, Cd, and/or Mg content) of the compound materials has been varied and variations in the energy position of the interband transitions with alloy composition were observed. Lineshape studies were performed and data for the optical interband transitions in the films mentioned were obtained. The position and presence of the optical interband transitions E0, E0 + A0, E1 and E1 + Δ1 in the measured data for the ZnSe films is in good agreement with data available on bulk material and with recent data for thin films.3 Our results for the optical behaviour of the ZnSe films are in reasonable agreement with data obtained from a simplified model of interband transitions for single crystalline non-doped ZnSe bulk material available in recent literature.3 This model allows a further parametrisation of optical response for the films. Lineshapes of MBE-grown ternary and quaternary II-VI compound films were studied for the first time. Figure 1 shows the lineshape results for a ZnS0.15Se0.85 film on GaAs. Best fit results were obtained using an excitonic lineshape.4 Figure 2 shows an evaluation of the E0, E0 + Δ0, and E1 E1 + Δ1 interband transitions with change in alloy composition for the ZnSSe films examined. Similar results were obtained for ZnCdSe and for ZnMgSSe thin films.
A precision multiple beam system for the fabrication of large area, reticulated IR detector arrays
Authors: Hazell M. S. , Jones R. , Todd M. A. , Watton R.
Published: February 2023

The basic technique for the manufacture of laser reticulated IR detector arrays, by means of KOH assisted UV laser etching, has been described in earlier work in which the individual elements of the array are reticulated by a set of orthogonal grooves cut by a single UV laser beam focused to a diffraction limited spot.1 The maximum area of array that can be fabricated is governed by the cut speed (typically 500 µm/sec) and the period during which the ceramic can be immersed in the KOH without degradation. These parameters combine to prevent all but relatively small area arrays being fabricated using a single beam. This problem can be overcome by the use of a multiplexed system in which multiple focused beam substrate illumination is generated. This paper describes the design and application of the optical system that has been developed to deliver such an illumination distribution.
Fabrication and properties of chirped fibre gratings with reflection bandwidtbs exceeding 50 nm and narrow bandpass fibre grating filters
Authors: Sugden K. , Bennion I. , Molony A. , Fames M. C. , Reid D. C. J. , Goodwin M. J.
Published: February 2023

Fibre gratings with broad reflection bandwidths have many applications in fibre optic systems including dispersion compensation elements1 and external cavity reflectors for mode-locked lasers.2 A large reflection bandwidth may be achieved from a uniform period grating with a very strong coupling coefficient? However, we must also distinguish between those applications which demand only the broad bandwidth, and those which utilise the spatial dependence of the peak reflected wavelength as occurs in a grating with chirped period: applications specified by Refs. 1 and 2, for example, largely fall into this category. Despite the undoubted interest in chirped fibre gratings, very little has been reported on their fabrication and characterisation.
Laser telescope with overall compensation via phase conjugation of the output beamlet
Authors: Leshchev A. A. , Semenov P. M. , Vasiľev M. V. , Venediktov V. Yu.
Published: February 2023

We for the first time inform on the laser with the telescope, forming the output beam, in which all the elements of the output beamlet are included into the loop of compensation via phase conjugation. In such a system, distortions of the primary mirror are compensated as in the system with two auxiliary subsystems (nonreciprocal systems),1-3 while that of the secondary mirror—as in the system with diffraction structure on the mirror surface.4,5
Conjugate wave selection in four-wave mixing with feedback in a long nonlinear medium
Authors: Betin A. A. , Kirsanov A. V.
Published: February 2023

One of the efficient methods of phase conjugation (PC) is the four-wave mixing with feedback (FWMF) (Fig. 1). To select the wave conjugate to the input radiation in a FWMF resonator, it has been suggested to use either an inhomogeneous phase plate or a long (larger than the length of the longitudinal inhomogeneity of the signal) nonlinear medium.1 The diffraction efficiency of a thick hologram and its noises for a plane reference wave are calculated in Ref. 2. This paper provides the calculation of the power of the conjugate and noise waves produced by the reflection from a long phase hologram (mirror) recorded by two speckled beams. The paper also deals with experimental realization of a PC FWMF speckled beam in a long medium.
Comparison between continuous-wave and pulsed photorefraction in barium titanate
Authors: Barry N. , Duffault L. , Troth R. , Ramos-Garcia R. , Damzen M. J.
Published: February 2023

The presence of shallow traps1,2 and hole-electron photoconductivity3,4 in recent models of photorefraction in barium titanate account for much of their experimentally observed behavior. Most of the studies have been performed with continuous-wave illuminating beams up to a few tens of W/cm2. Up to now few systematic studies have been performed with short duration pulses and high peak intensity.4,5 Pulsed illumination measurements are important because they give us additional information about photorefractive properties and because of its potential for practical applications.
Wave mixing and beam profile control in a photorefractive waveguide
Authors: Yu Wenqian , Królikowski Wiesław , Luther-Davies Barry , Webster Mark , Austin Michael
Published: February 2023

Photorefractive wave mixing in a waveguide geometry has been demonstrated recently in experiments with such materials as LiNbO3,1 or BaTiO3.2 The high photorefractive efficiency of the latter material allowed even the self-phase conjugation process using guided beams to be observed.2 The waveguide geometry often leads to significant improvement of the photorefractive response time due to the high light intensity caused by spatial confinement. It also offers the possibility of performing wave mixing directly in integrated optics devices. Additionally, very promising photorefractive polymers favor the thin film geometry due to the need for electric poling.3
Probe beam wave-guiding induced by spatial dark soliton in photorefractive Bi12TiO20 crystal
Authors: Iturbe Castillo M. D. , Márquez Aguilar P. A. , Sánchez-Mondragón J. J. , Stepanov S. I. , Klein M. B. , Wechsler B. A.
Published: February 2023

Optical waveguides have produced a new wave of interest with realizing the fact that the light can be guided by light. These phenomena occur when an intense (pump) light beam propagates in an optically nonlinear medium, generating stable spatial structures called spatial soliton. Depending on the sign of non-linearity, spatial solitons can be bright or dark. The former one represents an isolate beam profile, and the latter one consists of the absence of radiation immersed in a continuous light background. Generation of dark spatial solitons can be performed by placing an amplitude or phase mask into the incident pump beam in order to produce the adequate initial condition. In particular, a 180° phase jump mask produces an odd number of dark solitons. Joined with the stability of such structures is the fact that the intensity of the beam modifies the medium itself, causing a change in the refractive index according to the intensity profile of the spatial solitons. Then another probe (weak) beam can be sent into the medium and can be guided along the soliton axes.
Intermediate fanning and dependences of fidelity and build-up dynamics on an angle between the pumps for photorefractive double-pc mirror
Authors: Bel'dyugina N. I. , Mamaev A. V. , Shkunov V. V.
Published: February 2023

Double phase conjugate mirror (DPCM)1 being an effective and widely used scheme to conjugate beams of different laser sources is still a puzzle from the viewpoint of a mechanism of its operation in PC mode. In this report we present experimental and theoretical arguments which undoubtedly indicate that an intermediate fanning is responsible for PC mode of DPCM.
Generation of 90 mW CW tunable laser light at 280 nm by frequency doubling
Authors: Nielsen J. S.
Published: February 2023

For use in laser cooling of 24Mg+ ions in the ASTRID storage ring, a CW, tunable, UV laser system producing up to 90 mW of laser light at 280 nm has been built. The system consists of a commercial ring dye laser and an external resonator in which a KDP crystal is placed.
Time and spectral control of the parametric nonlinear mirror by ultrashort pulse train
Authors: Chekhlov O. V. , Kazak N. S. , Pavlenko V. K. , Zaporozhchenko V. A.
Published: February 2023

During recent years we have observed that the outstanding nonlinear phenomena have found nonconventional use in the development of a fast-response modulating device for optical sampling and laser mode-locking.1,2 In this work we have investigated the nonlinear mirror (NLM), based on the frequency mixing processes, that could be applied as the optically driven modulator for laser spectral tuning3 and/or mode-locking.4,5
Wide-angle laser heterodyning
Authors: Vitrishchak Il'ya B.
Published: February 2023

The unique properties of laser heterodyne systems—the possibility of achievement of quantum sensitivity limit even with non-ideal photodetectors, obtaining of information on the phase and frequency spectra of received light, very narrow bandwidth in temporal and spatial domain—define their numerous applications. Instant field-of-view for heterodyne systems is narrow and approximately equal to the diffraction field-of-view for photoreceiver (aerial Siegman theorem). This property can often be referred to as a disadvantage, especially in the survey systems. In this report we analyze the possible ways to overcome this limitation.
Wavelength dispersion of the Kerr effect in optical fibres
Authors: Yao J. , Xu J. , Rogers A. J.
Published: February 2023

It is important to determine the dispersion of the Kerr effect in optical fibres for application to fibre communication and fibre sensors; little information on this effect presently exists in the literature. The Kerr coefficient K, has been found to vary with material, wavelength, and temperature. The classical Havelock's Law1 has the form of K = c(n2 - 1)2/E2nλ where λ is the wavelength, c is a material constant and independent of wavelength, n is the refractive index, and E is the applied electric field. Havelock's law appears adequate for some materials. It has been verified experimentally by several investigators.2,3 In order to measure the very small Kerr coefficient for silica optical fibres, the experimental arrangement in Fig. 1 was used. The Kerr coefficient K = dI0/IπlE2 can be measured by detecting the parameters dI0, the light intensity variation, I, the total light intensity, E, the applied electric field, and l, the length of the fibre.
All-optical modulation and amplification via cascading in lithium niobate waveguides
Authors: Torelli I. , Assanto G. , Trillo S.
Published: February 2023

Cascading of quadratic nonlinearities allows us to obtain large phase shifts for all-optical processing.1−2 The tensorial nature of the second-order susceptibility lends itself to a richer set of interactions than the scalar ones analysed to date, and we propose novel schemes for all-optical modulation and transistor action based on the coherent interaction between two orthogonally polarized fundamental waves and the generated second-harmonic (2ω) in a y-propagating z-cut Lithium Niobate waveguide.
TM nonlinear modes in a liquid crystal optical waveguide
Authors: Abbate G. , Castaldo F. , De Stefano L. , Mormile P. , Santamato E.
Published: February 2023

Liquid Crystals (LCs) are by far extensively studied in integrateci optics because of their exceptional mechanical and optical properties, and a lot of optical devices for guided optics, based on linear and nonlinear effects in these materials, have been proposed.1 Efficient control of the guided light can be obtained, for example, acting on the LC placed in the substrate2,4 or in the core3 of a slab waveguide with an external (electric, mag netic, or optical) field. In this work, instead, we study the self action of an intense optical field propagating in the waveguide core made of a liquid crystal material. Strong planar alignment of the LC molecules is assumed at the walls and only TM modes are considered. (It can be shown that, above a critical threshold of the guided power, such a nonlinear structure cannot support pure TE modes.) Moreover, the waveguide is assumed to be symmetric, so that only even or odd modes are supported.
Characterization of open slab CO2 lasers for slab-array construction
Authors: Lapucci A. , Rossetti F.
Published: February 2023

Recently we proposed a new laser design1 that presents both the properties of large area discharges in one transverse direction and those of laser arrays in the other. In this scheme the different channels can be viewed as slab guides with open side walls letting part of the field be injected into the next neighboring one. When the different channels are locked, the emitted beam consists of coherent strips.2,3 The main problem with this kind of structure is related to the amount of losses necessarily determined in the single channel in order to achieve coherence on the whole array.
Observation of the interaction between a lithotripter shock wave and a simulated kidney stone
Authors: Carnell M. T. , Emmony D. C.
Published: February 2023

Schlieren photography provides an excellent method for the observation of acoustic shock phenomena in water. The shock waves were generated using an electromagnetic acoustic transducer (EMAT) and a focusing lens. The discharge of 81 J through the EMAT device produces acoustic transients with a peak pressure of 20 MPa, a period of 6 µs, and acoustic energy densities in the region of 0.106 mJ/mm2. The ratio of peak-positive-to-peak-negative pressure was approximately 3. The conventional two lens, parallel beam Schlieren system was illuminated by a Q-switched ruby laser giving the system a spatial resolution of 30 µm for shock transients in water. At maximum sensitivity the system was capable of detecting pressure changes of approximately 300 Pa. Located at the focus within the Schlieren observation area was a simulation kidney stone, manufactured from a mixture of plaster and microballoons by HMT GmbH. Figure 1 shows the Schlieren image of the transmitted and reflected components associated with the interaction of a shock wave with the simulation material. The stone is right of centre and the focusing lens surface is just visible on the far left. The insert shows the Schlieren image of the incident shock wave in which the bright components represent the alternating compression and rarefaction cycles of the wave. Shock propagation is from left to right. The transmitted shock wave during its passage through the material has become attenuated to such an extent that only the main compression and rarefaction cycles are seen. Also present within the field is cavitation, its appearance being most marked on the front face of the block.
Organic multiple quantum well: fabrication and optical properties
Authors: Forrest S. R.
Published: February 2023

Summary not available.
Efficient frequency doubling of CVL-pumped Ti:sapphire lasers
Authors: Evans I. J. , Wadsworth W. J. , Webb C. E.
Published: February 2023

The copper vapour laser (CVL) provides an efficient source of high repetition rate laser radiation operating at two wavelengths simultaneously—510.6 nm in the green and 578.2 nm in the yellow. The CVL wavelengths are well matched to the absorption bands of the Ti3+ ion in the sapphire host. We have already shown that both high efficiencies and narrow linewidths can be obtained from CVL-pumped Ti:sapphire laser systems over the range 720-950 nm.1 By frequency-doubling a CVL-pumped Ti:sapphire laser, we have recently demonstrated an efficient source of high repetition rate tunable laser radiation in the blue/ultra-violet region of the spectrum.
Fast manipulation of the gain medium of an infrared free electron laser
Authors: Auerhammer J. M. , Haselhoff E. H. , Knippels G. M. H. , van der Meer A. F. G. , Oepts D. , Weits H. H. , van Amersfoort P. W.
Published: February 2023

A free electron laser is similar to regular lasers in the sense that a light pulse is amplified on multiple passes through an optical cavity. Although the pump and gain processes are completely different, manipulation of the stored field is possible using similar tricks as in regular lasers, for instance phase locking by means of an intracavity interferometer.1,2 In addition, however, a free electron laser has the unique feature that also the properties of the gain medium (a beam of relativistic electrons) can be manipulated on a time scale essentially down to the cavity roundtrip time.