bluuebunny/crossref_metadata_2025 huggingface dataset:
An All Optical Faraday Current Sensor Using Semimagnetic Crystals
Authors: Podoleanu Adrian Gh. , Cucu Radu G. , Jackson David A.
Published: February 2023

We demonstrated a single down lead common-mode rejection scheme for a Faraday current sensor that can eliminate optical noise induced by fibre-link vibration [1]. The configuration was based upon the creation of temporally delayed replicas. One replica was encoded with the Faraday signal and the optical noise, (F+Z), and the other contained the noise component only, Z. By using a pulsed laser diode and suitable optical delays at the probe level and electrical delays at the receiver ground level, the two replicas were combined differentially and time gated to eliminate the noisy signal Z. The probe used a rod made of diamagnetic Schott SF6 glass as the Faraday transducer and the sensitivity was quite low. In addition, the common mode rejection was sensitive to pulse shape alteration in the system as the two replicas were subtracted in their pulse format at the receiver point. We present an improved set-up where the diamagnetic glass is replaced by a semimagnetic Faraday crystal. Cd0.57Mn0.43Te with a much higher Verdet constant [2] to increase the probe sensitivity. A second improvement consists in processing the two replicas up to the DC level (i.e. they are amplified and rectified separately) and only after that subtracting them. A further development is introduced by increasing the delay between the two replicas. Light from the crystal is directed towards a single mode coupler, whose output leads are silvered and have different lengths to implement a differential delay of τ ≈ 10 ns between the pulses reflected back to the single mode coupler inputs. The light from the other coupler input is directed via a fibre optic lead to the ground receiver. Polarization controllers in the two arms maximize the Faraday effect on one arm and minimizes it on the other arm. Then, at the receiver point, the signal is split into two channels where an electrical delay τ ≈ 10 ns is introducd. The two channels are fed into two time gating amplifiers, each passing the input signal to the output during the pulsewidth of the gating signal. The gating signal is supplied by the same generator used to drive the laser and it is suitably delayed to coincide with the signal to be selected. Then the signals (F+Z) and Z are rectified and applied to a differential amplifier. The main focus of the paper is the optical and electronic processing unit, designed to perform the common mode rejection without resorting to high cost optical and electronic RF components. Pulsewidths of 4 ns have been used ensuring good separation of adjacent pulses at 10 ns. which represents a good compromise cost-performance. As a first proof of the improvements, the subtraction of signals ceased to be dependent on the variation of the electrical delay alteration, a problem experienced in the implementation [1].
Influence of material anisotropies on photorefractive gain and speed
Authors: Montemezzani G. , Günter P.
Published: February 2023

The physical and optical properties of inorganic and organic materials with large photorefractive effect are often strongly anisotropic. Three important kind of anisotropies can be identified. First, the magnitude of the electro-optic effect and of the low frequency dielectric constant depend on the direction of the internal space-charge field and, specially in inorganic crystals, is strongly affected by mechanical coupling within the material. Second, charge transport, i.e. carrier mobilities, can differ significantly for different drift directions [1]. Finally, photoexcitation cross-sections can be anisotropic with respect to wave polarization. This affects the magnitude of the photorefractive space-charge fields and can give rise to a significant enhancement of two-wave mixing gain coefficients [2].
A New Efficient Technique for Measurements of Trap Concentration in Photorefractive Materials
Authors: Petrov M.P. , Bryksin V.V. , Petrov V.M. , Karavaev P.M. , Wevering S. , Kratzig E.
Published: February 2023

When a hologram is recorded in a photorefractive material by two beams, one of which is periodically phase modulated (with amplitude Θ and frequency Ω), the output signal in a two-wave mixing configuration contains two temporal harmonics with amplitudes UΩ (at Ω) and U2Ω; (at 2Ω) . The origin of U2ω in the case when the drift mechanism prevails and the diffusion mechanism is negligible is associated with the phase shift Δ between the interference pattern and the holographic grating. The value of Δ is determined by tgΔ = [Illegible] where E is the external field and Eq is the saturation field, E [Illegible] where NA is the trap concentration, e is the electron charge, ε is the dielectric constant, and K is the grating wave vector. It follows from [1] that U2Ω/UΩ = J2 (Θ) [J2 (Θ)]-1 tgΔ, where J. and J2 are Bessel functions. The experimental measurements of the ratio U2ω/Uω allows one to find E[Illegible] and NA. This technique was used to measure E[Illegible] and NA in many samples of [Illegible] and [Illegible]. The values of NA were found to be of the order of 10[Illegible] cm-3 for BSC and of the order of 10[Illegible] cm-3 for BTO, consistent with the available literature data obtained by other technique.
Excited-State Absorption in ZBLAN:Er3+: Implications for a Diode-Pumped 3-µm Fiber Laser
Authors: Pollnau M. , Ghisler Ch. , Lüthy W. , Weber H. P.
Published: February 2023

Erbium-doped fluorozirconate (ZBLAN) fibers are promising candidates for the construction of compact and efficient all-solid-state 3-µm laser sources for surgical applications. Excited-state absorption (ESA) was found to have a major influence on the lasing properties of the erbium 3-µm transition in ZBLAN fibers. An approach has been suggested recently [1], which aims to avoid pump ESA and requires only low pump intensity, thus enabling high-power double-clad diode pumping of the erbium 3-µm fiber laser. However, the values of the relevant ESA cross-sections could not be determined experimentally so far. because the pump excitation is distributed between two metastable levels of erbium in ZBLAN, and ESA transitions from these two levels overlap in the spectral region of interest.
Technique for Characterization of Polarization Mode Dispersion Accumulation Along Optical Fibres
Authors: Sunnerud Henrik , Olsson Bengt-Erik , Andrekson Peter A.
Published: February 2023

When chromatic dispersion in optical fibres no longer limits the data rate of transmission systems, polarization mode dispersion (PMD) may become the major limiting factor. Various techniques exists for measuring the PMD as an average in a fibre link while, to our knowledge, only one method for characterization of distributed PMD has been suggested [1], which is focused on measuring fibre birefringence in short fibres. We propose a novel non-destructive technique for measuring the accumulation of PMD along a fibre link. The idea is to create a map of fixed-analyser spectra [2] along a fibre, from which the accumulated differential group delay (DGD) and the corresponding PMD can be derived.
Measurement of particle shape using polarisation fluctuations of scattered light
Authors: Pitter M C , Hopcraft K I , Bates A P , Jakeman E , Walker J G
Published: February 2023

The shape of particles and their orientations in space are of importance in the manufacture of aerosols, paints and coatings, pharmaceuticals and to sensing and imaging through turbid random media The use of polarised radiation affords a greater flexibility to address these characteristics through the use of light scattering techniques In the case of scattering by many very small particles, polarisation ratios, distributions and correlation functions of scattered polarised light all require additional information to resolve measurement ambiguities. However, we have recently shown [1] that the shape of the probability density of scattered radiation from a single small scatterer provides a means to determine the shape of spheroidal particles uniquely.
Broadband femtosecond stimulated Raman scattering in H2-D2, H2-HD and H2-CH4 gas mixtures
Authors: Krylov V. , Oliikainen O. , Gallus J. , Wild U. , Bespalov V. G. , Staselko D. I. , Rebane A.
Published: February 2023

Stimulated Raman scattering (SRS) in gases is an efficient method of frequency conversion of laser pulses with nano- pico and femtosecond [1] duration in the broad spectral range from UV to near IR. Previously we have shown that H2, D2, HD and CH4 are most appropriate media for transient femtosecond SRS due to large transient gain coefficient, short molecular relaxation time T2 and high optical breakdown threshold. Due to coherent character of Stokes- and anti-Stokes components, it has been suggested to use SRS for producing ultrashort pulses in sub-10-fs duration range [2].
Single Laser Pulse Bending of a Circular Plate: Model & Experiments
Authors: Dovč Marjan , Kosel Franci , Možina Janez
Published: February 2023

The deformation of a moderately thick plate after it is exposed to a single-mode laser pulse is investigated with the single pulse deformation (SPD) model. The problem is known in many laser processing applications such as welding, cutting and metal forming, where pulsed techniques are used and the sample is usually flat. In metals the light is absorbed only at the thin surface layer, which is heated up more than the rest of the plate1. Consequently, thermal expansion decreases along the plate thickness2. In the cooling phase the deformation sinks back into the plate. When during the heating phase the internal Von Mises equivalent stress exceeds the yield stress, the material around the plate center becomes plastic. Therefore, the pressure exerted onto its elastic surroundings drops and the initial outward expansion of the plastic area is less than would be expected. Instead of expanding this region grows thicker. In the cooling phase the plastic matter returns into the elastic state almost immediatelyand there is no time to reshape into its primary form. The upper layers stays shorter and thicker, and hence the plate's center bends away from the top surface.
Mach-Zehnder modulators monolithicaliy integrated with Fabry-Perot laser diodes in GaAs/AlGaAs using impurity-free vacancy disordering
Authors: Helmy A. Saher , Ooi B. S. , Camacho F. , Bryce A. C. , Aitchison J. S. , De La Rue R. M. , Marsh J. H.
Published: February 2023

Direct modulation of laser diodes can reach frequencies as high as 33 GHz1 sacrificing, however, other performance aspects such as operating power, optical loss, linewidth, and chirp. A better approach is to use external interferometric modulators, which can provide lower insertion losses than electroabsorption modulators,2 and also allow the chirp level to be engineered to suit the associated optical link. Although integration is feasible using etch and regrowth techniques to realise the material composition variation required between the laser and the modulator, such techniques have major limitations.3 An alternative, more elegant, solution has become feasible due to recent advances in the process of quantum well intermixing (QWI).
Carbon Nitride Films Synthesis and Deposition by Excimer Laser Ablation of Graphite Targets in Nitrogen Atmosphere
Authors: Acquaviva S. , D’Anna E. , De Giorgi M.L. , Leggieri G. , Luches A. , Martino M. , Perrone A. , Zocco A.
Published: February 2023

The prediction of a covalently bound carbon nitride solid β-C3N4 [1], with characteristics comparable to or even better than those of diamond, stimulated many attempts to synthesize and deposit thin carbon nitride films. In spite of almost a decade of search, this material has not yet been synthesized in stoichiometric phase. Nevertheless, it poses interesting issues about formation processes, C-N bonding states and CNx film properties. Ion/atomic beam assisted depositions are most frequently used. We are obtaining good results by using the simple technique of reactive laser ablation [2].
Gasdynamical studies of laser generated plasmas using a ballistic pendulum
Authors: Kapitan D. , Coutts D. W. , Webb C.E.
Published: February 2023

Gasdynamical studies on plasma plumes generated during pulsed laser ablation of solid targets continue to be of interest to improve the understanding of the adiabatic expansion of the ablated material into a (rarefied) background gas. For example, experimental reports in the field of pulsed laser deposition including Schlieren imaging, time-of-flight spectroscopy and ion probe measurements have elucidated the dynamic behaviour of plasma plume. In this paper an alternative approach will be taken to study the gasdynamical properties of the plasma plume by measuring the recoil impulse transferred onto the solid target using a ballistic pendulum.
Actively and passively Q-switched miniature Nd:YAG ring laser with high average power in single-frequency operation
Authors: Bode M. , Spiekermann S. , Tünnermann A. , Welling H. , Freitag I.
Published: February 2023

Q-switching of solid state lasers is an established technology to obtain high peak powers and pulse widths in the nanosecond regime for applications like laser materials processing, time-resolved metrology or in the field of nonlinear optics. By providing a mean to change the quality (Q) of the laser cavity abruptly and repeatedly from high losses to low losses, the laser is forced to emit subsequent pulses instead of continuous radiation. In combination with diode pumping, very compact and efficient pulsed laser sources can be realized.
Long Wavelength Vertical Cavity Lasers
Authors: Streubel K. , Hammar M.
Published: February 2023

Long-wavelength Vertical Cavity Lasers (VCLs) emitting at 1300 or 1550nm are considered as promising candidates as low-cost light sources in fiber optical communication systems Despite the success of their short-wavelength counterparts, and even the demonstration of well-above room temperature continuous operation of a double-fused VCSEL at 155nm /1/, their final demand on mirror reflectivity (>99.5%), uniform current injection and exact gain-cavity tuning, is even further pronounced in the long wavelength regime. This is mainly due to excessive losses (intervalence band absorption, Auger recombination and diffraction) and a relatively small refractive index difference in the InGaAsP/InP system. To overcome these problems, several generically different designs have been presented and investigated The so far most successful approaches use at least one wafer fusion step to combine an InGaAsP active layer with one or two AlGaAs/GaAs DBRs However, such solutions are rather complex from a processing point of view, not yet demonstrated as full two-inch compatible. A more attractive design in this respect is based on the combination of an InGaAsP/InP bottom DBR and a dielectric top mirror So far such lasers have been limited to low-temperature operation /2/, but significant improvements can still be expected from a better optimized current injection scheme or improved dielectric mirror quality Alternative approaches, e g., based on GaInNAs lattice matched to GaAs as active material may also become of importance.
Spatial Mode Discrimination in a Vertical Cavity Surface Emitting Laser by a Fabry-Perot Etalon
Authors: Leger James R. , Chen Guoqiang , Gopinath Anand
Published: February 2023

Methods to increase the cw power of VCSELs generally require increases in mode area. To maintain single mode operation, a strong mechanism to discriminate against higher-order modes must be incorporated in the optical resonator structure. Spatial filtering methods have been employed in the far field to selectively enhance the modal reflectivity of the fundamental VCSEL mode [1]. However, for large aperture VCSELs, the far field light distribution is usually produced by a lens, making integration of the lens and filter difficult. In this experiment, we use the angular reflectivity properties of a Fabry-Perot to perform spatial filtering in the near field [2], permitting a modal selection mechanism that can be easily integrated into the VCSEL structure.
Far-infrared streak camera
Authors: Rella C. W. , Drabbets M. , Lankhuijzen G. M. , Noordam L. D.
Published: February 2023

The spectral range at which conventional streak camera systems operate is limited by the spectral response of the photocathode used. For most photocathode materials the sensitivity is limited to wavelengths shorter than 1.5 µm. Beyond this wavelength the quantum efficiency of the photocathode becomes negligible. The temporal profile of mid- and far-infrared light pulses can thus not be measured directly using a conventional streak camera.
All-optical pseudorandom bit sequence generator
Authors: Poustie A. J. , Blow K. J. , Manning R. J. , Kelly A. E.
Published: February 2023

The ability to perform all-optical digital information processing is one of the key requirements for future photonic networks. Recently, the use of semiconductor optical amplifier based all-optical interferometric switches [1] has allowed practical demonstrations of advanced functionality to be demonstrated. These have included a bit-serial regenerative optical memory which is capable of long term storage [2] and has the ability to restore the optical logic level [3]. Here we describe a further advance in all-optical digital functionality with a demonstration of an all-optical pseudorandom bit sequence (PRBS) generator. The all-optical PRBS comprises two coupled regenerative memories [2] which act as a time-of-flight shift register for optical pulses. A digital PRBS can be generated by applying the logical XOR function between the output of the register and a tap point and feeding the logical result back into the start of the register [4]. We use two TOAD all-optical switching gates [5] to create the all-optical PRBS architecture. One TOAD is used for the XOR function and the other acts as a wavelength converter and all-optical regenerator. The PRBS output depends on the number of pulses m in the shift register and the tap position n (n<m). At present, the experimental latency is several hundred bits at a IGHz clock rate and so we use multiples of lower length sequences in order to measure the performance of the design. We have experimentally demonstrated a maximal length 231-1 PRBS ({m,n}={713,552} ≡ 23 x {m,n}={31,24}) and also sub-maximal sequences. The figure below shows a digitally sampled part of the maximal 231-1 PRBS. The apparent amplitude modulation of the pulses is an artefact of the relatively low sampling rate (400Msamples/s). We were only able to record short temporal sequences since the repeat period of the PRBS is ~50s.
An active smart pixel with low optical input energy, high contrast and high switching speed
Authors: Welker M. , Knüpfer B. , Oehler Ch. , Geißelbrecht W. , Döhler G.H. , Jung Ch. , Wiedenmann D. , Ebeling K.-J.
Published: February 2023

We report on the characterization of a hybrid smart pixel using a special photoconductive switch [1] as receiver and a vertical cavity surface emitting laser (VCSEL) as transmitter component. Due to its special design, the photoconductive switch provides sufficient gain to operate the VCSEL without any further intermediate electronics. In the on-state the smart pixel exhibits an optical output power of 1.5 mW. The DC switching contrast is in excess of 30 dB. We measured a 3 dB bandwidth of 300 MHz (corresponding to a Bitrate of 600 MBit/s) while still obtaining an optical gain of 2.2. The overall optical switching energy is as low as 795 fJ.
2.8μm emission of Er-doped CaF2 planar waveguides fabricated by molecular beam epitaxy
Authors: Daran E. , Shepherd D.P. , Schweizer T.
Published: February 2023

The wavelength range near 3μm has many applications in medical processes due to an overlap with the absorption spectrum of water. Emission of the Er3+ ion near 2.8μm, which operates on the transition from 4I11/2 to 4I13/2 is especially promising as it can be pumped by either 800nm GaAlAs or 980nm InGaAlAs diodes, paving the way for a compact device with low electrical energy consumption.
Self-pulsation in a Semiconductor Ring Laser
Authors: Taguchi Kozo , Fukushima Kaname , Ishitani Atsuyuki , Ikeda Masahiro
Published: February 2023

Semiconductor ring lasers have many capabilities of realizing new functional devices, such as retiming circuits, logic devices or optical ring gyros. M. Ikeda et al. proposed self-detection method of lasing characteristics for semiconductor ring lasers without branching optical lasing power[1]. The lasing power and the line width as a function of the injection current have been measured with detecting the RF power by the terminal voltage change of a ring LD. In this paper, we demonstrate that semiconductor ring laser operates as Q-switched optical pulse generator. Q-switched lasers are very attractive sources in many applications such as optical communication system.
Novel Measurement Scheme for Injection Locking Experiments with Semiconductor Lasers
Authors: Troger J. , Nicati P.-A. , Thévenaz L. , Robert Ph. A.
Published: February 2023

Injection locking experiments with semiconductor lasers started in the early eighties. A lot of work was performed since then mainly dealing with locking range and stability, noise, modulation, chirp and linewidth reduction, sidemode injection locking, optical frequency conversion and micro-wave signal generation. However, there is a lack of quantitative comparison between experimental data and theory. The main reason for this relies on the fact that the experimental set-ups used in most former studies are based on the free-space propagation of light. This causes difficulties in controlling the exact amount of light injected into the slave laser cavity, because the spatial overlap between the optical mode in free-space and the slave laser waveguide is unknown. The experimental set-up presented in this paper allows to overcome this problem. The light generated by the master laser travels through an optical fibre before being injected into the cavity of the slave laser. Using the reciprocity principle, it is possible to control accurately the absolute light power injected from the master laser into the cavity of the slave laser once the power coupling coefficient between the slave waveguide mode and the fibre mode is determined. In addition, the polarisation can be fully controlled despite the birefringence of the optical fibre.
A multimode model for the dynamics of a semiconductor laser with optical feedback
Authors: Kent A.J. , Huyet G. , Hegarty S. , Porta P. , McInerney J.G. , White J.K. , Moloney J.V.
Published: February 2023

Optical feedback has been applied to semiconductor lasers to produce single mode line narrowed output. However it can sometimes produce startlingly rich dynamics and has sparked great interest and enthusiasm among experimentalists and theoreticians alike. From a fundamental point of the dynamics is complicated and intriguing. From a technological point of view it is extremely important to understand if the feedback can be used to control the laser and. if not, to know to what extent semiconductor lasers should be isolated. It may also form the basis for novel remote sensing schemes.
Suppression of a stimulated Raman sideband under dual­wavelength pumping in a single-mode fiber
Authors: Sylvestre T. , Maillotte H. , Lantz E.
Published: February 2023

Although stimulated Raman scattering (SRS) is a frequency downshifted process that can turn optical fibers into several devices, it can also be detrimental to optical transmissions because of Raman-induced crosstalk in wavelength-division multiplexing (WDM), cross-phase modulation or soliton self-frequency shift processes1. It thus limit the power level used in fiber communications links. The stimulated Raman threshold can be increased via parametric suppression1, where the coupling between growing phase-matched four-wave mixing (FWM) sidebands inhibits the growth of Raman Stokes scattering. This situation is efficient if the parametric frequency shift does not lie within the Raman gain bandwidth. Recently, the orthogonal component of the Raman gain has been used for SRS suppression in anyone of the axes of a birefringent fiber, under dual­frequency cross-polarization pumping2. In the present work, we used the antisymetry of the Raman susceptibility for demonstrating the SRS suppression under a single-polarization dual-frequency pump scheme, with no appearance of phase-matched FWM sidebands.
Polarization Domain Wall Solitons with Counterpropagating Laser Beams
Authors: Pitois S. , Millot G. , Wabnitz S.
Published: February 2023

The coupling between two intense laser beams in a nonlinear dielectric leads to a host of physical effects. In particular, the interaction between the polarization states of two counterpropagating ligth beams may generate polarization domain wall (PDW7) solitons [1]. We present what we believe is the first experimental observation of PDW7 soliton formation in a nonlinear dielectric medium.
Spectroscopy of transient photoconductivity in diamond materials with optical parametric oscillator: enhancement of photosensitivity by UV radiation
Authors: Klimentov S. M. , Garnov S. V. , Pimenov S. M. , Konov V. I. , Gloor S. , Lüthy W. , Weber H. P.
Published: February 2023

Application of polycrystalline diamond films in laser optics and electronics calls for detailed knowledge on mechanisms of their photoexcitation. As was recently reported, an exposure of the chemical vapour deposited (CVD) diamond films to UV radiation can enhance conductivity and photosensitivity in wide range of spectrum1. To measure photoexcitation spectra in CVD and natural diamond and to reveal spectral details of the UV enhancement we combined registration of transient photoconductivity (TPC) with OPO as a source of short (~1 ns) pulses of intense radiation tuneable in the range 430-690 nm. TPC is a new “electrode-tree” technique, allowing to study mechanisms of absorption, behaviour of free electrons and holes and recombination with sub-nanosecond resolution time2. The OPO applied was temperature tuneable travelling wave double pass oscillator-amplifier (ADP crystal), pumped by fourth harmonics of radiation of single frequency YAG:Nd laser. The samples were a high quality gem stone and a free standing diamond film grown by microwave plasma deposition technique.
Two-Wave Coupling Measurement of Grating Phases and Self-Diffraction Oscillations in a Photopolymer Film
Authors: Kwak Chong Hoon , Kyong Chon Su , Sung Gee Young , Choe Ok Shik
Published: February 2023

Several techniques for determination of grating phase shifts relative to intensity grating have been developed by introducing artificial phase mismatch which includes by moving the nonlinear material, by phase shifting one of the two writing beams or by applying external electric fields.(1) In this work, we performed two kinds of experiment for two-wave energy couplings in a photopolymer film: (i) measurement of grating phase shifts of phase grating (PG) and absorption gratings (AG) by translation of the material along the grating wave vector K, (ii) experimental observation of quasi-periodic dynamic self-diffraction oscillations without introducing artificial phase mismatch.
Intensity dependence of the sensitivity of a photorefractive polymer composite and improvements in the electro-optic dye constituent
Authors: Rahn M. D. , Wade F. A. , West K. S. , Shakos J. D. , West D. P. , King T. A. , Blackburn R. D.
Published: February 2023

Polymer photorefractive devices are formed by sandwiching an electro-optic dye/photoconducting polymer composite between two indium tin oxide coated glass substrates Holographic information may be written in the material using two coherent optical beams. Device diffraction efficiencies of 60 %, holographic growth times of a few hundred milliseconds and two beam coupling gain coefficient of greater than 200 cm-1 have been reported[1]. High gain and low manufacturing costs of polymer devices are clear advantages over photorefractive crystals, although typical holographic grating risetimes of a few hundred milliseconds are restrictive.
Role of Diffraction in Selection of Wave Phase-Conjugated to Input Speckled Beam in Resonator with Holographic Mirror.
Authors: Yarovoy V. V.
Published: February 2023

Optical oscillator with holographic mirror formed by external signal wave (fig. 1) is considered to be one of the prospect and effective PC-corrector being used in different laser systems. When one needs to reconstruct information about object wave distorted by transmission function of some random transporting medium (for instance, of multimode fiber) one has to deal with the hologram recorded by two waves both of them being speckled ones. In this case, the traditional holography (Gabor’s holography) based on the principle of “supporting"(when one of the two writing waves is considered to be plane wave against the background of other, I1 E3 =const E3) turns out to be practically unacceptable.
Polychrome Correction for Telescope Lens Distortions using Optically Addressed Liquid Crystal Spatial Light Modulator
Authors: Vasil’ev M.V. , Berenberg V. A. , Leshchev A. A. , Venediktov V. Yu.
Published: February 2023

Holographic correction for telescope lens distortions was first proposed and realised yet in 70-es1; in this and more recent experiments2 the holograms were recorded in the static media, providing thus correction only for static distortions. The prospective scheme, which can be used for real-time dynamic correction in wide spectral range, uses thin (plain) dynamic hologram record in the optically addressed liquid crystal spatial light modulators (OA LC SLM). In the experiment we have evaluated wide spectral band imaging by model telescope with the distorted primary lens of the standard test object, irradiated by the tungsten lamp radiation Dynamic hologram was recorded by pulsed radiation at 0.54 μm in OA LC SLM with polymer photoconductor and nematic LC layer. Auxiliary static holographic grating compensated for the dynamic corrector chromatism. In the Figure: (a) - image by non-corrected telescope with distorted by etched glass (extra divergence 6x10-3 rad) primary lens, (b) - corrected image, (c). (d) and (e) - central zone of corrected images, recorded under one and the same experiment conditions by radiation in the band 0.53 ± 0.4 μm - (c), 0.63 ± 0.4 μm - (d, one can see image deterioration due to incomplete compensation at the shifted wavelength) and by white light (e, interim quality between cases c and d).
Characteristics of Nd:YAG laser welding of dissimilar steels with in-line process heating
Authors: Watson Ian A. , Ng Eng S. , Chia Poh S.
Published: February 2023

Joining dissimilar metals with normal welding methods poses interesting and difficult metallurgical problems [1]. The rapid solidification rate associated with laser welding results in non-equilibrium structures due to incomplete mixing in the fusion zone. An experimental study was undertaken to assess the weldabilty of dissimilar metals, mild steel and stainless steel, with pre-heating and post-heating of the weld, utilising Lumonic’s MS830 Nd:YAG pulsed laser, operating at 1.06 µm with a constant power of 285 W with an argon shielding gas pressure of 5x104 Pa. The in-line process heat treatment was achieved with a fibre optic beam delivery system.
Excitation of Whispering Gallery Modes in Fibres by Fibres
Authors: Birks T. A. , Knight J. C.
Published: February 2023

We have recently reported the use of a narrow single-mode fibre taper to excite whispering gallery modes (WGMs) in fused silica microspheres[1]. Here we demonstrate the similar excitation of WGMs in dielectric cylinders. The dielectric cylinder is itself a tapered fibre, made by stretching the fibre in a flame to give a filament of predictable diameter. The two tapers are positioned at right angles and in contact. The transmission spectrum of the "sensor" taper (measured using a tunable diode laser) has dips at wavelengths where light is coupled from its guided mode to a WGM in the "target" taper.
Kerr nonlinearity and nonreeiprocity in a ring laser cavity
Authors: Bosco C. A. C. , Acioli L. H.
Published: February 2023

The nonreciprocal effect introduced by the gain media in a Kerr-lens-modelocked laser is considered. For real nonlinear optical susceptibilities in media without gain or losses phase conjugation is reciprocal[1], the same happening in a cavity where gain is neglected. Once gain is considered, the position of the laser crystal may discriminate between the clockwise and anticlockwise beams through the self-focusing effect, similar to what happens in a nonlinear amplifying loop mirror (NALM). In the present analysis this assymmetry is attributed to the gain dependence on the position z within the laser crystal, due to pump beam depletion. The laser beam that propagates in the same direction as the pump beam acquires a larger nonlinear phase shift, compared to the counterpropagating beam, and therefore suffers a greater self-focusing effect.
Fabrication of Complex integrated Waveguide filters using Electron Beam Lithography
Authors: Millar P , Liu X. , De La Rue R. , Aitchison J.S.
Published: February 2023

Integrated waveguide filters have recently been used in many optical processing applications including the filtering[1] multiplexing[2] and switching[3] of optical signals. In particular chirped grating have been for dispersion compensation in optical fiber systems[4] and apodization is commonly used to suppress the production of sidelobes in the transmission characteristics of grating filters. It is envisaged that in the future telecommunications and optical computing networks will require novel and complex grating structures for the processing and selective switching applications in multi-channel systems. Therefore, a simple and reliable method for the production of grating filters, where the filter charcteristics can be easily tailored is desired. In this letter we describe a single step, electron beam based approach, where the grating and waveguide are defined simultaneously and the grating characteristics arc well controlled.
Low temperature wafer direct bonding between GaInAsP etch stop layer and Gd3Ga5O12
Authors: Yokoi Hideki , Mizumoto Tetsuya
Published: February 2023

Wafer direct bonding is an attractive technique for the integration of different materials without any adhesives. The authors have applied this technique to bonding of a III-V compound semiconductor and a garnet crystal for the aim of integrating a laser diode and an optical isolator. In a previous study, we demonstrated the bonding between InP and several kinds of garnets [1], the latter of which are essential to an optical isolator. Figure 1 shows a laser diode integrated with an optical isolator by wafer direct bonding. A GaInAsP etch stop layer of the laser diode is prepared for vertical alignment between an active layer of the laser diode and a guiding layer of the optical isolator. The vertical alignment can be achieved by adjusting the thickness of cladding layers. The lateral alignment of a waveguide with the laser stripe can be accomplished by conventional lithography and etching techniques. In this paper, we report the direct bonding between GaInAsP and Gd3Ga5O12 (GGG). GGG is used as a substrate for epitaxial growth of magnetic garnets.
Femtosecond-Pulse Laser Ablation of Monocrystalline and Dental Hydroxyapatite
Authors: Krüger Jörg , Kautek Wolfgang , Newesely Heinrich
Published: February 2023

Lasers as potentially practical dental drills still exhibit the problem of thermal side effects This is especially true for Ho:YAG, Er:YAG, and Nd:YLF lasers, both free running and Q-switched, which are very common in medical applications. They yield cratered and rough surfaces with deep cracks due to sudden humidity explosion and micro plasma absorption [1] because infrared radiation couples into the water content of enamel and dentine (4 and 10 %, respectively). Even picosecond-pulse Nd:YLF lasers still cause considerable thermal and mechanical destruction of enamel [2]. Excimer lasers exhibit much less thermal problems but involve the general risk of in-vivo UV radiation application [3,4].
0.5mJ pulses from a single transverse-mode Q-switched erbium fibre laser
Authors: Offerhaus H.L. , Broderick N.G.R. , Richardson D.J. , Sammut R.A. , Capten J. , Dong L.
Published: February 2023

Q-switched fibre lasers offer a simple and robust means for the generation of high energy, nanosecond pulses at eye safe wavelengths around 1550nm suitable for a number of industrial, sensing and nonlinear optics applications. Unfortunately, Q-switched fibre lasers based on conventional erbium doped fibre designs are limited to <10 µJ pulse energies by rapid energy loss in the form of amplified spontaneous emission during the gain recovery stage due to the high gain-efficiency of the fibres. Recently we showed that considerably higher pulse energies (180 µJ) can be achieved simply by increasing the mode field diameter (MFD) of the fibre and thereby compromising the gain efficiency of the system[1]. The increased MFD also improves the nonlinear and power handling characteristics of the fibre.
An Optoelectronic Sorter System
Authors: Gouriay James , Yang Tsung-Yi , Dines Julian A.B. , Forbes Mark G. , Waddie Andrew J. , Walker Andrew C. , Vass David G. , Underwood Ian , Stanley Colin R. , Sibbett Wilson
Published: February 2023

The integration of 2-D optoelectronic interfaces with silicon chips, employing what is known as smart-pixel technology, can overcome many of the foreseen limitations of conventional interconnects [1]. The solution is to provide free-space optical interconnects operating at the silicon on-chip clock-rate and with the numbers required to yield the necessary aggregate bandwidth. To investigate the application of this approach to parallel information processing we have been building an optoelectronic data sorting machine as a system demonstrator. The architecture of the optoelectronic sorter and the design of the components was described previously [2].
Ex-vivo laser-induced fluorescence measurements based on double wavelength laser excitation of peripheral vascular tissues
Authors: Filippidis G. , Zacharakis G. , Katsamouris A. , Giannoukas A. , Papazoglou Theodore G.
Published: February 2023

Laser-induced auto-fluorescence spectra were recorded during the exposure of peripheral vascular tissue to both Helium-Cadmium and Argon ion radiation. Femoral, flank and ham artery samples from by-pass operations were obtained in an unfixed state, within half-hour after the excision. Following gross inspection the specimens were classified as of various degrees of atherosclerosis (fibrous plaque, calcified plaque). In some specimens there was both calcified and fibrous plaque.
Passive Mode-locked Operation of Large Mode Area fibre lasers
Authors: Broderick N. G. R. , Offerhaus H. L. , Richardson D. J. , Sammut R. A. , Caplen J. , Dong L.
Published: February 2023

Recently much work on fibre lasers has concentrated on improving the maximum output energy and peak powers available from such systems. An important recent advance in this area has been the development of single transverse-mode, large mode area (LMA-) doped fibre1. The LMA gives increased energy storage reduces the impact of optical nonlinearities and improves the power handling capabilities of the fibre. We have developed LMA fibre designs allowing robust, single transverse-mode laser operation with fibre Mode Field Diameters (MFDs) in excess of 30 μm, i.e around 5 times larger than conventional doped fibre designs Q-switch fibre lasers based on this fibre have yielded pulse energies in excess of 0.5 mJ. Here we present the first demonstration of the use of such fibre in a passively mode-locked soliton laser. Subpicosecond, 1 nJ soliton pulses are obtained representing more than an order of magnitude increase in pulse energy relative to conventional soliton lasers.
Stable picosecond pulse generation at 1.3 μm in a Pr3+-doped all-fiber laser actively mode-locked using a novel fiber-optic phase modulator
Authors: Nielsen T. G. , Hodel W. , Weber H. P. , Costantini D. M. , Iocco A. , Ky N H. , Limberger H. G. , Salathé R. P. , Fox G.
Published: February 2023

Rare-earth doped fibers are ideal candidates for the realization of simple, compact sources of ultrashort pulses. Considerable effort has been devoted to obtain short pulse generation in Er3+-doped fiber lasers at 1.55 μm. In contrast, little work has been done on Pr3+-doped fiber lasers emitting in the important 1.3 μm region where there is still a lack of compact, tunable short pulse sources. In this work we report on a all-fiber laser incorporating a Pr3+-doped active fiber, fiber Bragg gratings (FBG’s) as cavity mirrors, and a novel piezoelectric fiber-optic phase modulator (PFOM) for active mode-locking [1]. The experimental set-up is schematically shown in the following Figure.
Gain Spectroscopy on InGaN/GaN Quantum Well Laser Diodes
Authors: Kuball M. , Song Y.-K. , Nurmikko A.V. , Bulman G.E. , Doverspike K. , Sheppard S.T. , Weeks T.W. , Leonard M. , Kong H.S. , Dieringer H. , Edmond J.
Published: February 2023

In spite of advances that have led to the demonstration of a 1000 hour cw blue InGaN QW diode laser, as well of the demonstration of cw operation on a SiC substrate [1], major unanswered questions exist about the physics of optical gain in this disordered QW system, given the large departure of InGaN from a random alloy in terms of microscopic scale In-compositional fluctuations. We have reported on gain spectra obtained on InGaN/GaN pn-junction heterostructures [2]. Useful information has been acquired but spectroscopic details were incomplete.
Mid Infrared Sensors Using Periodically Poled LiNbO3 for Trace Gas Detection
Authors: Tittel Frank K. , Lancaster David G , Richter Dirk , Curl Robert F.
Published: February 2023

In recent years there has been an increasing interest in the detection and precise measurements of environmentally important atmospheric trace gases. Applications that require trace gas measurements include industrial, urban and rural emissions monitoring, air quality in confined environments, medical applications, atmospheric chemistry, chemical analysis and process control.
Optical Imaging and Analysis of Speckle Patterns from Escherichia coli in Disinfectant solution
Authors: Yeo C.B. Allen , Watson Ian A. , Wong James W. M. , Stewart-Tull Duncan E S
Published: February 2023

Analysis of speckle patterns [1], the phenomenon caused by interference between light scattered from an object, provides an inexpensive and real time method to assess the state of biological systems with, for example, applications in medicine.
YAG:Nd Scanning Laser System with Phase Conjugation and Master-Oscillator with PLZT-Based Intracavity Spatial-Time Light Modulator
Authors: Alekseev V.N. , Kotylev V.N. , Liber V.I. , Starikov A.D.
Published: February 2023

The feasibility of accurate control over direction of high power beam of a laser amplifier with a help of a signal generated by a low-power master-oscillator with an intracavity light-controlled spatial-time light modulator (STLM) of the PROM type was demonstrated in paper [1]. The PROM type modulator has a low optical strength (~0, 1 J / cm2) in respect to single-pulse radiation and a large period of reversal (~0, 1 s).
Noise in Cavities with Multi-Valued Petermann Factor
Authors: Dunlop A. M. , Firth W. J. , Wright E. M.
Published: February 2023

It is usually assumed that the Petermann K-factor [1] is a cavity property, independent of position z around the cavity. We show that K is not invariant, and consider the implications for laser noise. K arises for optical systems with non-Hermitian modes.
Diode pumped Q-switched Y3Al5O13: Yb-Ho laser
Authors: Nikitichev A.A. , Kuchma I.G. , Levoshkin A.V. , Petrov A.A.
Published: February 2023

The crystal YAG: Yb-Ho was proposed in [1] as the prospective medium for the diode pumped laser, emitting at 2 µm. Strong and wide absorption band of Yb ions, high quantum efficiency of sensibilization at low concentration of the activator and long storage time promise significant decrease of required diode pumping power.
Spectral Analysis of the RF Excited Slab-Waveguide CO2 Lasers with Unstable Resonators
Authors: Plinski E. F. , Abramski K. M.
Published: February 2023

The evolution of the radiation inside the high volume lasers with unstable resonators is quite different compare to the classic Gaussian resonators with standing waves. The spectral structure formed in unstable resonators is not clear. To recognise the spectral frequency components of the output radiation from unstable resonators we built the system for the heterodyne analysis shown in Fig. 1. It enables to detect the self-beat frequencies of modes in the laser output (so called homodyne detection), or heterodyne signals when the tunable single-mode laser is used as a reference to obtain the beat signal (heterodyne detection) [1].
Spectral characteristics of microlaser with waveguide grating mirror
Authors: Lyndin N. M. , Sychugov V. A. , Nurligareev J. H. , Usievich B. A. , Zvonkov B. N. , Zvonkov N. B.
Published: February 2023

The feasibility of waveguide grating mirror usage for narrow wavelength generation and laser tuning was repeatedly demonstrated [1]. Waveguide grating mirror could provide wavelength stabilisation and transverse coherence improvement in semiconductor lasers with wide active region. However, to our knowledge, there is only one publication concerning the utilisation of waveguide grating mirror for the wide active region semiconductor lasers [2]. It is known that waveguide grating mirror efficiently works under normal incidence and this is a great advantage in designing of compact semiconductor laser chip.
Diode-pumped, external-cavity GaAs/AlGaAs surface emitting laser
Authors: Holm M. A. , Cusumano P. , Bums D. , Dawson M. D. , Ferguson A. I.
Published: February 2023

Surface emitting lasers with high output power in a single transverse mode have much potential for applications in optical communications, laser printing and optical data storage. However, single transverse mode VCSEL’s have been limited to 1-5mW and although large aperture VCSEL’s can provide high power they are highly multimode. Optically pumped external-cavity surface emitting lasers1,2 can overcome this limitation because the active region is defined by the shape of the pumping beam which can be matched by the external cavity mode to promote oscillation in a single transverse mode. Furthermore, by operating in an external cavity, various optical elements can be introduced to control the nature of the laser output, e.g. stable, tunable, single frequency- or mode-locked-operation. In this paper we report the initial development and characterisation of diode-pumped, external-cavity GaAs/AlGaAs surface emitting lasers.
A Study of Semiconductor Lasers/Amplifiers with Multiple Quantum Wells of Different Widths
Authors: Lin Ching-Fuh , Lee Bor-Lin
Published: February 2023

It is well known that semiconductor lasers fabricated on the quantum-well structure has much better performance than those fabricated on the heterostructure. Multiple quantum wells are usually used because a higher differential gain coefficient can be obtained by increasing the well number [1]. Conventional multiple quantum wells for the semiconductor lasers have the same width. This wok reports that multiple quantum wells of different widths could lead to semiconductor lasers/amplifiers with very different characteristics.