bluuebunny/crossref_metadata_2025 huggingface dataset:
Up-conversion in YLF:Yb,Tm Laser Crystals
Authors: Tkachuk A.M. , Razumova I.K. , Joubert M.-F. , Moncorge R.
Published: February 2023

The importance of development of the visible lasers emitting in the green-blue spectral range under the laser-diode pumping enforces search for the new and optimization of the known active media for lasers pumped via up-conversion schemes. The YLF:Tm crystals are well-known active media for lasing on a number of lines over a wide spectral range from 0.450 to 2.35 μm upon selective laser, laser diode, and flash lamp pumpings, including up-conversion and ‘'avalanche” excitation mechanisms.
The Up-Conversion Processes Efficiency in Diode Pumped Nd:GdLiF4
Authors: Courrol L.C. , Maldonado E. P. , Gomes L. , Vieira N. D. , Ranieri I. M.
Published: February 2023

Intense yellow and green fluorescences are usually observed during high-power diode lasers pumping at a variety of Nd laser media In the GdLiF4:Nd crystals, these anti-Stokes fluorescences resulted mainly from the excited-state absorption of pumping radiation (ESAP) or the energy-transfer up-conversion (ETU) mechanisms.
Organic Nonlinear Crystals—New Stimulated Raman Scattering Materials
Authors: Khulugurov V.M. , Kidyarov B.I. , Oleynikov E. A.
Published: February 2023

We represent the results of a complex optical, lasers, and spectroscopic studies of organic nonlinear crystals: the lithium formate monohydrate -LiCOOH*H2O (LFM), the urea - CO(NH2)2, the dimethylurea - CO(NHCH3)2, the KLiH4C4O6 and the potassium malate acid - KH5C4O5. These crystals thanks to nonlinear properties and high optical durability widely used as a generators of harmonics and as optical parametric oscillators (OPO).From the one hand the study of SRS these crystals is vary impotent task because as known the principal reason which limited the OPO efficiency is SRS, from the other hand the SRS presented independent interest for generation of the new laser frequencyes.
Flashlamp-pumped Nd:KGW Laser at 1.06 and 135 μm in free-running and Q-switched mode. Results in MOPA configuration.
Authors: Musset O. , Boquillon J.P.
Published: February 2023

Neodimium-doped Potassium-Gadolinium Tungstate crystal KGd(W04)2 or Nd:KGW is a crystal whose structure allows high Nd doping (3 to 8%) without detrimental concentration quenching. In this way it can compete with Nd:YAG in terms of optical gain, despite a poorer thermal conductivity. We present here the results obtained at repetition rates up to 60 Hz. We tested several Nd:KGW rods from two different furnishers, with the same dimensions ( 6.35 x 76 mm) and different Nd dopant levels (from 2.8 to 8 at.%). The end faces were either flat/flat, parallel and AR-coated at 1.06 μm for the 1.06 μm emission or tilted (1°) and AR-coated for 1.06 and 1.35 μm for the 1.35 μm emission?
Luminescence of Flux Grown Ho:YAl3(BO3)4 and PrAl3(BO3)4 Crystals
Authors: Koporulina E. V. , Leonyuk N.I. , Bray K.L. , Hansen D.
Published: February 2023

Borate crystals with general formula RAl3(BO3)4 (R = Y, La-Lu) possess good thermal and chemical stability and can be considered as polyfunctional materials with device potential due to the possibility of wide isomorphous substitutions. Of this borate family, the RExY1-xAl3(BO3)4 crystals are of interest for luminescence applications because they exhibit very low concentration quenching as the rare earth concentration is increased [1,2]. This means that it is potentially possible to achieve stronger luminescence and lower lasing thresholds in this family of crystals with high rare earth concentration. The authors of this work have studied the growth conditions, contents and spectroscopical characteristics of RExY1-xAl3(BO3)4 (RE=Ho) and PrAl3(BO3)4.
Pr:LaSc3(BO3)4 - a new active medium for lasers radiating in the vicinity of 0.647 μm
Authors: Kuzmin O.V. , Kutovoi S.A. , Nesynov E.K. , Panyutin V.L. , Perfilin A.A. , Khait V.L.
Published: February 2023

The paper presents the results of preliminary investigations of spectral-luminescent properties of Pr:LaSc3(BO3)4 (Pr:LSB) crystal. Pr:LSB single crystals with different Pr concentrations were grown by Czochralski technique in iridium crucibles.
Characterisation of LiNbO3:Er/Yb Waveguides
Authors: Camelar E. , Muñoz J. A , Nevado R. , Pernas P. , Sanz J.A. , Lifante G. , Cussó F. , Jaque F
Published: February 2023

Among the optoelectronic devices developed based in rare-earth doped LiNbO3 crystals, the Erbium doped LiNbO3 laser has shown excellent performances [1] becoming the starting point of advanced integrated devices. A limitation in its performances arises from the relatively low absorption cross section in the laser diodes emission range, which limits the pump efficiency. One possible way of improvement, which has been succesfully implemented in other materials, consists on the use of Yb as codopant. Ytterbium not only has a high absorption cross section in the InGaAs emission range but it has also a broad absorption band that offers the possibility of excitation tunning in the 875-1000 nm wavelength region. The great overlap between ytterbium emission and erbium absorption bands allows efficient energy transfer from Yb3+ to Er3+.
The Growth and Characterisation of Stoichiometric LiNbO3 Crystals for Second Harmonic Generation of 1.06 µm Radiation
Authors: Finnan C. , Jiang Q. , Han T. P. J. , Gallagher H. G.
Published: February 2023

Crystals of congruent LiNbO3 are prepared by the Czochralski technique from Li2O deficient melts and contain up to 5% intrinsic defects. As a result, congruent LiNbO3 is susceptible to optical damage when used for second harmonic generation (SHG) of the 1.06 µm output of a Nd:YAG laser. On the other hand, crystals grown by the same technique from non-congruent melts exhibit significant compositional variations along their length due to segregation effects, with a corresponding deleterious effect on many physical properties such as Curie point, birefringence, phase matching temperature and absorption edge.
Nd:YAG Laser with Stimulated Brillouin and Raman Scattering Pulse Compression
Authors: Gorbunov V.A. , Serebryakov V.A. , Startsev V.R. , v’assil'yev A.F.
Published: February 2023

The design of pulse compressors based on stimulated Brillouin scattering for the generation of subnanosecond pulses at energies approaching the Joule level is an active field of research. Backward stimulated Raman scattering allows for further compression of the pulse up to tens picosecond with production of light at new wavelengths. We present a design of laser with a multiple-cell stimulated scattering pulse compression which can output up to 500mJ per pulse with a 7-ns to 50-ps pulse duration and a 5-Hz pulse repetition rate.
Photorefractivity of indium oxide (InOx) using 193nm excimer laser radiation
Authors: Pissadakis S. , Mailis S. , Reekie L. , Eason R. W. , Vainos N. A. , Moschovis K. , Kiriakidis G.
Published: February 2023

Indium Oxide (InOx) is being extensively used in microelectronic technology due to its important optical and electrical properties. Dymanic photorefractive behaviour of InOx exposed in the near UV region (325nm) at low intensity (~0.25W/cm2) has been demonstrated for films grown by DC magnetron sputtering [1] and Pulsed Laser Deposition [2].
Laser Synthesis of Nanocomposite Cu:Al2O3 thin Films for Nonlinear Optical Switching
Authors: Ballesteros J.M. , Afonso C.N. , Solis J , Serna R
Published: February 2023

Metal nanocrystals embedded in dielectric matrices have been the subject of intense research during the last few years as promising candidates for all-optical switching applications. However, the lack of suitable techniques to produce these materials in waveguide configuration has hindered the use of nanocomposites in technological applications. Pulsed laser deposition (PLD) is a recently developed thin film technique that offers a new way to obtain and control the size and shape of the nanocrystals, thus introducing new possibilities to engineer the nonlinear optical parameters of the material. This work reports on the production of Cu nanocrystals embedded in amorphous Al2O3 matrix with a large nonlinear refractive index and a significantly reduced nonlinear absorption. The influence of the metal content and the measuring conditions on the nonlinear response of the nanocomposite films has been also analysed.
Subpicosecond Carrier Relaxation Dynamics and Defect Formation in Wide-Band-Gap Materials
Authors: Wittmann M. , Wick M.T. , Korn G. , Ringling J. , Matthias E.
Published: February 2023

Alkaline-earth fluorides are widely used in optical transmission components in the deep UV as well as for optical coatings because of their wide-band-gap, low refractive indices and hardness. One essential drawback of these materials is the formation of defects (color centers e. g.) during intense irradiation. This limits the lifetime of such optical elements for high power propagation in the UV and reduces the transmission of ultrashort laserpulses nonlinearly. Details of this process, in particular the dynamics during the early stages (formation of self-trappped excitons STE [1]) are therefor of interest.
Diamond Optics for CO2 Lasers
Authors: Wheatley David , Brierley Crofton
Published: February 2023

The properties of diamond, in particular its very high thermal conductivity, give it enormous potential as a material for laser optics. In the case of CO2 lasers, the standard material ZnSe is a poor conductor and can demonstrate strong thermal lensing at high power densities, often requiring deliberate convective cooling. This paper describes the results of work undertaken to produce and characterize diamond optics suitable for CO2 lasers.
InSb-On-Sapphire Characterization, Infrared and Super High Frequency Responsivity at 300 K
Authors: Padalko A.G. , Shevchenko V. Ya. , Pashkova O.N. , Totrova G.A. , Steblevski A.V.
Published: February 2023

Producing of the emission detectors needs full information about properties of starting material.
Optical system of page organized optical storage device
Authors: Lőrincz E. , Erdei G. , Kalló P. , Richter P. I. , Szarvas G. , Ujhelyi F.
Published: February 2023

A new page organized optical storage device has been developed and functionally tested. The device consists of fields processed parallel with 256 × 256 bits and uses blue laser light for writing and red light for reading binary data when using a polyester recording layer1. A micromirror device serves the purpose of parallel light modulation and an appropriate CCD array is used for parallel data processing.
Efficient Bragg Gratings in Single Mode Planar Waveguide of Chalcogenide Glasses
Authors: Saliminia Ali , Villeneuve Alain , Galstyan Tigran V. , Larochelle Sophie , Richardson Kathleen
Published: February 2023

Chalcogenide glasses (ChG) have been shown to be very promising for application in integrated guided wave devices and infrared telecommunication systems. High optical transparency in the near and far infrared region as well as large optical nonlinearity are two important and attractive properties for using these materials in linear and nonlinear integrated optical elements. It has also been found that the chalcogenide glasses are photosensitive to near band gap illumination (Eg= 2.35 eV). Thin films of ChG exposed to near band gap light have exhibited photostructural changes both in the volume (photodarkening, refractive index changes), and in the surface (photoexpansion, densification). On the other hand, the photoexpansion induces a surface deformation which can also change the optical properties of the material. Both of these effects contribute to increasing the refractive index of ChG allowing us to pattern different photoinduced guided wave structures in ChG thin films. In particular, we present here for the first time to our knowledge, the fabrication of stable and efficient Bragg gratings in single mode As2S3 ChG planar waveguides with near band gap illumination. These gratings can be used to act as wavelength selective components in WDM optical circuits.
Wavelength shifting of optical pulses in a polydiacetylene waveguide
Authors: Banfi G.P. , Fortusini D. , Grando D. , Palchetti L. , Sottini S.
Published: February 2023

We report on wavelength shifting in a polydiacetylene -poly(3-BCMU)- planar waveguide. The effect, of relevance in the manipulation of optical signals, is obtained through nearly-degenerate frequency mixing (NDFM) and is based on the nonresonarit third order nonlinearity of the polymer. Starting from a pulse s at frequency ω
s
, the generation of the frequency-shifted pulse f at ω
f
and the simultaneous amplification of s occur at the expenses of the pump p according to the relation ω
p
+ ω
p
= ω
s
+ ω
f
. We define as the “conversion efficiency” η the ratio of the energy of pulse f at the output to s at the input.
Response of TOADs to Frequency Detuned Control and Signal Picosecond Pulses
Authors: Tang J.M. , Shore K.A.
Published: February 2023

The optical switch known as the Terahertz Optical Asymmetric Demultiplexers (TOADs) is currently attracting a high degree of interest because of several key developments and new applications such as all-optical regenerative memory. However, rather little theoretical analysis of the operating characteristics of TOADs has been undertaken. Recently analysis which took into account the usual gain saturation and ultrafast intraband processes contributing to nonlinear gain compression, showed that threshold energy of TOADs can be decreased to less than 0.1pJ by matching the width of control pulse and switching window [1], and also that switching windows less than 1ps cannot be achieved in practice due to the effect of ultrafast intraband processes [2].
Quasi-smart Optical Fibre Sensor System for Real Time and Predictive Monitoring on Large Rotating Machinery
Authors: López-Higuera J.M. , Santamaría I. , Cobo A. , Pantaleón C. , Morante M.A. , Ibáñez J. , Echevarria J.
Published: February 2023

A new optical fibre sensor system including the fibre optic transducer, the optical channel, the optoelectronic unit, and a digital data acquisition and signal processing unit (DASPU), that has been fully developed and tested, both in the laboratory and in the field, is presented in this paper. From monitoring vibration on selected places of large rotating machines, the developed system is capable of processing the acquired signals in order to extract significant information for data trend analysis, and to take correction decisions with the aid of specific programs. Fig. 1 shows a schematic view of the system. The transducer operating principle is based on a fibre optic cantilever beam without any seismic mass on it, and a differential intensity modulation scheme that minimises the errors due to intensity undesirable changes and environmental perturbations. The optical fibre accelerometer is optimised for detection of mechanical vibrations in the frequency range 0.2 - 140 Hz, provides very good stability and accuracy, and has the inherent advantages of remote fibre optic sensing and electromagnetic immunity (1).
Integrated waveguide sensor for Biological Assay
Authors: Ruano J. , Ortega D. , Bonar J. R. , Cooper J. M. , Aitchison J. S.
Published: February 2023

Recent progress in the development of a planar form of a the vapour axial deposition (VAD) system, called Flame Hydrolysis Deposition (FHD), has enabled the realisation of a variety of novel optoelectronics devices. In this paper we explore the application of this technology to the production of integrated biosensors, with the possibility of being able to produce optical diagnostic arrays for biochemical screening. Optical biosensors have a number of specific advantages over their electrochemical counterparts, for example: they do not suffer from noise associated with electrical interference, and they provide access to a wide variety of highly specific environmentally sensitive fluorophores. Importantly, in producing an array technology, optical sensors can either be addressed or read in parallel, allowing rapid data acquisition.
Remote analysis of steels and other solid materials using Laser-Induced Breakdown Spectroscopy (LIBS)
Authors: Botheroyd I. M. , Young J. , Whitehouse A. I , Duckworth A.
Published: February 2023

The remote analysis capabilities of Laser-Induced Breakdown Spectroscopy (LIBS) as applied to radioactive materials and/or environments has been previously reported (for example, refs. 1, 2). For remote measurement applications, the laser energy and the plasma light may be delivered / collected using either i) optical-fibres or ii) a telescope arrangement and direct line-of-sight between the LIBS instrument and the target material. We report here the development of two novel LIBS-based instruments; one uses a telescope arrangement and can perform measurements over distances of up to 30 metres in air and another which employs optical-fibres and a miniature remote probe head.
Optical Fiber Long-Period Gratings for the Refractometry of Aqueous Solutions
Authors: Falciai R. , Mignani A.G. , Vannini A.
Published: February 2023

Refractometers are of interest for measuring concentrations of solutions, since the refractive index of a solution is proportional to its concentration. On-line continuous refractometry is important in many industrial processes, as well as for checking the concentration stability of solutions in stock.
Absolute sphericity measurement: a comparative study on the use of interferometry and a Shack-Hartmann sensor
Authors: Pfund J. , Lindlein N. , Schwider J. , Burow R. , Blümel T. , Elssner K.-E.
Published: February 2023

Today the Shack-Hartmann sensor (SHS) has matured to a tool in optical metrology which is able to compete to some extend with interferometry. The comparison of the performance of the SHS and interferometry in absolute sphericity tests is presented.
Monitoring Nd:YAG and CO2 Laser Weld Quality
Authors: Mettke Christoph , Ng Eng S , Watson Ian A.
Published: February 2023

Automated laser welding can be improved by developing sensors that accurately record the weld characteristics and provide a feedback signal to control the laser output appropriately. A number of solutions to this problem have been developed [1,2]. An indicator or set of indicators, representing the weld quality, have to be measured during the weld process and optimised in real time so that constant quality is guaranteed. The main indicators of a good weld are its symmetry, general regularity of the weld bead and the relative spacing between the solidified pool ripples along the bead. Discontinuities such as cracks and porosity characterise a poor weld.
Toroidal Surface Reconstruction Using Ronchi Deflectometry
Authors: Royo S. , Arasa J. , Pizarro C.
Published: February 2023

Ronchi deflectometry is a widely used optical testing technique which has been extensively studied [1]. While lacking of the precision that interferometric techniques provide, its dynamical range allows the measurement of surface slope variations unavailable for interferometers. The technique has been commonly applied to the profilometry of spherical and aspherical surfaces, and phase-shifting techniques have been proposed in order to improve its measurement precision [2].
Dependence on the beam detection position in the beam profile measurement on a rotating optical disk
Authors: Ogawa Akihito , Kubo Takahiro , Sugiura Akinobu , Kaneko Torn , Miura Kenjiro T. , Kawata Yoshimasa
Published: February 2023

With a working drive it is difficult to dynamically measure the beam profile formed on the optical disk because of the rotation of the disk and the movement of optical head due to auto focusing. We have developed the measurement method of the beam profile on a rotating optical disk, which is based on the scanning knife edge method[1]. To apply this method to an actual drive, we proposed two techniques. The first one is to detect the transmission light through the measurement disk with an external PIN photodetector, and the second is to detect the reflection light by using the built-in photodetector of the drive(Fig.1)[2]. The merits and demerits of both measurement techniques are clarified by comparing each other. We present the Influence of the distance between the detector and the disk.
Laser Ablated Silicon Gratings for Temperature Measurements
Authors: Chao Chung-Yen , Chen Cheng-Yen , Liu Chee-Wee , Chang Yih , Yang C. C.
Published: February 2023

In this paper, we report the temperature variation response of silicon grating and the release of thermal strains in such a grating. The periodical corrugations of such a silicon grating were directly ablated by the interference fringe of the fourth-harmonic of a Q-switched Nd:YAG laser. The grating period can be varied from 180 through 550 nm. Such a grating has the application potential for temperature measurement of silicon wafer in thermal process facilities of integrated circuits. We found that the crests in the corrugations were composed of silicon oxide, which could be removed with HF dip. After HF dip, the crests became troughs. Figure 1 shows a typical set of results under the condition of laser ablation with an air gap between a prism and the sample and nitrogen purge. The dark diamonds represent the measurement results before rapid thermal annealing (RTA). The gray diamonds and crosses stand for the results after nitrogen-purged RTA (800 °C for 30 sec) in the increasing and decreasing temperature measurements, respectively. We can see that the variations of the data points are consistent with theoretical predictions. Notice that after RTA the room temperature grating period has been increased implying that in this case the built thermal strains become compressive. Then, the gray triangles and X marks in Fig. 1 stand for the results after nitrogen-purged RTA (800 °C for 30 sec) and after 30 sec 10 % HF dip in the increasing and decreasing temperature measurements, respectively. Now, the room temperature grating period is reduced back to the value before RTA implying that the existence of oxide causes tensile strain after RTA. It was found that the results relied on the environmental condition and laser pulse energy during grating formation. The details of silicon oxida-tion and the release of thermal strains will be reponed.
Self-homodyne linewidth measurements using a short delay line
Authors: Ludvigsen Hanne , Tossavainen Mika , Kaivola Matti
Published: February 2023

The delayed self-homodyne detection technique gives a convenient method to study the linewidth of laser sources. We have performed linewidth measurements on a 1.55-µm noncommercial multi-quantum-well DFB laser using the modified homodyne technique with delays short and by comparing with the coherence time of the laser [1]. The setup includes a phase modulator to average out the critical dependence on the phase matching of the interfering fields when using a short delay. Furthermore, in the detection stage the signal is shifted up to a carrier frequency by an RF-oscillator and a mixer to allow the use of a standard spectrum analyzer. A fit of a theoretical model to the measurement data gives a value for the linewidth.
Single frame phase-shifting speckle-interferometer with a diffractive element
Authors: Kranz J. , Hettwer A. , Lamprecht J. , Schwider J.
Published: February 2023

Speckle-interferometry is a sophisticated technique for the non-contact, high precision measurement of form, deformation and vibration of technical surfaces. In the following, a new single frame phase-shifting speckle- interferometer for the quantitative measurement of out-of-plane-deformations is described /1/. Six interference patterns are acquired within the frame time of a single CCD-camera, thus minimizing the influence of thermal fluctuations and vibrations of the object.
White-Light Continuum Spectral Interferometry for Dispersion Characteristics Measurements in Anisotropic Crystals
Authors: Delbarre H. , Przygodzki C. , Boucher D.
Published: February 2023

White-light spectral interferometry has been recently demonstrated to allow a very precise determination of dispersion [1, 2]. In usual isotropic materials (glass), the use of a correct dispersion rule (Sellmeier or Cauchy formula for instance) in a nonlinear fitting procedure can lead to an enhanced accuracy (of the order of 10−5) for the indices.
Demonstration of Multi Wavelength Picosecond Pulse Generation with resonant RF drive using an Monolithically Integrated Multi-Grating Cavity (MGC) Laser
Authors: Owen M. , Penty R.V. , White I.H. , Poguntke K.R. , Robertson M.J.
Published: February 2023

Multiwavelength optical sources have potential applications in both Wavelength Division Multiplexing (WDM) and Optical Time Division Multiplexing (OTDM) transmission systems. To date sources able to generate multiwavelength picosecond pulses have been demonstrated using external cavity grating lasers [1]. Here, multiwavelength pulses are generated using a monolithically integrated device, which is able to lase simultaneously on four WDM channels.
Harmonic modelocking at up to 440GHz repetition rates in InGaAs-InAlGaAs quantum well lasers
Authors: McDougall S. D. , Ironside C. N. , Bryce A. C. , Marsh J. H. , Vögele B. , Stanley C. R.
Published: February 2023

The InGaAs-InAlGaAs quaternary quantum well material system forms an alternative to the conventional InGaAsP based diode lasers for use in 1.3µm and 1.55µm fibre optic systems. Larger conduction band offsets and a greater thermal stability compared to the InGaAsP system makes InAlGaAs material attractive for both high speed modulators [1] and room temperature high power lasers. In this paper we present the first demonstration to our knowledge of monolithic modelocking action from InGaAs-InAlGaAs laser diodes.
Temperature Dependence of the Self-Pulsating Characteristics of Compact Disk Laser Diodes
Authors: Lynch S. A. , McEvoy P. , Landais P. , O’Gorman J. , McDonald D. , Donegan J. , Hegarty J. , Elsäßer W.
Published: February 2023

Extensive research has been performed, with varying success, to develop red laser diodes which exhibit strong self-pulsation over an extended temperature range (0 - 80 °C) for optical storage applications. As an approach to understanding this problem we have investigated the dependence of self-pulsation characteristics in commercial CD laser diodes emitting at λ = 780 nm, when operated between T = 77 K and T = 310 K. Self-pulsation in these devices was found to extinguish below about T = 100 K. Measurements of the variation of self-pulsation frequency (vsp) with bias current in the temperature range 150K to 310 K. (Fig. 1) showed a more sensitive dependence on bias current as the heatsink temperature decreases. When this data was viewed (Fig. 2) in the more conventional form, vsp versus normalised bias current (I/Ith - 1), it is clear that the slope of these curves are not strongly temperature dependent. These results are interesting since it is commonly assumed that the selfpulsation frequency in CD laser structures occurs at the laser diode modulation resonance frequency (ΩR) which predicts a quadratic dependence of normalised bias current on ΩR and a temperature dependence of the slope due to the well known temperature dependence of carrier life - neither of which are apparent.
Periodically Poled RbTiOAsO4 Femtosecond Optical Parametric Oscillator Tunable from 1.38 to 1.58 µm
Authors: Loza-Alvarez P. , Reid D. T. , Ebrahimzadeh M. , Sibbett W. , Karlsson H. , Henriksson P. , Arvidsson G. , Laurell F.
Published: February 2023

High average output power femtosecond sources operating across the 1.5 µm telecommunication band are restricted mainly to colour-centre lasers, Kerr-lens modelocked Cr+4:YAG oscillators and optical parametric oscillators (OPOs). The need for cryogenic conditions limits the versatility of colour-centre-based souces and practical difficulties have made self modelocked operation of Cr−4:YAG lasers near the 1.4 µm water absorption band very difficult to sustain. In contrast, the OPO that we describe in this paper operates at room temperature and is continuouslv-tunable over 200 nm from 1.375 to 1.575 µm using only a single cavity mirror set. The OPO is based on periodically poled RbTiOAsO4 (PPRTA)1. The crystal used had a grating period of 30 µm and dimensions 5 mm long × 0.5 mm width × 5 mm high2. The crystal was antireflection coated for a wavelength of 1.1 µm and we estimate that the loss of each surface at a wavelength of 1.5 µm to be ~1 %. The OPO was synchronously pumped by a modelocked Ti:sapphire laser at a repetition rate of 84 MHz. with output pulses of 100 fs duration and centred at a wavelength of 850 nm. We used a 90 mm focal-length lens to focus the pump beam in to the PPRTA crystal. The polarisation of the pump, signal and idler wavelengths were all horizontal in the cavity and parallel to the poling direction which lay along the crystalographic c axis. The dispersion-compensated OPO cavity consisted of two SF14 prisms, two curved mirrors (r = 100 mm) and one flat mirror as the output coupler. All the mirrors were high-reflecting at the central wavelength of 1.5 µm.
Tilted pulses and X(2) cascading: effects on transient compression and temporal-soliton formation
Authors: Danielius Romas , Di Trapani Paolo , Dubietis Audrius , Valiulis Gintaras
Published: February 2023

In X(2) cascading, two relevant phenomena are expected in case of suitable group-velocity mismatch (GVM) and group-velocity dispersion (GVD) material parameters: (i) if the GVM dominates and the low-frequency pulses run with opposite velocities respect to the high-frequency one, then interaction could lead to the so called “non-linear transient pulse compression” or to the elastic scattering of non-trapped soliton pulses, (ii) If the GVD dominates and has the same sign for all three waves, then mutually-trapped dispersion-free bright solitons (or quasi-solitons) are attained, due to the interplay between GVD and nonlinearity. Unfortunately, such operating conditions are hardly achievable in real experiments. Non-linear pulse compression was demonstrated only for very specific crystals and wavelengths; regarding the GVD solitons, they are commonly considered as not obtainable due to the low intrinsic dispersion of available X(2) materials, which makes the GVM split the interacting pulses before the trapping mechanism sets in. For a review of the argument, see ref. [1] and references therein.
Beam Quality Characteristics of Solid State Lasers
Authors: Eppich B. , Weber H.
Published: February 2023

The output of high average power lasers, especially solid state lasers, constists of many coherent modes, fluctuating in time and space. Easily to detect is only the time averaged intensity J(x,y) = . With knowlodge of J(x,y) alone it is not possible to predict the propagation of such beams. On the other hand for beam transportation and beam application at least the transverse beam diameter is required. In a first approach the diameter and its propagation through ABCD-optics can be calculated from the 10 second order moments of the beam But for all technical applications the power content values are of major interest, and there is no close relation to the second order moments.
High Power Visible Solid-State Lasers
Authors: Clarkson W. A.
Published: February 2023

Visible light generation via nonlinear frequency conversion of diode-pumped solid-state lasers is an area which has attracted growing interest over recent years owing to the numerous applications tor such sources in areas such as display technology, medicine and optical pumping of solid-state lasers. For many of these applications the requirement for high average power, as well as high efficiency and wavelength diversity, has itself resulted in numerous developments in power-scaling of solid-state lasers and in techniques for efficient nonlinear frequency conversion, including novel nonlinear materials such as periodically-poled lithium niobate.
Pr,Yb:ZBLAN Upconversion Fibre Amplifier with 1.38 W of Output in the Red Spectral Range
Authors: Scheife H. , Heumann E. , Heine F. , Sandrock T. , Petermann K. , Huber G.
Published: February 2023

Upconversion-pumped Pr.Yb-doped ZBLAN fibres have attracted increasing attention recently because of their ability to produce high-power laser output in the visible spectral range, namely at a wavelength of 635 nm [1]. Possible applications include display technology and optical communication as well as medicine. Many of these require modulated laser output. In principle, this can be achieved by introducing acousto-optical or electro-optical devices in the output beam. Unfortunately, the first method imposes a serious limitation on the maximum attainable modulation frequency, while the second requires linearly polarized light to be applicable without excess losses. Alternatively, direct modulation of a low-power diode laser seeding a fibre amplifier (Master Oscillator Power Amplifier configuration) should lead to high-frequency modulated high-power output. We report on a Pr.Yb:ZBLAN fibre amplifier seeded by a 635 nm diode laser.
Grating competition in photorefractive polymers.
Authors: O’Leary S.V. , Smith M. A. , Mitchell G. R.
Published: February 2023

We have investigated photorefractive two-beam coupling (TBC) and degenerate four-wave mixing in a new photorefractive polymer (PRP) material. The observed dependence of grating diffraction efficiency on applied poling field differs strongly from that predicted by standard models, exhibiting a sharp decrease with field over a certain range of field values. We describe a model which incorporates competition between photorefractive gratings and photoisomerization gratings in the material and which accounts for the observed behaviour satisfactorily.
Nonlinear Cross Talk Between Mutually Incoherently Recorded Gratings In BaTiO3
Authors: Limeres J. , Carrascosa M. , Andersen P. E. , Petersen P. M.
Published: February 2023

Recently, nonlinear coupling of simultaneously coherently recorded gratings in photorefractive BSO has been studied experimentally and theoretically [1]. This so-called nonlinear cross talk is induced through the nonlinear response of the photorefractive material. In applications involving multibeam interactions, such as photorefractive image amplification and holographic storage, the nonlinear cross talk may strongly affect the grating efficiencies. Previous interpretations of multibeam experiments in BaTiO3 are based entirely on beam coupling, which may lead to a disagreement between theory and experiments [2].
Broad Spectrum Two-Wave Mixing in BaTiO3
Authors: Danailov M.B. , Pecchia A. , Laurito M. , Apai P.
Published: February 2023

Two-wave mixing (TWM) in photorefractive crystals has been widely studied in the last decade and many potential applications have been demonstrated. As a rule, narrowband lasers with large coherence length have been utilised. To our knowledge, in the literature there is practically no data on the performance of TWM when lasers with spectral width of several nm or more are used.
Microsecond duration free carrier induced gratings in CdMnTe
Authors: Moussu C. , Zaquine I. , Maruani A. , Frey R.
Published: February 2023

Very efficient gratings can be recorded in semiconductor media due to the huge dependance of the refractive index with respect to carrier density. However, due to the fast diffusion of the photogenerated carriers, the lifetime of these gratings is small (from the picosecond to the nanosecond range).
Quantum Cascade Lasers
Authors: Sirtori C. , Collot P. , Nagle J. , Faist J. , Capasso F.
Published: February 2023

By controlling the quantum well widths and the tunnelling barrier thickness of heterostructures it is possible to create artificial potentials where level separations, dipole matrix elements, lifetimes and scattering times are dependent on the potential design. This allows us to conceive new materials (material by design) where electronic and optical properties can be tailored not only for demonstrate new physical effects but also to optimise device performance. The Quantum Cascade (QC) laser is an excellent example of how quantum engineering can be used to design and develop new laser material in the mid-ir. After the first demonstration of Quantum cascade lasers a strong effort has been done to improve the performance of this mid-ir source which is now ready to be exploited into sensing systems for molecular detection in the atmospheric windows (3 - 5 µm and 8 - 13 µm). Room temperature operation1,2, high peak power2 and DFB lasers4 have been demonstrated, making this laser the first room temperature mid-ir coherent semiconductor source operating single mode in the 5 - 9 µm range.
2.0 - 2.4 µm High-Power Broaden Waveguide SCH-QW InGaAsSb/AlGaAsSb Diode Lasers
Authors: Garbuzov D. , Lee H. , Khalfin V. , Martinelli R. , Menna R. , Connolly J.
Published: February 2023

In this paper we describe a new design for mid-infrared quantum well (QW) diode lasers which has led to CW operation of 2.0 - 2.4 µm devices at temperatures as high as 100° C. Maximum output power levels of 1.9W and 0.5W and differential quantum efficiencies of 53% and 30% have been achieved at 2.0 and 2.3 µm, respectively. The InGaAsSb/AlGaAsSb devices were grown by MBE on n-GaSb substrates. The first report of lasing at wavelengths exceeding 2 µm was by H. Choi et al.[1] In their structure the multi-quantum well (MQW) active region is located near the AlGaAsSb cladding layers. This structure design significantly reduces carrier leakage from the QWs but. at the expense of increased optical losses since more than 90% of lasing mode propagates in layers with high free carrier concentration. Our recent studies of 2 µm InGaAsSb/AlGaAsSb lasers has revealed that AlxGa1-xAsySb1-y waveguide layers with Al compositions as low as 30% can provide efficient carrier confinement in InGaAsSb QWs [2].
1.3 µm InGaAsP/InP MQW Lasers for High Temperature Operation Experiment and Modeling
Authors: Belenky G. , Donetsky D. , Reynolds C. , Shtengel G. , Kazarinov R. , Luryi S.
Published: February 2023

We carried out growth, fabrication, as well as characterization and modeling of InGaAsP/InP lasers with 9 QW active region and different p-doping profiles within the temperature range of 10 - 80 °C and the range of injection current densities up to 10 kA/cm2. Measurements of the threshold current, external efficiency, and optical loss were carried out for broad area and capped mesa buried heterostructure devices. We used broad area devices with electron collector on the top of p-contact for leakage measurements [1] and a modified Andrekson technique to measure optical loss. For simulation we used “Padre” program based on drift-diffusion approximation. Experiment shows that for devices with moderately doped SCH, the threshold current at room temperature reaches the value of 115 A/cm2 per QW and T0 = 64K (Fig.1).
Interwell carrier transport in InGaAsP quantum well lasers: effect of valence band barrier height
Authors: Silfvenius Christofer , Marcinkevičius Saulius , Landgren Gunnar
Published: February 2023

Interwell carrier distribution is a process of major importance for the operation of multiple quantum well (MQW) lasers. For a laser to operate effectively, a uniform carrier distribution in all the wells is needed. However, previous studies have shown that for both, cw and pulsed current injection, carrier densities in different wells are not equal. The main reason for such effect is a slow interwell hole transport.
Time-resolved photoluminescence study of 1.58 µm InGaAs/InGaAsP quantum wells
Authors: Molloy C.H. , Somerford D.J. , Blood P. , Wood A K
Published: February 2023

In this paper we report direct measurements of carrier recombination at 1.58 µm via time-correlated single photon counting using a Ge single-photon avalanche photodiode with time resolution of 300 ps. Under high optical excitation, this provides a means for assessing the contribution of Auger processes. These are believed to play a role in the high temperature sensitivity of 1.5 µm lasers although to what extent remains unclear. The strained (1% compressive) and unstrained samples mimicked our laser structures (four and 5 30 Å InGaAs quantum wells with 150 Å InGaAsP barriers lattice matched to InP) but were nominally undoped throughout (background~5 × 1015 cm−3,n-type) Fits to the data were calculated using the initial photogenerated earner density (Δn(t=0)) and Auger coefficient (CA) as fitting parameters and included radiative, extrinsic non-radiative and Auger recombination. For example, fitting the room temperature photoluminescence decay for a strained sample gave CA= 1.0 × 10−28 cm6 s−1 and Δn(t=0) = 3.5 ×1017 cm−3, typical of the sample set. At this initial carrier density, Auger accounts for 13% of the total recombination. Fit quality is degraded if Auger recombination is omitted. This value for CA is greater than previously measured (1.3 × 10-29 cm6 s-1 [1]), and has important implications for laser operation. In order to explore the relation between the time-resolved photoluminescence results (TRPL) and the laser devices in more detail, we have studied lasers with similar layer structures to the time-resolved photoluminescence samples and cavity lengths the range 300- 1160 µm. The temperature dependence of the threshold current shows two distinct regions; for T=230-340K threshold current increases exponentially with temperature, whilst above 340K it increases super-exponentially. By comparing these results with the TRPL studies as a function of temperature we are able to assess the relative contribution of Auger recombination in these samples.
High-Bit-Rate, Transform-Limited Pulse Trains by Intracavity Laser Frequency Modulation
Authors: Longhi S. , Taccheo S. , Sorbello G. , Laporta P.
Published: February 2023

Generation of high-repetition-rate, transform-limited picosecond pulse trains is of major concern for applications in soliton-based optical transmission systems. Active mode-locking of semiconductor or erbium lasers is a well-assessed technique, but it is generally affected by stability problems related to the intrinsic resonant nature of this method, in particular when phase mode locking is adopted [1].
High-power self-starting femtosecond Cr:forsterite laser
Authors: Petrov V. , Shcheslavskiy V. , Noack F. , Mirtchev T. , Itatani T. , Sugaya T. , Nakagawa T.
Published: February 2023

Owing to its broad tunability and useful fundamental and second harmonic wavelengths, Cr:forsterite (Cr4+:Mg2SiO4) lasers are attracting a lot of attention in the ultrafast science. However, self-starting operation of relatively low power Kerr lens mode-locked femtosecond Crforsterite lasers using semiconductor saturable-absorber mirrors (SESAM’s) was reported only recently [1,2]. We scaled the parameters of this purely passive technique and achieved simultaneously output energies on the 10-nJ level and sub-100 fs pulse durations. The high contrast of these pulses allowed for the first time efficient direct frequency conversion to the 600 nm region with efficiency as high as 30%.
Transverse optical modes of a RF excited Ar-Xe laser: experiment and theory
Authors: Elkin N.N. , Kochetov I.V. , Napartovich A.P. , Troshchieva V.N. , Blok F.J. , Peters P.J.M. , Starostin S.A. , Udalov Yu.B. , Witteman W.J.
Published: February 2023

With respect to the propagation of a laser beam a slab-shaped laser medium may be considered as a waveguide in the transverse direction (narrow spacing) and as free space in the lateral direction (broad area). Using a common procedure of separation of variables, the mode formation in the transverse and lateral direction may be considered independently. The excess energy from the excited region should be removed by heat conduction to the walls resulting in the formation of refraction index gradients. The index gradients may strongly influence the waveguide mode shape and loss. On the other hand, the minors of the resonator are placed at some distance from the waveguide ends. Therefore, a cavity mode generally is formed as a result of the combination of free-space diffraction (FSD), the reflection from the resonator mirrors and waveguide propagation (WP). Losses are controlled by absorption in the waveguide walls, coupling of radiation reflected from the mirror to the waveguide and output coupling. In this paper numerical simulations of a cavity consisting of an index-graded waveguide and two plane mirrors were performed. Calculations were made for typical experimental conditions: a RF discharge pumped laser on atomic Xe lines (2.03, 2.65 and 3.51 µm); gas mixture He-Ar-Xe at pressure 0.15 bar, waveguide transverse width 2 mm, active medium length 37 cm. Beam profiles were measured in the far and near field zones with a one-dimensional photodetector array (128 elements 200 pm each)1. Typical experimental results for the 3.51 µm line for two array positions are presented in Fig. 1, along with the results of numeric calculations. In the computations the index profile, gas composition and distances between waveguide and mirrors were varied. The effect of a possible non-uniform distribution of the gain will be discussed.
High spatial and temporal coherent output from a broad-stripe laser diode with phase conjugate feedback
Authors: Hatano Satoshi , Omatsu Takashige , Hasegawa Akira , Tateda Mitsuhiro , Ogura Iwao
Published: February 2023

We report the first demonstration, to our knowledge, of high bright output with low M2 and narrow linewidth from a broad-stripe laser diode (BS-LD) with a phase conjugate feedback. Fig. 1 is the experimental setup. A 1W-class BS-LD (SONY SLD304), whose polarization is parallel to die y-axis in Fig.1, is mounted onto heat sink. The output of BS-LD is collimated and passes through a half wave plate, which rotates the polarization by 90°, so that the polarization of BS-LD lies in an undoped BaTiO3 extra-ordinary plane. One-half of BS-LD beam is out-coupled by a prism mirror placed in the far field, and the other is focused onto the BaTiO3. The BaTiO3 has dimensions of 5mm × 6mm × 7mm, and operates as a self-pumped CAT phase conjugator. The free-running BS-LD had 1.5nm line-width (FWHM) and poor beam quality of Mx2~5 and My2>100 in the directions along the x and y-axes. After the BS-LD switching on, the phase conjugator turned on within 10minutes. After an additional 5-10minutes, the system reached a steady state and the line-width of BS-LD had narrowed to less than 0.3nm (Fig.2). The out-coupled beam, which was focused by a lens with the focal length of 100mm, is shown in Fig.3. Its Mx2 and My2 factors had reduced to less than 20% and 35% compared with them at free-running. And then, out-coupled power still exceeded 50% of the total lasing power of BS-LD. It means that the focused output beam should have 7 times higher brightness than at free-running. Previously beam-clean-up of a high-power-array-laser-diode with phase conjugate feedback has been reported. In previous reports, because the phase conjugator works not as spatial filter but just as self-alignment external feedback mirror, an additional spatial filter was required for picking off one-half of twin-lobe output in far-field. Our technique is very different from previous ones, because it required no element such as the spatial filter for improving beam quality and narrowing the lasing frequency in BS-LD apart from the external phase conjugator. We therefore conclude that the BS-LD with phase-conjugate feedback is an effective source for pumping solid state laser materials at high efficiency.
The application of the Strontium-Barium-Niobate nonlinear crystal to control the laser emission in the red and near infrared range
Authors: Bufetova G.A. , Ivleva L.I. , Nikolaev D.A. , Osiko V.V. , Poloskov N.M. , Seregin V.F. , Shcherbakov I.A. , Tsvetkov V.B.
Published: February 2023

The idea to use the holografic gratings, written in the volume of the crystals to control the laser emission for the goals of communication seems to be very attractive. However the use of high efficient photorefractive crystals is very difficult because of the low value of the absorption coefficient in the red and infrared spectrum range.