bluuebunny/crossref_metadata_2025 huggingface dataset:
An Optimized Diode-Pumped BaY2F8:Er3+(7.5 at.%) Laser at 2.8 µm
Authors: Wittwer S. , Pollnau M. , Spring R. , Lüthy W. , Weber H. P. , McFarlane R. A. , Harder Ch. , Meier H. P.
Published: February 2023

The potential surgical applications of 2.8-µm radiation due to its strong absorption in water and thus in biological tissue has motivated the investigation of laser operation in erbium-doped host materials. Modem surgical applications demand a compact laser system with high output power. GaInAs diode lasers at 970 nm are an excellent pump source for Er3+ lasers and allow the desired compactness.The best pump wavelength for an erbium 3-µm laser is 970 nm leading to a transition into the upper laser level [1]. Fluoride hosts promise high efficiency .This has been confirmed by several experiments, that have been raising the efficiency in LiYF4:Er3+ up to 40 % [2] with Ti:sapphire-pumping and 35 % [3] with diodepumping. The optimization of the slope efficiency for LiYF4:Er3+ lasers is still assumed to proceed towards the theoretically predicted efficiency maximum of 56 % [4]. Efficient lasers are also reported in BaY2Fg: Er3+. For this crystal we expect a similar efficiency as in LiYF4: Er3+, especially for optimized erbium concentrations of 10 to 15 at.% [5].
Modeling Laser Diode Pumped Er, Yb: Glass Lasers
Authors: Hamlin Scott J. , Wu Ruikun , Hutchinson J. Andrew , Marshal Lawrence T.
Published: February 2023

Er,Yb:Glass is a unique laser gain media. Er,Yb:Glass is used for the direct generation of eyesafe 1.54 µm laser radiation. Er3+, when doped into a phosphate glass matrix, lasses from the 4I11/2 metastable energy level to the 4I15/2 ground level, utilizing a three level laseing scheme. To achieve inversion, more than half of the Er3+ ions must be in the metastable energy level. To obtain reasonable pumping energies, the Er3+ dopant concentration is usually quite low in comparison to other rare earth doped solid state lasers. As the concentration of Er3* is low and the absorption cross-section of Er3+ in glass is also quite low, it is very difficult to directly pump any of the Er3+ absorption lines. Fortunately, the transfer efficiency of energy from the 2F5/2 level of Yb3+ to the 4I11/2 energy level of Er3+ is nearly unity. Although the absorption cross-section of Yb3+ is similar to Er3+, the doping concentration of Yb3+ is usually more than several orders of magnitude greater than Er3+. The addition of Yb3+ to the glass matrix has a minimal effect upon the absorption at the lasing wavelength. The combination of long fluorescent lifetime and broad spectral absorption make Er,Yb:Glass an ideal media for laser diode pumping. The largest challenge to a Laser Engineer is the low thermal conductivity of the glass matrix.
30 nm continuous tuning range with an external cavity diode laser at 770 nm
Authors: Laschek M. , Kohrs A. , Tünnermann A. , Wandt D. , Welling H.
Published: February 2023

External cavity diode lasers are attractive light sources for many applications in metrology, high resolution spectroscopy and gas monitoring because they have small linewidths and broad tuning ranges in combination with a compact size, a simple handling and a high operation lifetime. By using different near-infrared laser diodes as active material, those systems are tunable over a broad wavelength range. In addition, wavelength tuning without mode hops can be achieved by using suitable resonator configurations.
Dispersion in optical fibre directional couplers
Authors: Chiang Kin S.
Published: February 2023

Directional couplers are the most widely used passive devices in modern optical fibre transmission systems. However, the dispersion effects in a directional coupler have not been thoroughly investigated. Recent work [1] indicates that the common understanding, i.e., the disperison in a coupler is governed by the group-velocity dispersion, is not correct. In this paper, it is argued with the coupled-mode theory that pulse distortion in a coupler is caused mainly by the frequency dependence of the coupling coefficient.
A Microwave Photonic Phase Shifter With Wideband Signal Processing Applications
Authors: Winnall S. T. , Lindsay A. C. , Knight G. A.
Published: February 2023

A photonic microwave phase shifter exploiting vector modulation has been constructed. The device is capable of shifting an arbitrary input signal through greater than 2π phase shift across 2-18 GHz. To illustrate applications of the device, the basic phase shifter was then incorporated into frequency translation and frequency discrimination architectures.
Actively Mode-Locked Diode-Pumped Nd:YAP Laser
Authors: Kubeček V. , Guy O. , Barthelemy A.
Published: February 2023

Actively mode-locked diode pumped solid state lasers are of great interest for communications, detection and ranging, electrooptic - sampling, spectroscopy, biology and other applications. For mode-locked emission the key parameters concern the spectroscopic features of the laser active medium crystal and the efficiency of the electro or acousto-optic modulator.
Double-Frequency Harmonic Mode Locking in a Pulsed Nd:YAG Laser
Authors: Di Trapani P. , Amati S. , Bondani M. , Andreoni A. , Cavalcabo G. , Zanzottera E.
Published: February 2023

The harmonic mode locking (ML), i.e. the modulation of resonator losses at a frequency that is an integer multiple N of the fundamental mode spacing, has been a technique intensively studied for achieving minimum pulse duration in low-gain actively mode locked continuos wave (CW) Nd:YAG laser (see refs. [1, 2] and references therein). The experiment we have performed concerns the first demonstration of the harmonic ML on an high-gain QS Nd:YAG laser, operated at 10 Hz repetition rate. To avoid the generation of several pulses per round-trip we implemented the ML by simultaneously operating two phase-locked acousto-optic modulators (AOM) with N=3 (radio frequency: RF=150 MHz) and N=4 (Rf=200 MHz), placed at 1/3 and 1/4 of the resonator length, respectively. By operating a stable cavity in QS ML regime we observed that the short buildup time allowed by the QS was not sufficient to let the ML to evolve to the stationary regime, so that the generated pulses resulted surrounded by a≈1 ns long pedestal and satellites exist placed at 1/3 and 1/4 of the cavity length. To increment the build-up time we realised a simple kind of prelasing by slightly rotating the QS quarter-wave plate and letting the laser starting to oscillate in free running (FR) ML regime. When the first FR spike was developed, a photodiode triggered the QS to allow the seeding pulse to be amplified up to gain saturation. The amplified ML train contains 4-5 pulses whose duration, measured by SH scanning autocorrelation, was =100 ps FWHM. A typical autocorrelation trace is given in Fig. 1. No satellites were present in this regime. With the laser operated with 80% output coupling, the maximum pulse-train energy, set by the damage threshold of resonator optics, was ≈10 mJ. The shot-to-shot energy fluctuations at the fundamental wavelength were below 5%, while below 8% those at the SH, indicating the high energy and temporal stability's of the generated pulses.
High-Gain Double-Pass Pulsed Dye Amplifiers For Laser Guide Stars
Authors: Kapitan D. , Coutts D.W. , Webb C.E.
Published: February 2023

Laser guide stars (LGS) are required to obtain complete sky coverage for astronomical telescopes incorporating adaptive optics. Resonant scattering of a high power pulsed laser from atomic sodium in the mesosphere is the most promising technique for the production of a LGS. However, due to saturation of the sodium layer, the efficient generation of a bright LGS using pulsed excitation is difficult. We are devising a modular system where the brightness of the LGS can be increased linearly by adding more laser units [1]. A frequency-locked cw dye laser acts as a master oscillator (MO) which is alternately pulsed amplified through an array of dye amplifiers by means of time-multiplexing thus creating a pulse-train. Consequently, the peak power of each pulse does not increase when the average power is scaled to give a larger photon return from the LGS.
Polarizer based on the dielectric layer with surface-relief grating for microchip Nd:YAG/KTP laser with mode-selective birefringent filter
Authors: Bel’tyugov V.N. , Leis A.V.
Published: February 2023

The diode laser pumped Nd3+ solid-state laser with intracavity frequency doubling in KTiOPO4 (KTP) is attracted recently much attention. This laser can be used for the realizing of compact and stable green laser source. Unfortunately, the laser has an amplitude instability in the second-harmonic output due to longitudinal mode coupling through sum-frequency generation1. This problem can be eliminated by allowing only single mode operation. One of the techniques is to use a birefringent filter formed with a polarizer and KTP-crystal as a waveplate. Earlier, a Brewster angle cut Nd:YAG crystal2 and an off-axially cut Nd:YVO4 crystal3 were suggested as a polarizing elements. These ways made the laser geometry more complicated.
6.5 GHz integrated-optical frequency shifter for λ=1.5µm
Authors: Stolte Ralf , Ulrich Reinhard
Published: February 2023

An integrated-optical frequency shifter for λ= 1.5µm and a frequency shift of f
mod
= 6.5GHz has been designed in Ti:LiNbO3 technology. An optical input wave (carrier) at frequency f
in
is electro-optically converted to an output wave (sideband) at f
out
= f
in
± f
mod
. Both waves propagate at orthogonal polarizations in the same stripe waveguide. Conversion is effected by an electrical wave of frequency f
mod
, counter-propagating to the optical waves on a coplanar transmission line. The 3-wave interaction is phase-matched if where Δβ=βc-βs is the waveguide birefringence (βc, βs, propagation constant of carrier and sideband), Ngr is the mean index of optical group velocity, and n
el
is the ‘effective index’ of the electrical wave. Phase matching is practically achieved by adjustment of the dimensions of the transmission line and of Δβ. In the x-cut, z-propagating LiNbO3 substrate, Δβ could be controlled by adjustment of the width w of the Ti stripe. The birefringence was measured by scanning a polarization coupling perturbation along the waveguide while analyzing the polarization of the output signal [1]. Polarization controllers are applied to the pigtails so that the incident signal can be adjusted to either TE or TM polarization. In this way TE/TM or TM/TE conversion can be selected. Due to the reversal of tire sign of Δβ between these two cases the device operates either as frequency up- or downshifter.
Broadband EDFA With Flat Gain Response
Authors: Pan J. J. , Shi Yuan
Published: February 2023

Dense WDM techniques in lightwave networks increase transmission capacity and improve system flexibility. Gain flatness of conventional EDFAs limits the number of WDM channels. Several techniques1,2 for EDFA gain equalization have been investigated, but with various shortcomings. This paper reports a double-pass EDFA with a flat-gain and) a high saturated output signal power.
Anomalous Optical Properties of Water at 40°C and 1.06µm
Authors: Yeo C.B. Allen , Watson Ian A , Wang Ruikang K.
Published: February 2023

The temperature dependency of the optical properties of water plays an important role in understanding laser-tissue and laser-bacteria interactions. Recent interests in laser inactivation or sterilization [1,2] have shown that lasers offer specific advantages over conventional sterilization techniques, for example, autoclaves. The laser sterilization mechanism has not yet been elucidated, however, but it is clear that the mechanism will be wavelength dependent. With excimer lasers, operating in the UV, it is likely to be the normal UV sterilization process (254-260nm) in which thymine dimers inhibit correct replication of the DNA during the cell's reproduction. Lasers operating in the IR (Nd:YAG, CO2) have been shown to exhibit a bactericidal capacity. This mechanism is probably partly thermal. Present efforts to model the interaction of the laser radiation and bacteria have been hindered by the availability of suitable data. To overcome this problem, the present work was initiated to determine the temperature dependency of the absorption and scattering coefficients of water, the principal constituent of bacteria, and used to develop models of the laser sterilization process for the Nd:YAG laser operating at 1.06µm.
Diagnostic of strongly scattering media with diffusely backscattered polarized light
Authors: Hielscher Andreas H. , Mourant Judith R. , Bigio Irving J.
Published: February 2023

That polarization effects in scattered light can yield useful information about biological material has been shown as early as 1976, when Bickel et al. announced a "new biophysical tool" [1]. Surprisingly, very few authors have used this new tool. Only a couple of studies exist that are concerned with polarization of forward scattered and transmitted light [2-3]. However, there are many biomedical applications where only backward scattered light is available for diagnostics, as, for example, in most endoscopic procedures. In this study we demonstrate that different particle size and concentrations lead to differences in the spatial pattern of backscattered light when viewed through a polarizer. These differences can be explained by Rayleigh and Mie theory, and can be used to characterize strongly scattering media like biomedical cell suspensions and tissues.
Adaptive Photorefractive Crystals Based Fabri-Perot Cavities for High-Sensitivity Phase Modulation Detection.
Authors: Jimenez L. , Mondragon J. Sanchez , Stepanov S.
Published: February 2023

Fabri-Perot cavities efficiently accumulating laser beam power are considered promising for different applications where extra-high sensitivity detection of phase modulation is needed, and in particular for detection of gravitational waves, in laser vibrometry in general, in fiber optical sensors etc. Recently utilization of photoreferactive shifted phase holograms was suggested for these configurations [1] which solves the problem of adjustment of the cavity to the resonance with the laser frequency and compensates aberrations introduced by elements of the cavity.
Optical Transistor Based on a Photorefractive Ring Cavity
Authors: Belić Milivoj R. , Petrović Milan , Leonardy Jörg , Kaiser Friedemann
Published: February 2023

The invention of electronic transistors revolutionized the field of electronics. There have been many attempts to achieve transistor action in different optical circuits [1]. Photorefractive materials possess features (strong response at low power levels and parallel processing) which are convenient for realization of optical circuits that, are functionally similar to different, electronic devices [2]. We use these advantages to propose an optical transistor based on a bidirectional PR ring resonator, whose operation is functionally similar to the operation of a bipolar junction transistor.
Intracavity frequency-doubled Yb,Er:LiYF4 upconversion-pumped laser at 617 nm
Authors: Heumann E. , Möbert P. , Huber G.
Published: February 2023

Applications in full-color laser displays raise intense interest in the development of compact-all-solid-state-lasers to produce radiation in the visible spectral region. A promising way of generating visible output is to exploit upconversion processes in infrared-pumped rare-earth-doped crystals and optical fibers or to frequency-double the IR-output of such materials. Up to now, laser output in the red spectral range could be achieved at room-temperature in Tm3+:LiYF4(YLF) at 650 nm and in Yb3 -sensitized Tm3+:BaY2F8 at 649 nm under continuous-wave upconversion pumping [1,2]. Continuous-wave red output at room-temperature could also be demonstrated under dual-wavelength infrared pumping in a Pr3+-doped fluoride fiber at 635 nm [3] and under upconversion pumping in a Pr3+/Yb3+-doped ZBLAN fiber at 615 and 635 nm [4]. Recently, upconversion pumped laser oscillation at 639.5 nm was demonstrated in Pr3+,Yb3+:YLF [5].
Waveguiding and Crystallographic Properties Of Single Crystal Ti:Sapphire Lavers Produced by Pulsed Laser Deposition.
Authors: Anderson A. A. , Eason R.W. , Jelinek M. , Hickey L.M.B. , Grivas C. , Fotakis C. , Rogers K. , Lane D.
Published: February 2023

Layers of Tr:Sapphire with thicknesses between 1 and 82 microns have been produced by the Pulsed Laser Deposition (PLD) of a bulk Ti:Sapphire target (0.1 wt. %) onto nominally pure sapphire substrates of (0001) orientation. These were grown in ambient oxygen at around 10-4mbar using a KrF excimer laser supplying 500mJ per pulse, resulting in an energy density of 3-4 J/cm2.
Harmonic Distortion in Semiconductor Lasers for Analog Transmission
Authors: Morthier Geert
Published: February 2023

The relatively simple concept of analog transmission systems makes them attractive for applications such as fibre-optic distribution of CATV signals and fibre-optic links between central and base stations for wireless telephony. Directly modulated DFB laser diodes are the preferred transmitters for such systems, but the analog character requires a very high linearity of the electro-optic conversion. While the specific requirements depend on the system implementation, CATV systems generally require a small 2nd and 3rd order distortion in a frequency band from 50 MHz to 1.8 GHz. Fibre-optic links for wireless communication on the other hand have the information concentrated in a small bandwidth around e.g. 1.9 GHz and therefore only require a small 3rd order distortion in that band. A 'small' distortion means over 60 dB below the carrier.
Carrier Capture and Escape in InGaAs/InGaAsP Quantum Well Lasers: Effect of Space Charge
Authors: Plyavenek A.G. , Lyubarjikii A.V.
Published: February 2023

Key factors determining the speed of QW lasers are total carrier capture time and the ratio of the capture to escape times [1]. Usually these transport parameters are calculated under flat band conditions [2]. However, the accumulation of positive charge in QW region of InGaAs/InGaAsP lasers gives rise to significant modification of conduction and valence band profiles [3]. In this report we present the results of self-consistent calculations of effective electron capture and escape times in SCH InGaAs/InGaAsP QW laser structures taking into account band bending effects. We show that these lime constants are strongly affected by new intersubband transitions involved in capture processes due to appearance of new bound electron states in the presence of space charge.
Focusing of laser beam with the partial (potential) phase conjugation
Authors: Aksenov V. , Banakh V. , Tikhomirova O.
Published: February 2023

Wave front dislocation arising in the interference optical fields1 have became an independent object under study and indicator of a number wave phenomenon and processes in the nonlinear optics2 and laser physics. Presence of the dislocations is the main obstacle to the phase compensation in the adaptive optics system Moreover, the research branch connected with the use of the dislocations to control the natural media is developing. Dislocation forming has been considered in this paper on the base of solution of the problem of wave phase retrieval from the measurements of intensity distributions I(ρ, z). When the intensity takes zero values the phase of the 3-dimensional field S(ρ, z) has been found to consist of the potential and vortex parts. Each part is due to the potential and vortex components of the Umov-Pointing vector, respectively. The intensity zeros are the discontinuity points (anomaly) for the phase potential part and the centers of spiral dislocations for the phase vortex part.
Effects or frequency down/up conversion competition on ultrashort pulses features in parametric amplification
Authors: Delbarre H. , Przygodzki C. , Boucher D.
Published: February 2023

This work concerns ultrashort pulses (< 100 fs) dynamics in a three wave miring process. Infrared generation via parametric amplification is numerically and analytically analysed in a short type 1 BBO crystal (1 mm) [1]. Generally, pulses temporal recovery in sub-picosccond regime, strongly varies along the crystal due to the group velocity mismatch (GVM) between pulses and lo the short pulse duration.
Self-dispersive spectroscopic sum-frequency generation at an interface
Authors: van der Ham E.W.M. , Vreben Q.H.F. , Eliel E.R.
Published: February 2023

The study of (buried) interfacial monolayers has greatly benefitted from the development of the interface specific nonlinear optical techniques known as IR-visible sum-frequency generation. In particular the ability to probe individual vibrational resonances of the constituent molecules of the monolayer has proven to be extremely valuable. For such studies one often uses a tunable IR source whose bandwidth is narrow compared to the width of the vibrational bands.
2.1μm Master Oscillator Power Amplifier with SBS Wavefront Correction
Authors: Poberaj I. , Zgonik M. , Günler P.
Published: February 2023

Tm,Ho:YAG lasers operating at 2.1 μm are becoming increasingly important finding their way into different applications ranging from medicine to remote sensing and range finding. Much of the interest on the Tm,Ho:YAG lasers was perpetuated by their inherent eye safety. In particular, the safety of the remote sensing and range finding applications can be substantially improved by replacing currently widely used 1.06 μm Nd:YAG lasers which are potentially very harmful to the human eye.
Effect of pump depletion on degenerate four-wave mixing in saturable gain media
Authors: Hung K.M. , Gutiérrez-Castrejón R. , Hall T. J.
Published: February 2023

Co-polarised degenerate four-wave mixing (DFWM), in which all the four interacting beams have the same direction of polarisation, has been utilised to generate high phase conjugate reflectivities (~ 2500) recently [1]. In the co-polarised geometries six gratings are written in the material in which each beam forms a grating with another beam. Several theoretical models have been used to describe this co-polarised DFWM process in gain media [2]-[3]. However, all of them involve the use of small probe approximation and hence not all gratings are present in these models. Moreover, the effect of pump depletion has been neglected. A novel approach using the underlying symmetry is described recently to solve the co-polarised DFWM problem [4]. This approach allows us to take into account the effect of pump depletion, although the two standing gratings between the pumps and between the probe and the conjugate beams are ignored.
Photorefractive Waveguides on Proton-Exchanged Linbo3
Authors: Kostritskii S.M.
Published: February 2023

The detailed experimental investigation indicates that the characteristic feature for all unannealed proton-exchanged (PE) waveguides consists in the absence of the essential photovoltaic (PV) current at light intensities J ≤ 102 W/cm2 which is due to the suppression of the PV-effect up to more than two orders of magnitude. At the same time, based on the data of direct measurements it follows that for this intensity level a marked photorefraction (PR) Δns ~ 0.7 - 2.0.10–5 takes place. Moreover, it is establi­shed that for PE LiNbO3 waveguides electro-optic coefficient r33 is 9 times smaller than for pure LiNbO3, but photoconductivity increases at the PE reaction by from 3 up to 10 times depending on the PE degree -x (Li1-xHxNbO3). Consequently the usual PV-model predicts only Δns < 0.3 10-6 that indicates clearly noneffectiveness of the PV-model for PR description in the PE LiNbO3 waveguides. This disagreement may be explained by the existence of a polarization field contribution in PR because of the photoexcitation of the impurity dipoles appearing in considerable numbers at PE-reaction [1]. In present investigation it is established that the polarization field contribution becomes dominant in PR-response only against the background of the suppressed PV-effect in waveguides with high degree of PE. Therefore, these waveguides are used for formation of dynamic holographic gratings [2]. Note that relatively small value of the Δns in undoped PE waveguides made its application in real devices ineffective. However, the combined proton and copper exchange at low temperature enables to increase the holographic sensitivity by more than three order of magnitude, as concentration of the photoexcitable centres reaches extremely high values (Ccu ≤ 4 at.%) that represent the necessary condition for appearance under light influence of the reversible polarization field with essential value.
Fundamental frequency pulse compression through cascaded second-order processes in type II phase-matched second-harmonic generator
Authors: Dubietis A. , Valiulis G. , Danielius R. , Piskarskas A.
Published: February 2023

Second-harmonic (SH) pulse compression in KDP type II phase matching crystal has been shown to be an attractive method of the pulse shortening, starting with pico- and sub­picosecond pulses from the Nd:glass laser1-3. An inherent feature is that compressed pulses are accompanied by the satellites occurring due to the cascading of second-order processes. It is quite obvious, that if a re-conversion process could be started at proper time, a fundamental frequency pulse, produced by the re-conversion of the SH pulse, may experience a notable shortening. Recently, triggering of the cascaded processes under phase-matching conditions has been shown to be possible by unbalancing of the intensities of o and e-polarized inputs in type II SH generator4.
Nonlinear frequency doubling mirrors as phase shifting elements
Authors: Saltiel S. , Koynov K. , Buchvarov I.
Published: February 2023

Nonlinear frequency doubling mirror (NFDM) that consists crystal for second harmonic (SH) generation and mirror situated behind it (fig.1 - dashed squares) was investigated by us theoretically with respect to the phase and intensity of the reflected fundamental waves. NFDM with nonlinear (NL) crystal at exact phase matched condition was previously used as mode-locking device [1].
Design of Mirror Structures for Two Dimensional Integrated Optical Crosspoint Switches
Authors: Owen M. , Asgari M. , White I.H.
Published: February 2023

There is much interest in monolithically integrated devices to provide compact, robust optical systems. To date Two Dimensional Integrated Optical (2DIO) devices have been designed with mirror structures to manipulate beams in the slab [1,2,3,4]. 2DIO structures provide extremely flexible design advantages over waveguide based devices due to ultra low crosstalk and loss between crossing optical paths. However, the truncation effects of mirror etches and beam divergence have not been analysed in detail. Effects of beam truncation are examined in order to provide methods for designing beam splitters which are required in 2DIO crosspoint switch designs.
Two-photon absorption and optical phase-conjugation in semiconducors n-type ZnSe and n-type ZnSe doped Ag
Authors: Sahraoui B. , Rivoire G. , Bala W.
Published: February 2023

The ZnSe crystals are grown by high-pressure Bridgman method. The samples are cut parallel to (111) crystallographic plane. One of the samples has been annealed at 1100 K in liquid zinc, the other in liquid Zn + 8% Ag . After annealing the samples are mechanically polished and chemically etched[1]. The main of our experiment is to probe the effect of doping on linear (α) and nonlinear (β) absorption coefficients as well on the third order susceptibility χ<3> at 532 nm using picosecond pulses. From nonlinear transmittance we have evaluated two photon absorption coefficient β and we have calculated the imaginary part of χ<3>. Investigating the efficiency (R) of degenerate four wave mixing, we estimated the real part of χ<3>.
Fabrication of Nd3+, Cr3+-codoped YAG ceramics for high - effiency solid-state lasers
Authors: Yoshida K. , Ochi K. , Ikesue A.
Published: February 2023

Nd3+, Cr3+-codoped YAG single crystal fabricated by the Verneuil method was developed by Kiss and Duncan1 in 1964. An energy transfer from the 3d bands (2E state) of the Cr3+ ions to the 4f band (4F3/2 state) of the Nd3+ ions in the YAG was observed for this material, and that doubly doped system operated as a cross-pumped cw laser. In a YAG crystal, Cr3+ ions, as well as Nd3+ ions, play an important role for sensitizing.
New Host Lattices for Optical Hole Burning: Materials of Low Nuclear Spin Densities
Authors: Caprez A. , Meyer P. , Hulliger J.
Published: February 2023

Optical hole burning (OHB) on rare earth ions has so far been performed mainly on single crystals which have been developed as a laser host material. However, an essential drawback of most of these lattices is the high nuclear spin density s of the constituting ions, giving rise to a broadening of the homogeneous width of the absorption of individual rare earth ions [1]. As a result of a limited number of elements providing a high natural abundance of isotopes with zero nuclear spin I or small nuclear momentum µ, there are not too many existing or possible new host lattices to work on. Further restrictions arise in the case of heterogeneous doping as well as from a given site symmetry.
High Quality LiYF4 Laser Host Crystals Grown by Vertical Gradient Freezing
Authors: Rogin P. , Hulliger J.
Published: February 2023

Trivalent lanthanide doped LiYF4 (YLF) is commonly grown by Czochralski pulling [1, 2]. Previous work using the Bridgman technique [3] produced single crystals, however, without control of orientation. Oriented YLF single crystals were recently obtained by a vertical gradient freezing technique based on seeded growth [4]. Both pure YLF and LiY1-xLnxF4 with Ln = Er (0.01 ≤ × ≤ 0.20), Pr (x = 0.01) and Nd (0.01 ≤ × ≤ 0.03) were grown under N2 atmosphere in a glassy carbon crucible. Usable crystal lengths up to more than 50 mm at 15 mm diameter were achieved. Nd and Er doped rods showed IR laser action under flashlamp or NIR laser diode pumping.
Electron Emission From Diamond Films Irradiated By XeCl and KrCl Lasers
Authors: Beloglazov A. , Karabutov A. , Konov V I. , Nassisi V. , Pimenov S.
Published: February 2023

Abstract

A number of diamond films, 0.2 to 4 microns thick, have been grown on Si and Mo substrates by the well-established arc-discharge plasma chemical vapour deposition procedure The photoemission properties of the films were studied according to the technique developed previously for investigations of metal photocathodes. The samples placed in 10-6 Torr vacuum were illuminated by a softly focused either XeCl or KrCl excimer laser beam of 4.02 and 5.6 eV photon energies, respectively. These values are smaller and larger than the gap value of a natural diamond (5.5 eV).
Cavity mode effects in an injection-seeded pulsed optical parametric oscillator
Authors: Haub J. G. , Baxter G. W. , Orr B. J.
Published: February 2023

Narrowband injection seeding can provide continuous tunability and optical bandwidth control in pulsed optical parametric oscillator (OPO) devices suitable for practical spectroscopy. Studies of OPOs based on β-barium borate (BBO) have used either dye lasers1-3 or external-cavity diode lasers (ECDLs)3-5 as seed sources. The injection-seeded OPO cavity can be operated passively, with the cavity length fixed, by slightly misaligning the cavity to reduce its effective finesse.
The potassium niobate OPO and the advantages of tangential phase-matching
Authors: Urschel R. , Borsutzky A. , Rvtz D. , Wallenstein R.
Published: February 2023

Powerful IR radiation tunable in the wavelength range of 1.44-4.05 μm can be generated by an OPO of potassium niobate (KNbO3) pumped by the fundamental of a pulsed Nd:YAG laser 1. The OPO consists of a 10-mm-long AR- coated crystal (critical type-l phase-matching, θ=41°, ϕ=0°) placed in a 12-mm-long flat-flat mirror cavity resonant for the signal wave The energy density at threshold increases from 0.485 J/cm2 at 1.9 μm to more than 0.7 J/cm below 1 48 μm. To avoid damage of the coating of the KNbO3 crystal the pump energy densities should be less than 1 J/cm2. Due to the rather large walk-off of 3.5° the threshold decreases with increasing pump beam diameter (from 0.6 J/cm3 at 2.35 mm to 0.485 J/cm2 at 4,85 mm). Hence, enlarging the pump beam diameter front 3.05 mm to 4.85 mm. the OPO energy and efficiency increases at constant pump energy density (0.975 J/cm2) from 6.4 mJ to 30 mJ and from 9 % to 16.7 %, respectively.
Wide-band and wide-angle nonlinear conversion of signals and images in uniaxial and biaxial crystals
Authors: Zadorozhnii V. I. , Kornienko N. E. , Syteheva A. M. , Konopaltseva L. I.
Published: February 2023

We report on an investigation of widely tunable frequency-response conversion of signals and images based on the three-photon noil-resonant processes of sum- and difference- frequency generation (SFG, DFG) under conditions of noncritical phase-matchings (PM) in a series of uniaxial crystals (e.g., LiIO3, AgGaS2, HgGa2S4, CdSe) aud biaxial ones (e g., KTP, LBO and others). Peculiarities of the conversion process have been analysed in the vicinity of the singular points on the PM surface where double noncriticality of nonlinear processes both in frequency and in the angular divergence of the signal (ω
s
) radiation (the “group center (GC))1,2 or in the angular divergence of the interacting waves (the “tangeutial center” (TC)) are realized.
A Novel Technique for Dye and Ti:Al2O3 Ring Lasers Frequency Locking at Atomic Absorption Lines Using Bi-Directional Injection and Two-Step Pumping
Authors: Slavov D. , Deneva M. , Sloykova E. , Nenchev M. , Barbe R. , Keller J.C.
Published: February 2023

We present (theory, experiment) two original techniques for laser spectral control with high efficiency of the laser frequency locking at the atomic absorption line. Such lasers are of essential interest as sources for optical frequency standards. The first technique employs the competition between the contrapropagated waves in a ring laser in the case of bi-direction injection locking control as shown in Fig. 1. The beam from the narrow-line (~1 pm) injecting laser (dye, Ti:Al
2
O
3
or semiconductor) with intensity 1 is divided into two parts injected through the mirrors M
1
and M
2
respectively in opposite directions in the ring cavity M
1
,M
2
,M
3
. The intensity of the contraclockwise part exceeds substantially (e.g. 0.8 I) this of the clockwise beam to force the laser to operate practically only in contraclockwise direction.
Analysis of light wave scattered by an optically trapped particle
Authors: Uchiyama Toshio , Lai Guanming
Published: February 2023

The laser trapping technique(1) allows one to study a single particle in a noncontact manner and to even manipulate biological particles without giving damage on them if a light of specific optical wavelength is used. In the technique a focused laser beam is necessary to give a trapping force on the particle. The force is calculated by ray tracing for particles from several microns to tens of microns. However, there exists a problem whether it is appropriate to do ray tracing in the range where geometrical optics is no more applicable. On the other hand, light scattered by particle smaller than a micron can be described by Mie theory which is fully based on electromagnetic equations. If the scattering pattern can be obtained, the force on the particle can be determined without ray tracing. So far, scattering patterns by Mie theory has been solved for plane wave illumination. In this paper, we describe a method to calculate the scattering patterns by a convergent beam illumination, which is the case for laser trapping, and applied to study various particles dissolved in liquid using the scattered patterns.Scattering pattern from a spherical particle with plane wave illumination is described by Mie theory, and we can calculate the scattered wave for any specific direction. A focused beam having a wavefront, which could either be given or measured experimentally, can be expanded to a series of plane waves by Fourier transformation. The scattered pattern of each incident plane wave is calculated in a two dimensional array for equal interval of angle or its sine function. The total scattered pattern is vector superposition of these single scattering patterns. Since we observe the back-scattered light in the experiments, the scattered pattern is calculated in the array for equal sine values. The scattering pattern with a convergent beam was calculated by supposing a Gaussian distribution of the wavefront The convergent beam is considered as a combination of various plane waves having different phase and amplitude and the total scattered wave is calculated as the superposition of those plane waves by Mie theory.A Nd:YAG laser is collimated and coupled to the optical microscope through a half transparent mirror. The objective lens with numerical aperture of 0.9 was used to focus the laser beam and therefore traps the particle near its focus. The back-scattered light from the particle passed through the objective and another camera lens was captured by a CCD camera which can be fed into a computer. We found the scattered patterns are dependent on the size and shape of the particle trapped and is quite different to the pattern that Mie theory with plane wave illumination predicts. We found that the pattern calculated with the Gaussian beam assumption for convergent illumination is much closer to the pattern observed in the experiments. We think the scattering pattern can give information on the particle structure as well as trapping force on the particle.
E-symmetry phonon-polariton damping in PbTiO3 perovskite:direct measurement in the time domain
Authors: Gautier C.A. , Ait-Talbi L. , Loulergue J.C. , Etchepare J.
Published: February 2023

An exhaustive study of polariton characteristics is particularly relevant to describe lattice dynamics in polar crystals , especially to address the balance between relaxational and displacive contributions from nuclei in the vicinity of a phase transition.
Stimulated Raman Scattering Processes in H2 by Astigmatic Focusing Geometries
Authors: Perrone M. R. , Piccinno V.
Published: February 2023

The production of multi-wavelengths by stimulated Raman scattering (SRS) in high pressure gases is receiving a great interest in recent years, being the SRS widely used in multiparametric LIDAR systems [1] In particular, the developing of new techniques to control the energy conversion efficiency from the pump radiation to a desired Stokes order represents one of the main research objective pursued in the last years II is well known that by utilising high pressure Raman gas and a low-angle pumping geometry to reduce the four wave mixing processes, a quite high conversion to the first Stokes (Sj) can be obtained. However, as the intensity of S] becomes sufficiently high, it stimulates the second order Stokes (S2) and so on higher order Stokes beams.
Impact of e-beam sustained discharge non-uniformities on CO laser beam quality
Authors: Berdyshev A. V. , Kochetov I. V. , Kurnosov A. K. , Loboyko A. I. , Napartovich A. P. , Sukharev A. G.
Published: February 2023

The cryogenic cw CO laser excited by e-beam sustained discharge has the laser efficiency (30-40)% at the hundred kilowatt level [1]. For a compact laser device of this class a laser gas mixture with densities in the range of 0.5 of the normal one is needed. Then any inhomogeneities in gas density exert strong influence on laser beam quality. Experimental rough estimates [1] gave the laser beam divergence about 0.01 rad at the power 85 kW when using the unstable resonator. A probable origin of a such strong divergence is a spatial distribution of refraction index associated with nonuniform energy release into the gas. A spatial spectrum of index nonuniformities has in general two components: one associated with sizes of discharge volume, and second is due to the small scale turbulence. Setting apart the last problem a two-dimensional semi-analytical model was formulated to describe the effects of nonuniform gas heating in the discharge. The first problem is the large number of physical variables involved: vibrational populations on about 100 levels; charged particle concentrations: gasdynamic variables; laser radiation intensities for about ten vibrational transitions. The second problem is that all these quantities are coupled each to other, and their variations should be described self-consistently. Despite the high productivity of the modem computers, integrating of a full set of equations in 2-D space is still not easy. We have employed the analytical approach to the vibrational kinetics developed earlier: for steady state conditions by Gordiets et al [2], for vibrational evolution in time by Zhdanok et al [3]. Analytical theory allows us to replace 100 vibrational kinetic equations by 3 non-linear equations. Special tests demonstrated a good accuracy of the approximate method (deviation from the numerical calculations using the full kinetic model is as a rule within 10%).
High-Power Coherent and Incoherent UV and VUV Sources
Authors: Tarasenko V.F.
Published: February 2023

Results of the experimental study of exciplex lasers pumped by a radially convergent electron beam and the excilamps based on the longitudinal or the barrier discharges or the volume self-maintained discharge with UV preionization are presented.
Passively Mode-Locked Nd3+:SrLaGa3O7 Laser
Authors: Yumashev K. V. , Prokoshin P. V. , Terentiev A. V. , Mikhailov V. P. , Ryba-Romanowski W. , Golab S. , Pisarski W.
Published: February 2023

In present time the optical and lasing properties of many new Nd3+-doped crystals are investigated to improve the characteristics of neodymium solid-state lasers. The laser action of Nd3+ :SrLaGa3O7 (Nd:SLGO) has been reported in [1]. In this paper we demonstrate for the first lime to our knowledge the passive mode-locking of Nd:SLGO laser. The ultrashort pulses of 25-30 ps duration are obtained. The data of slope efficiency measurements are reported.
Stable Mode-Locked Nd:YAG Laser for Nonlinear Devices Pumping, Providing Precisely Synchronised Optical and Electrical Pulses
Authors: Jacinavicius Saulius , Lukosius Jonas , Michailovas Andrejus
Published: February 2023

Many nonlinear sources of tuneable radiation (optical parametric oscillators/amplifiers, frequency mixers, etc) find their application in variety of optical investigations. To pump them, passively mode-locked lasers are now commonly used. Nonlinear interactions taking place in mentioned devices enormously boost the initial nonstability of pump laser parameters: of pulse duration, energy, spectrum, beam direction and so on. Another problem with passive and passive-active mode—locking technique is that of synchronisation of optical and electrical pulses to trigger experimental apparatus. Eg, ps-resolution streak cameras require pre-trigger pulse preceding by approx. 10÷100 ns the optical signal arriving on entrance slit, and the electrical to optical signal jitter must not exceed 100 ps [1].
Nd:YAG laser caving in Al2O3 ceramic
Authors: Grad Ladislav , Horvat Andrej , Možina Janez
Published: February 2023

In this paper the influences on the dimension accuracy and the roughness of pulsed laser caved shapes in alumina ceramic have been studied. The experiments were performed on the experimental setup shown in figure 1. As a laser source pulsed LP-3000 Nd:YAG laser was used. A single lens, mounted on the z translation stage, with focusing length of 100 mm was used to focus the laser light onto the target surface which was mounted on the x-y computer controlled translation stages. The movement resolution was 10 μm. The samples used were Al2O3 ceramic plates. After treatment ceramic samples were examined by an optical microscope and the surface profile measurement were performed with a stylus apparatus.
Three Field Mixing Processes Enhanced in Large Bandwidths into a Spin Multiplet
Authors: Popescu F.F.
Published: February 2023

Recently we have investigate the resonant enhancement of the three field mixing processes into a soin multiplet [1]. Thus, we have predicted that if one or two among the fields is weak, the maser actions and the parametric processes become decoupleted and it is possible such a resonant enhancement so that although the linear magnetic susceptibily is usual enhanced at a certain frequency, the parametric process is enhanced at the same frequency over the effects of the linear or other nonlinear magnetic susceptibilities.
Growth of Nonlinear and Lasing Optical Thin Films
Authors: Eason Robert W
Published: February 2023

Thin films of optical and nonlinear optical materials form the basis for a wide range of devices such as waveguide lasers, amplifiers, modulators, second harmonic generators and switches. Our work in this area has concentrated on two separate techniques for fabricating thin films, and we describe here our progress to date in controlling both the linear and nonlinear properties of the films, and more specifically, the active dopants that are intentionally included and manipulated during the film growth.
Multifocal Resonator Configurations for Ker-Leus Mode-Locking
Authors: Sorokin E. , MacNamara S. , Sovokina I.T. , Wintner E.
Published: February 2023

Kerr-lens mode-locking (KLM) has become one of the most popular mode-locking schemes employed in ultrafast solid-stale lasers. The incorporation of both gain and mode-locking mechanisms within the active crystal, as in a classical four-mirror X-folded cavity, however, puls contradictory requirements onto the beam parameters inside the active medium. To achieve strong KLM action, the resonator should be close to the instability region, the beam must be lightly focused, and the active medium displaced relative to the beam waist. These requirements have to be traded off in order to achieve good laser action Due to its unique combination of properties, Ti:sapphire remains the only laser medium which offers satisfactory performance in a classical KLM scheme. In order to use KLM with other active media which may possess smaller nonlinearity, gain or damage threshold, or with other pumping schemes, not supporting tight focussing, an alternative scheme is to separate gain and KLM action. The separation of mutually contradicting requirements provides sufficient degrees of freedom, which may be the only way to realize the KLM scheme [1], or at least allow to optimize the results [2]. Although this idea has already been realized experimentally yielding promising results, the lack of comprehensive multifocal resonator analysis did not permit wider usage so far.
Effective Apodized Phase Mask For Optimum FBGs
Authors: Pan J. J. , Zhou F. Q , Shi Y. , Li S. X.
Published: February 2023

FBGs are promising devices for DWDM networks [1]. Phase mask (PM) technique is one of the most versatile techniques for massive production of FBGs. However, ever increasing requirements of DWDM put stringent requirements on FBG sidelobe suppression and spectral skirt sharpness. In this paper, we report a detailed comparison of different apodization profiles with emphasis on narrow linewidth, sharp spectral skirt and a large figure of merit which is the ratio of bandwidth at -0.5 dB to that at -25 dB. Effective apodized PM was fabricated by using e-beam writing and reactive ion-milling (RIM) with stitching error-free. For a gaussian apodized FBG. it has a gaussian refractive index modulation, an inverse gaussian index background and a constant average index change along the FBG with no unwanted dispersion. FBG apodization using PM dithering technique suffers some drawbacks for pulsed UV excimer lasers and for very high UV photosensitive fibers. Scanning writing apodized FBG technique needs double UV exposures for FBG writing and background index change resulting in a lower control accuracy and a lower fabrication efficiency. Using apodization aperture and amplitude masks have the similar problems of double exposure and lower control accuracy resulting unwanted dispersion. Apodized PM technique is an efficient method for qualified DWDM FBGs production with a simple setup and an excellent fabrication repeatability.