bluuebunny/crossref_metadata_2025 huggingface dataset:
All-metal radio frequency excited waveguide carbon dioxide laser
Authors: Mineyev A.P.
Published: February 2023

Transverse radio frequency (rf) gas discharges in the pressure and frequency ranges of respectively 10-150 Torr and 10-150 MHz are being increasingly used in free space and waveguide CO2 lasers, at power levels from a few watts to kilowatts, because of a number of advantages rf excitation has over DC excitation. In the past decade rf excited waveguide CO2 lasers were developed from all-ceramic channel structures to metal-ceramic channel and slab structures.1 Recently, allmetal free space and waveguide structures for rf excited CO2 lasers were presented, in which four walls of the channels were made from aluminium.2,3 We proposed to research a new type of free-space and waveguide lasers in which the square cross-section structure of the discharge channels are formed only by two concave metal surfaces. The metal surfaces also become electrodes in rf discharge.4
Compression of femtosecond light pulses by stimulated Raman scattering
Authors: Jordan C. , Stankov K. A. , Marowsky G. , Canto-Said E. J.
Published: February 2023

Stimulated Raman scattering is an efficient way to shift the frequency of the available laser sources. When the light pulse duration decreases and approaches the transverse relaxation time of the Raman medium, the highly transient interaction reduces the efficiency of the scattering process.1 At the same time, competitive nonlinear processes (selfphase modulation, multiphoton ionisation) limit the conversion into Stokes lines. Nevertheless, by optimised focusing, efficient Raman scattering of ultraviolet femtosecond light pulses was already demonstrated.2 However, the pulse duration in these experiments was not measured and only a rough estimation for the pulsewidth could be done from the spectrum data. Here we report on Raman scattering of visible femtosecond pulses and the first to our knowledge, generation of light pulses below 100 fs using this technique. We show that by proper balancing of the input intensity high efficiency of the Raman scattering for femtosecond light pulses can be achieved. In addition, the Raman-shifted pulses are efficiently compressed 6.5 times as compared to the pump pulse duration.
Kinetic processes in Ar/Xe laser active media
Authors: Soloviev V. R.
Published: February 2023

The lasing on the transitions between the 5d and 6p levels of Xe atoms corresponding to 1.73-3.5-µm wavelengths was obtained in a wide region of pumping power from 10-100 W/cm3 in experiments with nuclear pumping1 to 105 W/ cm3 in experiments with pumping by electron beams.2 There are two main hypotheses about a process of building up the 5d levels of Xe atoms in Ar/Xe mixture. The first one supposes that pumping of 5d levels is a result of dissociative recombination of ArXe+ ion with electron,3 and the second prefers the recombination of

Xe

2
+

(

2

Σ
+

)

ion with electron.1 However, both of these hypotheses fail to describe all the experimental results in the case of low1 and high2 pumping powers. The attempt to take into account the new channel of Xe(5d) building up through dissociative recombination of

Xe

2
+

ion in excited state B2II4 did not solve this problem either. These results lead to the conclusion that the description of variation of plasma composition with changing pumping power is not adequate in all cited kinetic models.
Spatial coherence of XeCl lasers
Authors: Bespalov V. G. , Zhevlakov A. P. , Leschenko D. O. , Yutanova E. Yu.
Published: February 2023

As it is known, excimer lasers have a short time of inversion (order of 10 ns) and high gain because that stimulated emission occurs only at time of several passes on cavity. Let us consider the following model of energetic parameters and spatial coherence forming in flat mirrors cavity. Let us suppose that in initial moment of time the spontaneous emission near output mirror has intensity: where A is amplitude of spontaneous emission on cavity axis, a is the radius of laser cavity aperture, x is transverse coordinate.
Effect of mode nonorthogonality in Fabry-Perot/distributed feedback laser
Authors: Tyszka-Zawadzka A. , Szczepański P. , Woliński W.
Published: February 2023

A fundamental source of quantum noise in laser devices is spontaneous emission from upper level atoms. It is well known that the nonorthogonal nature of the laser modes can enhance a coupling of the spontaneous emission from the active medium to the lasing modes.1,2
Interplay of strain and chemical ordering in GalnP for enhanced laser characteristics
Authors: O'Reilly E. P. , Meney A. T.
Published: February 2023

It is important in semiconductor lasers to match the symmetry of the wavefunctions to the one-dimensional symmetry of the laser beam, with its clearly defined direction and polarisation. It is understood how this can be achieved by the use of built-in strain, but significant effects can also arise due to the chemical ordering of atoms in the crystal during growth. Even stronger effects arise due to the interplay of strain and chemical ordering.
Modulation properties of 3.5µm InAsSb/ InAsSbP cw low threshold diode lasers
Authors: Yakovlev Yu. P. , Imenkov A. N. , Sherstsnev V. V. , Haugholt Karl H.
Published: February 2023

The main application for mid-infrared diode lasers are in high-resolution spectroscopy. Infrared diode laser spectroscopy has earlier been realized by using lead salt lasers.1
The analysis of packaging-induced failure in a cw laser diode
Authors: Yoo J. S. , Lim G. , Kim T.
Published: February 2023

Very recently, there was a report on the packaging-induced failure (PIF) of high power 980-nm laser diodes.1 This phenomenon could be regarded as one of the catastrophic optical degradations (COD). The COD was known to be caused by thermal runway process at the mirror facet.2 The localized heating of the laser facet due to the high nonradiative recombination leads to narrowing of the bandgap, which results in the increase of absorption coefficient. This causes more heating. This positive feedback eventually leads to melting of the facet. But this does not seem to be the case for PIF. In this work, to understand how the pertinent properties of a laser diode are related to the reliability, general safety criteria against catastrophic optical damage were first derived for a laser diode operating under cw condition. Here, all the equations were motivated close to the facet where surface recombination and optical pumping are the dominant mechanisms. This was done by rescaling of carrier diffusion equations and heat conduction equations with the effective width of the photon absorbing region. The safety criteria could be expressed in terms of operating conditions, laser dimensions, and material properties in analytic form.
Analytical solution of phase problem in optics, investigation of configuration and peculiarities of optical interference fields wave pattern
Authors: Aksenov V. P.
Published: February 2023

An accurate analytical solution of the phase retrieval problem s(r) through the intensity distribution I(r) has been obtained in the approximation of parabolic wave equation for a complex amplitude of monochromatic wave field.
Off-plane halo (2-dimensional) laser resonator
Authors: Horváth Z. Gy. , Malyutin A. A. , Kilpio A. V.
Published: February 2023

At the end of the seventies, with the development of the 2-dimensional, planar, so-called "halo lasers," we verified that 1-dimensional radiation is not an inherent property of lasers since it is not a consequence of the physical properties of the lasing process.1,2 In the past 10 years 3-dimensional lasers have also been developed in several laboratories on specially pumped spheres and droplets.3 All of the "non-line-like laser" work has been a nice piece of scientific work, even from the point of view of possible natural cosmic laser processes, but it offered no practical advantages.
Mode-locking of an erbium-doped fiber laser with an InGaAsP laser diode absorber/amplifier
Authors: Kawaguchi Hitoshi , Inoue Jun , Takahashi Yutaka
Published: February 2023

The mode-locking of erbium-doped fiber lasers has recently been the subject of active research and a number of interesting schemes have been reported. For example, a traveling wave InGaAsP laser diode (LD) amplifier was used as an intracavity modulator.1 An LD was simultaneously used as a pump source, an intracavity phase modulator, and an étalon.2 Passive mode-locking using multiple quantum well saturable absorber was also reported.3,4
Stable laser resonators with inhomogeneous mirrors
Authors: Troitski Y. V.
Published: February 2023

Coordinate-dependent mirrors in stableresonator lasers were used by us for: (1) obtaining transverse intensity distribution (TID) with predetermined non-Gaussian profile, without substantial decrease of power in comparison with the laser having ordinary homogeneous mirrors; (2) control of a mode structure of intraresonator field; and (3) obtaining the minimal diffraction-limited divergence output beam from a laser with large-volume active medium. Mirrors with a graded phase of reflection are sometimes needed, e.g., in the problem of transverse mode selection. But in most cases mirrors with graded amplitude of reflection are needed. For the latter case, reflection phase must be constant over the whole mirror surface that looks at active medium, otherwise diffraction losses became intolerable. Besides that, it is important to decrease the diffraction from narrow border areas between two parts of the mirror that have unequal reflectances. Methods for producing dielectric multilayer low-loss mirrors with various functions R(x, y) are described. Each mirror consists of 2 or 3 structures deposited successively. One structure has the thickness h(x, y) depending on coordinates. If two-grade mirror was needed, the inhomogeneous structure was deposited in the presence of thin plastic-film mask, electrostatically held on the substrate. Continuous variation h(x,y) was achieved by means of half-shadow deposition through a system of screens with calibrated holes. Formulas for the case of two screens with circular holes are suggested and confirmed experimentally.
Multiwaveguide CO2 laser with diffractive coupled channels
Authors: Abramski K. M. , Plinski E. E , Witkowski J. , Nowicki R.
Published: February 2023

The constructions of high power RF excited waveguide lasers based on multichannel arrays usually require investigations of the cross-coupling between the laser beams in the array.1,2 We built two structures of a ten-channel RF excited CO2 waveguide laser array. Each laser was 400 mm long (380 mm of active length) with the cross-section of 2.2 × 2.2 mm of an individual channel and 0.5 mm thick sidewalls. The first structure was an uncoupled array whereas the second one was diffractive coupled. The maximum output power of the uncoupled array was 250 W at the pressure of 105 Torr. We applied a simple and useful optical arrangement with an external diffraction grating (153 lines/mm) for the simultaneous observation of an array laser spectrum. The laser beams spread on the grating were observed as a dot matrix at a phosphor image screen in a re-imaged near field. Manual and 2-D PZT mirror tuning and tilting enabled us to align all laser beams into the same matrix row corresponding to the separate spectral line. The lasers in the array operated at the few strongest P- or R-branch transitions of the 10.4µm band. A pattern of the transitions was easily identified by above arrangement.
Amplitude and frequency stability of an injection-locked diode-pumped miniature Nd:YAG ring laser oscillating at high output power
Authors: Freitag I. , Tünnermann A. , Welling H.
Published: February 2023

Diode-pumped miniature ring lasers1,2 are known as reliable sources of stable single-frequency radiation. Due to their low amplitude noise and high inherent frequency stability they are well suited for high resolution spectroscopy and interferometer-based metrology. An especially high resolution is required for the detection of gravitational waves using Michelson type interferometers. For these systems, a light source with high continuous wave output power in single-frequency operation, excellent frequency stability and extremely low amplitude noise as close to the quantum noise limit as possible is essential. Based on a miniature Nd:YAG ring laser,2 a light source has been developed that has the potential to meet these requirements.3 By injection locking a high power diode-pumped rod laser to a miniature ring laser, a singlefrequency output power of 18 W has been demonstrated. Since the locking range scales with the power ratio of master and slave laser, a high output power of the master laser is desirable for reliable performance. This contribution reports on the substantial progress in power scaling of miniature ring lasers.
Advanced solid-state passive shutters based on Cr4+-doped Mg2SiO4 and Y2SiO5 crystals
Authors: Mikhailov V. P. , Zhavoronkov N. I. , Kuleshov N. V. , Avtukh A. C. , Shcherbitsky V. G. , Minkov B. I.
Published: February 2023

It is known that Cr4+-doped laser crystals, such as Mg2SiO4, Y3A15O12, and Y2SiO5, have beautiful lasing characteristics.1,2,3 However in our opinion, the nonlinear properties of Cr4+-doped materials are very important too, because they allow creation of suitable devices for quantum electronics such as passive Q-switchers.2,4
Passive semiconductor shutters for infrared Er and Ho lasers
Authors: Lukashev A. , Chernikov A. , Kozhukhov A.
Published: February 2023

Bleaching properties of epi-layers of InxGa1-xAs compound with variable x on different substrates were tested with regard to their possible use as passive shutters for Er-glass (λ = 1.54µm) Ho (λ = 2.1µm) and Er (λ = 2.79-2.94µm) lasers. Passive Q-switching in Ho and Er lasers was achieved. Operation and limitations of using of these shutters in flashlamp and diode-pump IR solid-state lasers are discussed.
Small-size solid-state holographic distributed feedback laser
Authors: Efendiev T. Sh. , Katarkevich V. M. , Rubinov A. N. , Ryzhechkin S. A.
Published: February 2023

In dye lasers with light-induced distributed feedback (DFB) liquid solutions are typically used as active media. The intrinsic fault of such lasers is the high sensitivity of laser wavelength to temperature.
Periodic FTIR Q-switching of Ti:sapphire laser with flash-lamp pumping
Authors: Bratus A. L. , Lukyanov A. L. , Khomenko S. I. , Chernyshev A. V.
Published: February 2023

The most important problem in application of tunable Ti:sapphire lasers is the possibility of operating the temporal and spectral parameters of output radiation. The generation both of giant pulses and pulse-periodic sequence of laser pulses is of interest for some practical tasks.
Crystalline passive Q-switching of 1.3-µm Nd-lasers and Raman shifting to eye-safe region
Authors: Basiev T. T. , Sigachev V. B. , Doroshenko M. E. , Zverev P. G. , Osiko V. V. , Prokhorov A. M.
Published: February 2023

Stimulated Raman scattering (SRS) of 1.3-µm radiation of Nd-lasers can be used to obtain radiation in eye-safe spectral region. For this purpose it is necessary to have an appropriate pump laser operating in Q-switched mode and active medium for SRS. The simplest and most reliable Q-switching of Nd-lasers at 1.3-µm wavelength can be realized by using crystalline saturable absorbers (SA). Nowadays only a limited number of dielectric crystals, which possess nonlinear saturable absorption in the desired region, are known. In this paper we report on a study of Q-switching mode of operation of 1.3-µm Nd-lasers with the Nd2+:SrF2 and V3+:YAG crystalline SA, and Raman shifting of this laser wavelength in Ba(NO3)2 crystal to eye-safe spectral region.
Dynamics features in a model of additive pulse mode-locked laser
Authors: Melnikov L. A.
Published: February 2023

Additive-pulse mode-locking (APM) leads to the generation of stable ultrashort pulses in a wide variety of solid-state lasers. There has thus been considerable interest in the mechanisms responsible for APM. Theoretical treatments based on the model of interferential reduction of a width of pulse with a given profile owing to a reflection from nonlinear coupled cavity commonly give the estimations of the stable locking interval of cavity mismatch.1,2 Recently, more complicated dynamics were observed; for example, the THz beating signal with frequency inversely proportional to the length mismatch,3 period doubling and chaos in pulse train at high value of nonlinear phase shift in coupled cavity.4 In this paper the results of numerical simulations of different dynamics of APM laser with use of a full set of laser equations5 are presented.
Population mechanisms of the roomtemperature 551 nm Er:LiYF4 laser
Authors: Pollnau M. , Heumann E. , Heine F. , Danger T. , Lüthy W. , Huber G. , Weber H. P.
Published: February 2023

One of the interests in solid-state laser physics has focused on diode-pumped blue and green upconversion lasers. At 551 nm upconversion-pumped laser operation in Er3+:LiYF4 at cryogenic temperatures has been reported, see e.g., Ref. 1. Recently room-temperature lasing under different excitation schemes has been achieved.2,3 However, the population and deexcitation processes of the upper laser level as well as the influence of reabsorption on the laser wavelength4 have not yet been quantitatively understood. In this paper the results of a computer simulation of the Er3+:LiYF4 laser are reported. The rate-equation scheme considers all excited levels up to 2H9/2, ground-state depletion, excited-state absorption (ESA) on the pump and laser wavelength, three upconversion processes, stimulated emission, and a realistic resonator design. From the computer simulation the population mechanisms of the laser system are analyzed and suggestions for a better laser performance are derived.
Spectrum stabilizing in Cr:Tm:Er:YAG laser at 2.69µm
Authors: Mochalov I. V. , Petrovskii G. T. , Sandulenko A. V. , Sandulenko V. A. , Terpugov V. S.
Published: February 2023

It is of much difficulty to provide efficient lasing on YAG:Er3+ crystal at the shorter wavelength transition (2.69 µm) of the 3µm-lasing spectrum of Er3+ due to high value of

I

13
/
2

4

level lifetime and because of cross-relaxation. Codoping the crystal with Cr3+ ions as sensitizers and Tm3+ ions disactivating 4I13/2 level, situation changes. However the tendency of Cr: Tm:Er:YAG (CTE-YAG) laser spectrum to longer wave shifting still remains. In this work, the possibilities of stabilizing the STE-YAG lasing spectrum have been studied by the experimental and calculating methods. The method of evaluating the excitation energy transfer efficiency is suggested.
Spectroscopic investigation of the visible and infrared emission in Tm,Ho-doped YAG and YLF crystals
Authors: Falconieri M. , Lanzi A. , Salvetti G. , Toncelli A.
Published: February 2023

Thulium-sensitized holmium lasers have proved to be very attractive, efficient infrared radiation sources in eye-safe spectral regions. Following to Tm 3H4 excitation of interest for optical pumping with commercially available diode-laser, transfer of energy to the Ho 5I7 upper laser level competes with a variety of interactions that may cause energy loss. The relative importance of the various processes is not very often considered, and still needs to be carefully analyzed. In this paper we describe our results of spectroscopic measurements carried out after Tm 3H4 excitation, in order to identify and evaluate the main de-excitation mechanisms.
CulnSSe-doped glass saturable absorbers for the passive mode-locking of neodymium lasers
Authors: Yumashev K. V. , Mikhailov V. P. , Prokoshin P. V. , Jmako S. P. , Bodnar I. V.
Published: February 2023

In this letter we report on CulnSSe-doped glasses used as a saturable absorber for passive mode-locking of a Nd:YAG and Nd:YAlO3 lasers. Ultrashort pulses of 16 ps duration with 20 µj of energy (for YAlO3 at 1.08µm), and 36 ps duration with 45µj of energy (for YAG at 1.064µm) are achieved, respectively. The bleaching relaxation time of CuInSSe-doped glass saturable absorber is found to be ~11 ps. The optical damage threshold for CuInSSe-doped glasses estimated from the intensity dependent transmittance measurement with the use of laser pulses of 15 ps duration was ~20 GW/cm2.
Spectroscopic properties of tetrahedrally coordinated centers for new solid-state laser materials
Authors: Moncorgé R. , Manaa H. , Boulon G.
Published: February 2023

This paper gives the state of the art of the optical and laser properties of what is now interpreted as Cr4+ and Mn5* active centers in crystals. The comparison of these properties shows up the similarities of these systems but also what distinguishes them. This description is analysed within the framework of the strong-field model and the ionic crystalline environment approximation. A discussion is then developed and shows the limits of this description, what justifies and remains puzzling in the present interpretation and what needs to be studied further.
Two types of emitting centers in Cr-doped Y2SiO5 laser crystals
Authors: Kuleshov N. V. , Mikhailov V. P. , Shcherbitsky V. G. , Minkov B. I. , Glynn T. J.
Published: February 2023

Chromium-doped forsterite and YAG have been shown to be efficient laser materials for the near-infrared. The lasing centers were described as Cr4+ ions occupying tetrahedrally coordinated positions. Recently, laser action in Cr4+:Y2SiO5 was demonstrated at low temperatures1 and at room temperature.2 One of the most interesting features of this new laser material is the dependence of output spectra on the pump wavelength.1 Moreover, luminescence properties of the Cr: Y2SiO5 were studied in Refs. 3 and 4, but the origin of the second emission, clearly observed at low temperatures, was not determined. In this paper we discuss the spectroscopic properties of tetravalent chromium in two silicates Y2SiO5 (YSO) and Gd2SiO5 (GSO). The results of polarized optical absorption, emission, and lifetime measurements are presented.
Pr3+-doped silicates as potential visible laser materials
Authors: Mikhailov V. P. , Kuleshov N. V. , Radkevich S. A. , Minkov B. I.
Published: February 2023

The interest in solid-state lasers based on Pr3+ is due to the fact that Pr3+ offers many transitions in the visible and nearinfrared spectral region.1 We studied for the first time to our knowledge the optical absorption and fluorescence of Pr3+: Y2SiO5. The Stark level diagram was obtained and interpretation of the optical transitions was made.
Mode-locking of a Pr3+-doped fibre laser by pump pulse induced cross phase modulation
Authors: Peter D. S. , Onishchukov G. , Hodel W. , Weber H. P.
Published: February 2023

We report for the first time on a synchronously pumped mode-locked praseo-dymium-doped fluoride fibre laser emitting at~1.3µm. Mode-locking is achieved by a periodic phase modulation, which results from cross-phase modulation induced by the pump–pulses in the active fibre. The pump source used in the experiments is a Nd:YAG laser generating 90 ps pulses at a repetition rate of 82 MHz. The fibre laser cavity length is matched to a multiple of the pump laser cavity length (9 times). The active fibre is an 8-m-long praseodymum-doped ZBLAN fibre with a dopant concentration of 1000 ppm, a core diameter of 4.8 pm, and a cutoff wavelength of~1µm. The absorption at 1064 nm is approximately 0.2 dB/m. The fibre laser typically reaches threshold for ~400 mW of coupled pump power. Despite the fact that the fibre laser is pumped in the extreme long-wavelength wing of the absorption band, a cw output power of 20 mW is obtained for a coupled pump power of ~1 W. Because of the strong (normal) group velocity dispersion at 1.3 pm in the praseodymium-doped fibre, the generated pulses are far from bandwidth limited, when no dispersion compensating elements are used in the cavity. However, the spectral width of these pulses is ~1.2 nm, which shows that pulse durations in the ps range can be obtained using dispersion compensation. Details of the cw and the modelocking characteristics of the fibre laser are presented. The method of modelocking by cross-phase modulation is compared with other mode-locking techniques such as loss modulation using an acousto-optic modulator.
Efficient white ion laser with internal separation of gases in the open-flow discharge
Authors: Yeremenko T. Yu. , Babin S. A. , Kondratenko M. A.
Published: February 2023

High-power white lasers have a lot of scientific and technical applications. Usually they are represented by ion lasers with argon-krypton mixture because they have a set of the strongest laser lines suitable for these purposes (488, 514 nm – Ar+ and 647 nm – Kr+). The efficiency of gas-mix lasers is substantially lower (by a factor of 3-4) than in pure gas lasers. The general reason is different influence of discharge on axial and radial distributions of each plasma component. This and some other phenomena (e.g., difference in ionization energies) don't permit achievement of optimal generation conditions for each gas in the entire volume of active medium. Besides, the electron temperature of argon plasma drops as krypton is added. To solve some of the problems opportunities of open-flow discharge have been applied.
An angular divergence of output beams in planar gas lasers
Authors: Kuznetsov A. A. , Ochkin V. N. , Udalov Yu. B. , Witteman W. J.
Published: February 2023

Molecular gas lasers based on a planar discharge geometry are currently of great interest because of their high specific output power.1 However, when strong requirements on spatial characteristics and mode quality of the laser output are imposed there are certain difficulties in a planar resonator design.2-3
Low jitter (<1 ps) passively mode-locked fibre soliton laser
Authors: Gray S. , Grudinin A. B. , Loh W. H. , Payne D. N.
Published: February 2023

Passively mode-locked fibre soliton lasers have become attractive as sources for laboratory and telecommunications applications due to their properties of simplicity, tunability, and subpicosecond operation. However, such lasers tend to suffer from instability in the repetition rate, which for many applications is unacceptable. Recently, though, stable harmonic passive mode-locking was observed in a ring laser configuration.1 In this paper, we present a detailed experimental study of time jitter in such a laser and demonstrate that a jitter as low as 600 fs can be obtained.
Novel light-polarizing reflectors for internal-mirror gas laser
Authors: Bel'tyugov Vladimir N. , Protsenko Sergei G. , Troitski Yuri V.
Published: February 2023

Most of the serial internal-mirror gas lasers have nonpolarized output radiation. Such a fact causes an amplitude unstability and loss of energy if an optical scheme with a laser designed for a determined polarization. Polarizers, inserted into a laser resonator (Brewster plates, prisms, etc.), complicate its construction and increase losses. Laser resonator design is significantly simplified by the use of laser mirrors having a noticeable polarization anisotropy of reflectance for two orthogonal polarizations.
Characteristics of a cw multiline He-Cd+ laser with transverse radio frequency excitation
Authors: Reich N. , Mentel J. , Mizeraczyk J.
Published: February 2023

It is known since many years that with a capacitively coupled transverse radio frequency (ccrf) discharge the same blue (441.6 nm), green (533.7 nm and 537.8 nm), and red (635.5 nm and 636 nm) lines can be excited in a He-Cd+ mixture as with a hollow cathode discharge. However, so far a quantitative specification of this laser is missing. Therefore it will be given here at least in parts. The discharge was operated between 400-mm-long and 4-mm-wide electrodes in a ceramic alumina oxide tube of 4 mm inner diameter and 400 mm length that was inserted into a fused silica tube ended off in Brewster windows. The Cd vapor was fed into the tube by an oven attached to the fused silica tube half way between the windows. A nearly homogeneous, controllable Cd vapor distribution could be achieved within the A12O3 tube by this method. The discharge was maintained by a rf generator operating at 13.56 MHz with an output power up to 400 W. To obtain a uniform discharge between the two electrodes a special matching was used which symmetrizes the rf voltage.
Electron-beam conditioning for free-electron lasers and masers
Authors: Zhang S. C. , Elgin J. N.
Published: February 2023

Both theoretical and experimental investigations have indicated that the spread of the electron beam (e-beam) limits the operating wavelength, gain, and efficiency of the free-electron lasers and masers. Recently, several authors proposed methods of e-beam conditioning.1-3 Here we present a novel method of conditioning the e-beam by using a tapered, reversed axial guide magnetic field. The results of nonlinear 3-D simulation have confirmed our proposal. In the simulation we consider a solid e-beam having radius Rb = 0.25 cm, energy Eb = 750 keV, and current Ib = 300 A in a cylindrical waveguide with radius Rw = 0.51 cm, where an axial guide field Bz and 3-D wiggler with amplitude Bw and period lw = 3.18 cm govern the electrons and 5000 electrons with the initial state of Gaussian random distribution are tested.
Investigation of a nitrogen laser excited by sliding discharges
Authors: Grozdanov K. A. , Atanasov P. A.
Published: February 2023

Sliding discharges or lasers along the surface of a dielectric has many applications as preioniser, plasma electrode, and direct excitation source.1-3 In this paper we report on a study of a simple N2 laser employing single or twin sliding discharges for direct excitation. The addition of SF6 is found to improve laser performance. The polarity of the applied voltage is of great importance for the output characteristics of the sliding discharge lasers.
High-power picosecond pulse generation in multicontact diode lasers using modified Q-switching techniques
Authors: White I. H. , Williams K. A. , Hughes D. M. , Burns D. , Sibbett W.
Published: February 2023

There is currently much interest in high power picosecond pulsing techniques at Gigahertz repetition rates in diode lasers. However, many of the potential applications in, for example, communications and optical signal processing, place stringent demands on the timing jitter of the optical pulse train generated and hence increasingly research interest has been concentrated on achieving high-quality pulses.
Passive mode-locking of Bow-Tie lasers
Authors: Williams K. A. , White I. H. , Laughton F. R. , Sarma J. , Penty R. V. , Middlemast I. , Ryan T. , Roberts J. S.
Published: February 2023

High-energy compact picosecond pulse sources are required for applications as varied as LIDAR, free space communications, spectroscopy, and the pumping of nonlinear optical systems. Bow-Tie diode lasers offer an economic source for higher power, spatially monomode light, overcoming many of the limitations that are imposed by gain saturation in conventional narrow stripe lasers.1 Under Q-switched operation, for example, record 100 pJ, 15 ps pulses have already been generated.2
Multiple colliding pulse mode-locking in a semiconductor laser: experiment and theory
Authors: Martins-Filho J. F. , Avrutin E. , Ironside C. N.
Published: February 2023

We present a modified monolithic passive colliding pulse mode-locked (CPM) laser configuration, which can generate 2, 3, or 4 pulses in the cavity, giving the second, third, or fourth harmonic of the repetition rate. The laser has a contiguously electrically connected gain section and 3 separated sections placed at every quarter of the cavity length. Its operation can be switched between 2, 3, or 4 pulses depending on the bias (forward or reverse) applied to each of its 3 independent sections, changing the position and number of saturable absorbers in the cavity. The laser is a stripe loaded waveguide fabricated on a 4 quantum well GaAs/ AlGaAs material. Its structure and the fabrication procedure are similar to the CPM laser described in Ref. 1. The total length of the laser is 600 µm and each one of its 3 independent sections is 30 pm long. It generates 120, 180, or 240-GHz repetition rate. Figure 1 shows the cross-correlation interferogram2 for 4 pulse operation, where we measure 1.2-ps pulse width at 240-GHz repetition rate. Figure 2 shows the optical spectra for the same configuration. The time bandwidth product is 0.35. This is the first observation of multiple CPM laser operation.
Third-order nonlinear optical properties of Au-particles/SiO2 glass composite thin films prepared by sputtering method
Authors: Tanahashi I. , Yoshida M. , Manabe Y. , Mitsuyu T. , Sasaki S. , Tokizaki T. , Nakamura A.
Published: February 2023

Small metal particles embedded in glasses have attracted much interest as materials for all optical functional devices, such as optical switches, shutters, or waveguides.1 Although the large nonlinearity and the fast time response are expected for such materials, the value of the third-order nonlinear susceptibility, χ(3), of these glasses was at the range of 10–13-10–11 esu because of the low solubility of Au into glasses.2 To resolve this problem, we have tried to prepare Au-particles/SiO2 glass composite thin films (Au/SiO2 films) with higher Au concentrations using a sputtering method. We could obtain the larger χ(3) values of 10–7-10–9 esu at the surface plasmon resonance of Au particles.
Laser pulse compressor utilizing stimulated Brillouin scattering and laser induced plasma switching
Authors: Franck J. B. , Riede W.
Published: February 2023

One fundamental problem with current laser sources is that while the mechanisms that produce amplification by stimulated emission may be modified by a variety of means to produce laser pulses of different pulse lengths, this is of course specific to the laser in question, and in most cases there is an upper and lower limit that may be achieved. The upper limit to pulse length is for several laser sources continuous wave (CW) operation. The lower limit is often determined by the stability of the lasing state and several other factors, such as pumping scheme, Q-switching, etc. However, as is most often the case, if a specific pulse length is desired, a specific configuration of the laser system may be developed to meet that need. Then normally only the desired pulse length can be obtained. Nonlinear pulse shortening (NLPS) was discovered in the early 1970s and has been discussed by various workers.1–3 This technique utilizes the property of stimulated Brillouin scattering (SBS) and/or stimulated Raman scattering (SRS) to shorten pulses. Pulse lengths in the 100-psec region at 2 mJ per pulse have been created utilizing SBS and 1 psec utilizing SRS, which produces a rather large wavelength shift. These processes have been shown to be successful for a variety of laser systems operating at a variety of wavelengths. In this paper we discuss a method specifically using a Nd:YAG laser which is operating at wavelengths in the vicinity of 1.06 μm.
Fabrication of vertical light couplers in polymeric waveguides by embossing
Authors: De Dobbelaere P. , Israel D. , Van Daele P. , Baets R. , Möhlmann Gustaaf R. , Horsthuis Winfried H. G.
Published: February 2023

The combination of vertical optical taps with planar optical waveguides could improve the functionality of guided wave devices for a number of reasons: (a) They permit three-dimensional optical interconnection between different layers or boards. This offers a considerable improvement of the processing capabilities of information systems, (b) Such structures are very interesting for applications such as OSM (optical surface mount)1 and OBPI (optical backplane interconnect). In these applications light is tapped from the waveguide into a functional component or board; after processing, new light signals are injected into the waveguides. The functional component can be a single optical device (optical isolator, optical amplifier, optical modulator, etc.), a single opto-electronic device (laser diode, detector), or an opto-electronic system consisting of opto-electronic transducers and electronic processors (receiver-transmitter module, OBPI, etc.).
The thin-film laser-active quasi-waveguide as a new type of radiating system
Authors: Bagdasaryan H. V. , Meliksetyan T. E. , Sargsyan G. R.
Published: February 2023

The thin-film active quasi-waveguide (Fig. 1) is a system which consists of a thin (up to several dozen wavelengths) active layer inserted between two passive dielectric media with refractive indexes higher than those of the active medium. Therefore this system has only leaky modes. In the active quasi-waveguide the role of mirrors of the ordinary resonator is carried out by the boundaries of the active layer with the coefficient of reflection determined by Fresnel's formulae. The order of interference determines the modes of quasi-waveguide radiation analogous to transverse modes of an ordinary laser. Each wavelength in modes is being radiated under a different angle; that is, the quasi-waveguide is an active dispersion system, which permits the generation wavelength to be tuned smoothly by turning only the external mirrors. The possibility of light generation in active quasi-waveguide is investigated in Ref. 1. We have realized a double-frequency quasi-waveguide laser with independent frequency tuning in spatially separated laser beams using two external mirrors. Another important application of the quasi-waveguide is its operation as a thin-film amplifier. In this case radiation with divergence close to diffraction divergence was obtained for incident signal of arbitrary divergence. The signal was injected into the quasi­waveguide system both below and above threshold.
An accurate large-signal dynamic model of distributed-feedback semiconductor lasers
Authors: Wang X. , Blondel M.
Published: February 2023

An accurate modelling of distributed feedback (DFB) lasers is useful in order to physically understand their behavior, as well as to provide guidance for the design of their structure. Models of the static and small-signal characteristics of DFB lasers are already available. However, their large-signal dynamic model is still a developing subject. Two models can be used for this purpose now, which include the power transfer matrix model and the transmission-line laser model.1
High power cw mode-locked optical parametric oscillator of KTP
Authors: Grässer Ch. , Wang D. , Beigang R. , Wallenstein R.
Published: February 2023

Optical parametric oscillators (OPOs) are powerful, reliable light sources for the generation of tunable light pulses in the spectral range from the visible to the near infrared. In particular, cw mode-locked systems that are synchronously pumped by a mode-locked pump source can produce in this spectral range tunable pico­second and sub-picosecond pulses at high repetition rates. For many applications, however, the broad bandwidth connected with picosecond and sub-pi­cosecond pulses does not provide sufficient spectral resolution.1 For this reason pulse lengths of 15 to 20 ps should be a good compromise between short pulse duration and a spectral resolution of at least 1 cm−1.
Scanning of an injection seeded BBO optical parametric oscillator
Authors: Boon-Engering J. M. , van der Veer W. E. , Hogervorst W.
Published: February 2023

In this contribution we present a β-BaB2O4 optical parametric oscillator (OPO) that is pumped at 355 nm by a Q-switched single-axial mode pulsed Nd: YAG laser. The OPO, operated in a ring-cavity configuration, is injection seeded by a low power diode laser at 830 nm. The results of the injection seeding indicate a narrow-bandwidth output of the OPO at the signal (620 nm) and idler (830 nm) wavelengths. To stabilize the length of the OPO cavity, a Hänsch-Couillaud1 locking mechanism is incorporated: the continuous light from the diode laser transmitted through the OPO cavity is used to optimize the cavity length. This stabilization technique is also used to sta­bilize external cavities in continuous laser systems.2 The idler output of the OPO follows the same optical path as the diode laser (Fig. 1). To prevent disturbance of the locking mechanism by the idler light pulses, a chopper was placed in front of the lock box. With this scheme we are able to tune the seeded OPO, while keeping the cavity length optimized.
Particle densities in copper ion lasers with helical cathodes of different transparency
Authors: Grozeva M. , Sabotinov N.
Published: February 2023

Previous studies of helical cathode He-Cu and Ne-Cu lasers show that an increased transparency of the helix results in both higher gain on laser lines and higher laser output power.1–3 To optimize laser operation, information about the dependence of different discharge parameters upon helix transparency and their influence upon metal atom, metal ion, and buffer gas ion densities is necessary.
Rare gases used in a copper vapor laser: qualification of physical phenomena
Authors: Goosssens J.-P. , Le Guyadec E. , Lemaire P. , Valrho C. E.
Published: February 2023

Effects of rare gases, used as buffer gas in longitudinal discharge copper vapor laser, on the output power is not completely explained. Negative effects for any other rare gas than neon are commonly found.1,2 We present the effects of rare gases for two different lasers: 40 and 80 mm of inner tube diameter. The use of powerful diagnostics: time resolved electron density measured from Stark effect,3 time resolved spectral intensities of lines from copper and the buffer gase, optical power, deposited power in the laser tube, pyrometric data…, allowed us to explain the positive or negative effects on the power with He, Ne, Ar, Xe, or a mixture of them.
Low voltage vertical-cavity surface-emitting lasers with low resistance GaAs/AlAs mirrors using δ-doped transition layers
Authors: Paraskevopoulos A. , Künzel H. , Sebastian J. , Gramlich S. , Hey R. , Jenichen B. , Böttcher J.
Published: February 2023

A low series resistance is a prerequisite for achieving acceptable performance of a vertical-cavity, surface-emitting laser (VCSEL). For laser emission at λ = 900–1000 nm, the binary GaAs/AlAs combination provides the adequate material choice for the distributed Bragg reflectors (DBRs), considering the difference in refractive index and the thermal conductivity. In this case, however, the potential barriers at the heterointerfaces seriously impeded the current flow and lead to high series resistance, particularly in the p-type doped DBR structures.
Output characteristics of AlCaAs-DH and InGaAs-QW vertical-cavity surface-emitting lasers under strong cavity resonance detuning
Authors: Gmachl C. , Köck A. , Golshani A. , Gornik E. , Rosenberger M. , Walker J. F.
Published: February 2023

Vertical-cavity surface-emitting lasers (VCSELs) become increasingly important to optical fiber and free-space communication. Still the actual device offers a wide scope for research on its fundamental properties as well as for device optimization.
Phase locking of vertical-cavity surface-emitting semiconductor lasers by external light injection
Authors: Li Hua , Lucas Timothy L. , McInerney John G.
Published: February 2023

Vertical-cavity surface-emitting semiconductor laser's (VCSEL) have very short cavity lengths (~μm), which usually result in single longitudinal mode operation. However, their transverse mode spectra are often complicated and their spectral linewidths correspondingly broad. Here we consider how to control transverse mode spectra and linewidths by weak optical injection from an external coherent source.
Preparation of gratings with alternating dipole orientation in nonlinear optical polymers by means of photothermal poling
Authors: Yilmaz S. , Bauer S. , Gerhard-Multhaupt R.
Published: February 2023

Polymers with nonlinear optical chromophores1 as guest molecules or side groups are of fundamental as well as practical interest. Macroscopic nonlinear optical properties are only found if the centrosymmetry in these glassy polymers is broken by means of a suitable dipole-orientation process. For sufficient stability, the dipole orientation must be frozen in by keeping the polymer at temperatures well below its glass-rubber transition. Usually, the dipoles are first oriented by means of poling in a strong electric field above the glass-transition temperature of the polymer and then locked in their angular positions during slow cooling. For poling selected areas only, patterned electrodes2 must be used in that case because of the global heating.
The use of laser fluorometry for diagnostics of sea phytoplankton pigments
Authors: Chernyavskaya E. A.
Published: February 2023

Environmental problems and, in particular, the diagnostics of sea phytoplankton pigments, are very important now.
Short pulse excitation in waveguides with nonlinear distributed couplers
Authors: Fick J. , Vitrant G.
Published: February 2023

Different techniques are possible to excite optical waves in waveguides. Distributed couplers are generally used for the excitation in a planar waveguide where prism and grating constitute the two major alternatives. However, but-coupling is widely used for channel waveguides although it requires nice surfaces which can be difficult to realize in some soft materials. In addition the coupling efficiency can be strongly limited by the overlap integral between the incident beam profile and the guided mode. Distributed couplers are an interesting alternative in this case, when associated with an integrated focusing component, for instance a taper or a curved grating. Then, the coupling efficiency in the channel waveguide is essentially limited by input coupler efficiency which can be very high in the case of a grating with a special profile.
Improvement the output beam parameters of excimer, copper-vapor, CO2, and solid-state lasers by methods of adaptive optics
Authors: Kudryashov A. V. , Panchenko V. Ya.
Published: February 2023

The application of lasers in technological processes and medicine needs the creation of special systems of control and formation of given radiation characteristics on the developed object. Such tasks could be solved by use of elements and methods of adaptive optics.
Laser monitoring of aerosol pollution of air basin of industrial centers
Authors: Balin Yu. S. , Razenkov I. A.
Published: February 2023

The information presented in this paper describes the lidar potentialities and the problems that arise in lidar application to ecological monitoring of the urban air basin. The LOZA-3 lidar is used for monitoring the spatio-temporal structure and dynamics of aerosol contamination spreading. This lidar accomplishes two modes of operation. The first one accomplishes in the manual scanning regime in which displacement of a sounded object cannot be predicted and must be followed using a TV scanning system.
Possibilities of dynamical spectroscopy for diagnostics of cardiovascular diseases
Authors: Korolevich A. N. , Khairullina A. Ya.
Published: February 2023

All diseases are known to lead to changes not only in blood biochemistry, but also in its morphology, i.e., to changes in its dynamical characteristics. This work studies the possibilities of the dynamical spectroscopy methods for evaluating changes in blood of cardiovascular ills.
Utilization of diffraction patterns in detection of hidden discontinuities in turbid media of biological significance
Authors: Papazoglou Theodore G. , Liu W. Q. , Manolopoulos Athanassios
Published: February 2023

Diffusely scattered light models have been extensively used by research groups on their effort to predict laser light's propagation through biologic tissue.1,2 This has provided useful results in the case of homogeneous isotropic materials. Biologic tissue is a highly complex medium consisting of single cells and various scattering and absorbing multicellular structures. The effect of light diffraction should not be ignored when the size and shape of hidden objects in the tissue is predicted via laser transmission measurements.