bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical Characteristics of Photon Paths and Optimization of the Tomography Algorithms for the Case of Strongly Scattering Media
Authors: Lyubimov V.V. , Murzin A.G. , Volkonsky V.B. , Utkin A.B.
Published: February 2023

We carry out calculations of the photon path statistical characteristics for homogeneous scattering medium with the model bodies (inhomogeneities) which are akin to that of biological objects of real tomography investigations. Convenient approximation formulas for definition of the mean photon paths are constructed for both the time and frequency domains and different inhomogeneity types (inhomogeneous absorption, scattering, and refraction as well as inhomogeneities of the combined type). The possibility to represent the signal perturbations due to the macroinhomogeneities as an integral along the mean photon path is used to solve the tomography reconstruction problem. This enables us to reduce this problem to the set of simultaneous equations for the discrete distribution of the macroinhomogeneity characteristics. The optimum discretization scale is chosen on the basis of area across which the macroinhomogeneity characteristics are averaged (this area is defined by the values of the diffusion and refraction coefficients of the medium).
Measurement of Saturation Intensities by Transient Nonlinear Refraction
Authors: Pilla V. , Impinnsi P.R. , Catunda T.
Published: February 2023

The nonlinear properties of ion doped solids have been studied by different techniques, particularly solids doped with Cr+3 and Nd+3 have been much investigated due to their applications as laser materials. In these materials the nonlinearity originates from the population of dopant ion metastable state, which has a complex susceptibility different from that of ground state. The real part of nonlinear refractive index is proportional to the polarizability difference Δα between excited and ground states and the imaginary part is proportional to the absorption cross section difference Δσ between excited and ground states(1). Most of these solids present nonlinearity which real part is one order of magnitude greater than the imaginary one. Z-scan is nowadays the most popular technique to measure n
2
and was recently applied to ion doped solids(2). In present work we used a time resolved Z-scan method to determine not only n2 but also the saturation intensity I, and the spontaneous lifetime τo (these values can be used to calculate the ground state absorption cross section σ1, Δα and Δσ). We should remark that although τo is usually easily measured by fluorescence, Is and σ1 are difficult to measured when you don’t know precisely the dopant ion concentration No or when it occupies different host sites.
Achromatic Liquid Crystal Phase Elements
Authors: Stalder M. , Schadt M.
Published: February 2023

Liquid crystal (LC) devices are described, which modulate the orientation of incoming linearly polarized light. The reorientation is due to the twisted nematic effect and is therefore achromatic. In contrast to practically all other LC devices, the elements described here use alignment layers with modulated orientations [1]. Two new classes of LC devices will be considered. First, LC devices with macroscopic modulations leading to polarization converter devices will be examined. They are capable of generating linearly polarized light with axial symmetry, the beam propagation axis representing the symmetry axis [2]. When such polarization converters are illuminated with circularly polarized light they behave as achromatic spiral phaseplates [3] of integer order.
Efficient cladding pumped Er3+/Yb3+-doped fibre amplifier and bending effect in cladding pumping scheme
Authors: Chen Z J. , Minelly J. D. , Dong L. , Vienne G. G. , Payne D. N.
Published: February 2023

Cladding pumping is now a well established technique for power scaling fibre lasers and amplifiers. For early work on cladding pumped Er3+/Yb3+ amplifier1, however, the efficiency was much lower than that of double clad Er3+ fibre amplifier. Here we demonstrate an efficient Er3+/Yb3+ co-doped double-clad fibre with efficiency over 40%. Bending effect in cladding pumping scheme is also discussed.
Collinear parametric generation in the visible with tilted fs pulses
Authors: Danielius R. , Piskarskas A. , Solcia C. , Foggi P. , Di Trapani P. , Andreoni A.
Published: February 2023

Group-velocity (GV) mismatch severely limits the efficiency of three-wave mixing processes with ullrashort pulses. Special conditions were found in the latest 80’s by Martinez, by Szabo' et al. and by Zhang et al. for obtaining GV matching in second-harmonic generation via achromatic or non-collinear phase-matching. More recently, we demonstrated that GV matching can be achieved in the more general case of tunable parametric generation by using suitable non-collinear phase-matching configurations [1,2]. Here we show that this can be obtained also in collinear parametric interactions, if the interacting pulses are made to propagate in the biréfringent nonlinear crystal with the pulse fronts suitably tilted respect to the phase fronts (Fig. 1). In fact, tilting the pump pulse by an angle γ modifies its collinear GV by the factor tan(ρ)tan(ργ), where ρ is the walkoff angle. Figure 2 shows the calculated γ values for which the GV of a 400 nm pump in type I BBO equals either the idler GV (dashed line) or the signal GV (dotted line); the full line gives the lilt angle γopt for which the signal- and idler-pulse GV's in the reference frame of the pump pulse are opposite, a condition that allows signal and idler to be amplified while staying locked to the pump, without broadening or gain saturation [3]. The relevant fact is that, since γopt is virtually constant over almost the entire tuning range, such a locked amplification can be obtained with a single set-up at any wavelengths.
High Efficiency, High Speed GaAs Thin Film Inversed MSM Photodetectors
Authors: Vendier Olivier , Jokerst Nan Marie , Leavitt Richard P.
Published: February 2023

MSM photodetectors are attractive for integration with receiver circuits since they have lower capacitance than p-i-n detectors with the same surface area. Low external quantum efficiency (20% to 40%), however, is a disadvantage of MSMs, which is primarily due to finger electrode shadowing. Several research teams had investigated novel ways to enhance the quantum efficiency such as transparent indium tin oxide electrodes (ITO-MSM) [1], and a Bragg mirror on the bottom to define a Fabry-Perot cavity [2]. The ITO MSMs demonstrated much higher quantum efficiency, but speed degradation was also noted due to the high resistivity ITO contacts. The Bragg mirror design produced only a moderate increase in efficiency. In this paper, inverted MSMs (I-MSMs), with metallized fingers on the bottom of the MSMs, are reported at 850 nm in GaAs/AIGaAs, with record external quantum efficiency for normal incidence MSMs at this speed.
Gain-Switched Solid-State-Laser Pumped by High Brightness Laser Diodes
Authors: Larat Christian , Feugnet Gilles , Schwarz Muriel , Pocholle Jean Paul
Published: February 2023

Solid state pulsed laser (such as Nd:YAG) with pulse width in the 10-100 ns range are well known Major technique, the Q-switching technique (switching of the internal cavity losses) delivers high peak powers. The long lifetime of the upper laser level (100-200 µs) leads to high level energy stored, but limits the pulse repetition frequency. Gain-switching (switching of the pump power) is the competing technique. The non insertion of a switching cell in the cavity leads to reduced losses, shorter and rugged lasers. But, as the gain-switching deals with the laser dynamic, the stored energy is lower than in Q-switching. Actually, achieving good efficiency in gain-switching mode needs high brightness pumping source. As the pump pulse duration (about 1 µs in our case) is small by comparison with Q-switching, gain-switching allows higher frequency (1-100 kHz) [1].
Poled Optic Al Fibres for Quasi-Phase-Matched Blue-Light Generation: Recent Developments
Authors: Kazansky P.G. , Pruneri V. , Russell P.St.J.
Published: February 2023

Recently, periodically patterned second order nonlinearities have been created in optical fibres by thermal poling in vacuo and cw quasi-phase-matched frequency conversion to the blue has been demonstrated [1]. The maximum blue light power detected was ~400 pW. corresponding to a fundamental power in the fibre of ~100 mW. Here we report recent developments in cw blue light generation in poled optical fibres. An increase of a factor ~10 in the conversion efficiency in comparison with the previous results has been obtained.
Aspects of a 1 kW, 1 kHz XeCl-laser with prospect to industrial applications.
Authors: Timmermans J.C. M. , Hofmann Th. , Couperus J. , van Goor F. A. , Witteman W.J.
Published: February 2023

Before excimer lasers can be implemented in large scale industrial production lines the performance of these lasers has to be proven. The 1kW, 1kHz-laser is being developed for such industrial applications. The X-ray pre-ionised laser operates in the resonant overshoot mode with a spiker sustainer circuit including a magnetic pulse compressor [1].
Nuclear Reactor Pumped Lasing Experiments on Fast Burst Reactor
Authors: Kononov V.N. , Bokhovko M.V. , Dyachenko P.P. , Korobkin V.V. , Prokhorov Yu. A. , Regushevskiv V.I. , Smolskiy V.N.
Published: February 2023

The concept of using nuclear energy to pump a laser by fission fragments of uranium can potentially be used to create large high power lasers that cannot be matched by other laser svstems[1]. That is possible owing to a high energy capacity of fission reactor and high penetration ability of neutrons in uranium multiplication systems. In the framework of designing of Energy Model of a Pulse Nuclear Reactor Pumped Laser System in IPPE[1] it was performed lasing experiments on 235U fission fragments pumping of 5d-6p atomic xenon 1.73 µm transition with 2 core fast burst reactor BARS-6 as a neutron source. The laser cell is a thin wall stainless steel tube 49 mm outer diameter and 400 mm lenth with internal 2.7 mg/cm2 235UO2 coating and filled Ar-Xe mixture (200: l) at 380 Torr. The laser cavity was formed by 6 m radius gold mirror and flat dielectric output coupler with reflectivity of 95% at 1.73 µm. The laser cell was surrounded by the 5 cm thick poliethylen moderator. In Fig. 1 thermal neutrons and laser output signal are shown. Thermal neutrons fluence was measured using Au radioactive indicator and was 1.7·1012 n/cm2. In Fig. 2 results of "master oscillator - two round trip amplifier" experiment are shown. As amplifier it was used a similar tube filled Ar-Xe mixture 2500 mm length with internal 5 µm thickness metal 235U coating and with optical windows. The energy gain in amplifier tube was ~ 4.
Complex-Coupled DFB Laser Structures with Absorptive Gratings (Invited)
Authors: Borchert B. , Siemens AG
Published: February 2023

Extensive theoretical and experimental work on complex-coupled (CC) DFB lasers, i.e. where the Bragg grating structure provides both real and imaginary coupling, have revealed this DFB-type as a promising alternative to the more common purely index-coupled (IC) DFB lasers. For the imaginary coupling both gain gratings [1,2] and absorptive gratings [3,4] have been realized. In both cases the reported laser characteristics are comparable to those of the IC-type. In the following results of state-of-the-art CC DFB lasers with absorptive gratings are presented.
Characteristics of a High Power, Compact, Annular, Waveguide CO2 laser.
Authors: Bethel J. W. , Colley A. D. , Baker H. J. , Hall D. R.
Published: February 2023

Large area, diffusion-cooled, RF excited, waveguide CO2 lasers with output powers in the multi-kilowatt regime were demonstrated several years ago [1] and are low cost devices which are relatively simple to construct. The annular format for diffusion-cooled CO2 lasers forms an alternative to planar slab geometries for producing ultra-compact lasers in the high power regime [2]. Some of the advantages of annular lasers over slab geometries include a reduction in the overall volume for the same electrode area, and the availability of low cost high tolerance metal tubing which can be used for the coaxial electrodes. However due to the high frequency of RF excitation required to produce high output powers from CO2 waveguide lasers, usually around 100 MHz, transmission line effects become important when scaling these lasers to large areas. In the case of planar slab CO2 lasers, this problem can be avoided by the technique of distributed parallel resonance to eliminate voltage variations along the length of the discharge. In annular lasers it is not usually possible to use this technique without blocking some of the annular aperture; hence length scaling of these lasers has previously been somewhat limited.
Anomalous spectral shape and diffraction of femtosecond time-and-space-domain holograms
Authors: Erni Daniel , Rebane Alexander , Ollikainen Olavi , Gallus Jiirgen , Wild Urs P.
Published: February 2023

Time-and-space-domain holography based on photon echoes in inhomogeneously broadened systems is a promising technique for ultrafast optical data storage and processing [1]. To faithfully reproduce the stored information it is important to control the spectral and spatial diffraction properties of the holographic gratings produced in the resonance medium.
The effect of laser frequency and phase fluctuations on coherent addition and erasure of photon echoes
Authors: Elman U. , Luo B. , Kroll S.
Published: February 2023

One important possible application of photon echoes is all-optical data storage. Photon echoes have a number of advantageous properties that make diem very good candidates for such applications, such as high areal density (1 Tb/cm2 has been projected [1], which should be compared with approximately 1 Mb/cm2 for commercially available CMOS memories today) and readout speeds >THz have been experimentally demonstrated [2]. We have addressed the problem of how to selectively erase data bits stored using photon echoes. One solution to this problem is to coherently add a new echo, phase shifted 180 degrees relative to the original echo, and thus achieve selective erasure of data [3].
Experimental generation of dark solitons using a novel Bragg grating based shaping technique
Authors: Leners R. , Foursa D. , Emplit Ph. , Haelterman M. , Kashyap R.
Published: February 2023

Dark solitons in optical fibres have received increased interest because of their potential advantages over bright solitons with respect to soliton interactions and sensitivity to noise in optical long distance transmission lines. Most recently, 10 Gbit/s pseudorandom dark soliton data have been generated and transmitted over 1200 km [1]. We demonstrate here a novel all-optical technique to generate a multigigahertz dark soliton train by using a high resolution filtering of a conventional mode-locked laser source [2]. The amplitude and phase filtering is performed by a specially designed fibre Bragg grating [3] and converts a 17 ps, 6.1 GHz bright pulse train into a 33 ps dark pulse train with an identical repetition rate. A numerical comparison between the temporal shape of the dark pulse train and its spectrum indicates that both the amplitude and the phase filtering are correctly performed i.e. that the dark pulses exhibit an approximate π phase shift across the dark part of the pulse.
Step-Ended Waveguide Soliton Demultiplexer
Authors: Garzia F. , Sibilia C. , Bertolotti M.
Published: February 2023

Optical solitons arise as self-trapped transverse spatial profiles in nonlinear planar waveguides or as temporal pulse shapes in fibers. Spatial and temporal solitons have been observed in different experiments, opening the way to realize, thanks to their interesting properties1, all-optical devices2,3. Soliton propagation through nonlinear interfaces, that is in condition of strong perturbation, has already been studied4,5. In this paper we want to study the propagation of a soliton beam in a waveguide with a gaussian refractive index profile, where the initial position of the maximum intensity of soliton is shifted with respect to the position of the maximum of the index profile. The index profile occurs along a direction orthogonal to both the propagation and the confinement direction. In this situation the beam is attracted torward the center of the index profile, acquiring a certain velocity that allows it to pass this point and to continue to move torward the other side of the index profile, decreasing its velocity. The situation is very similar to the trajectory of a mass in a gravitational potential hole.
Characterization of Optical Kerr Coefficient in Telecommunication Fibers by a Polarization Insensitive Method
Authors: Melloni A. , Amato L. , Boffi P. , Fellegara A. , Sacchetto P. , Martinelli M.
Published: February 2023

The availability of an accurate knowledge of the non-linear refractive index n2 is a really important issue in the study of optically amplified transmission systems. Recently the Kerr non linearity have been measured in optical Fiber by the observation of the pulse distortions due to Self-Phase Modulation (SPM) [1] and by a Cross-Phase Modulation (XPM) technique [2]. Both methods however suffer of a sensible optical beam polarization dependence.
New method to determine nonlinear transmission and gain coefficients of Kerr-lens mode-locked lasers
Authors: Zhavoronkov N.I. , Kalashnikov V.L. , PoIoyko I.G. , Mikhailov V.P.
Published: February 2023

In this letter we report the experimental method for optimization mode-locking efficiency of Kerr-lens solid state lasers. The transmission of intracavity aperture, formed by Kerr-lens effect and hard or soft slits, may be written as: T= To + σ I, To-transmission for low intensity radiation, 1-instantaneous intracavity intensity, σ - nonlinear transmission coefficient. The maximum value of σ corresponds to most favorable conditions for pulse regime generation and determines the efficiency of mode locking. Usually σ was estimated by calculations for nondisturbed by slit mode structure approximation [1]. We propose experimental determination of σ and use this value for simultaneous space and time analysis of mode-locking regime.
Stimulated Raman Amplification and De-multiplexing of Terawatt UV pulses: computer simulation
Authors: Savel’ev A.B. , Djidjoev M.S. , Mikheev P.M. , Platonenko V.T.
Published: February 2023

It is the key point for the interaction of powerful femtosecond pulses with solid targets to use pedestal free pulses with extremely short rise time. Besides, excimer amplifiers can deliver more energy if a few femtosecond pulses delayed by 1 nsec are amplified (so-called multiplexing). Commonly such pulses are summed directly on the target choosing the proper delay for each pulse. Consequently one can de-multiplexed simply the intensities of the pulses. For picosecond pulses it was proposed to de-multiplex using SRS process [1]. In this paper we show that Stimulated Raman Amplification (SRA) in the molecular gases of terawatt femtosecond light pulses could fulfil all the three goals mentioned above, i.e. it provides from a few 1 J pulses the single pedestal-free short-rise-time pulse with up to 70% efficiency. Moreover this pulse in most cases will be shorter as compared to the initial ones - its duration could be less than 100 fsec.
Parallel transfer of Optically Stored Information between Novel Bistable Optical Devices
Authors: Takei Hiroyuki , Shimizu Norio
Published: February 2023

We have fabricated a Fabry-Perot cavity containing a photochromic material called bacteriorhodopsin. It has two photochemical states with absorption peaks at 568 and 412 nm. Upon reversible photochemical change, the complex refractive index changes at the absorption edges of the two states, corresponding to 633 and 442 nm. With mirrors having high reflectivities at both wavelengths, the cavity can be set up in such a way that it would be in optical resonance at either one of the wavelengths depending on the photochemical state of bacteriorhodopsin.
Simulation of a self-switching nonlinear Bragg Reflector using realistic nonlinear parameters
Authors: Horst F. , Hoekstra H.J.W.M. , Driessen A. , Popma Th.J.A.
Published: February 2023

The self-switching effect in a nonlinear Bragg reflector is simulated using a Time Domain Beam Propagation Method. The device parameters were chosen to resemble a device based on SiON waveguide technology and nonlinear optical polymers.
Peculiarities of Chirped Short Pulse Scattering and Pulse Distortion
Authors: Kim Dalwoo , Xiao Gangyao
Published: February 2023

This paper is dedicated to study chirped pulse scattering by spherical water drops. Generalized Lorentz-Mie formulae1 are used to calculate the efficiencies of extinction and backscattering when a chirped pulse is scattered by spherical particles. Gaussian pulses of different linear chirps(b) with a constant pulse filling coefficient(l0=1.98) have been studied. The calculation illustrated that chirped pulse scattering shows much different peculiarities from carrier wave scattering(Fig.1). The slowly-varying background of the extinction and backscattering curves is damped by the chirp, and when the pulse is deeply chirped, the maxima and minima of the background curves reduce to disappear and the efficiency curves illustrate a step-like dependence on the sphere size. Using the Fourier theorem, we also studied the temporal dependence of the scattered intensity and the pulse distortion(Fig.2). The pulse chirp affects the scattered pattern definitely for moderate and large particle size. Multi-secondary pulses are generated because of the pulse chirp and even sub-secondary pulses will occur if the incident pulse is deeply chirped. The pulsewidths of the scattered secondary and sub-secondary pulses are shorter than that of the incident pulse. The scattered intensity and pulse wave form are dependent on the sign of the pulse chirp but the efficiencies of extinction and backscattering seems blindness which depend only on the amount of the chirp regardless of up-chirp or down-chirp.
Five-membered Heteroaromatic Hydrazone Derivatives for Second-Order Nonlinear Optics
Authors: Meier U. , Wong M. S. , Pan F. , Bosshard Ch. , Günter P. , Gramlich V.
Published: February 2023

In the past decades, there have been extensive research efforts in developing new highly efficient organic materials with large second order susceptibilities because of their potential applications in optical signal processing and frequency conversion. Molecules possessing a large firstorder molecular hyperpolarizability ß are an essential prerequisite for achieving large macroscopic susceptibilities χ(2). The molecular nonlinearity of the classical, nonlinear optically active molecule, which usually contains an electron donor and an electron acceptor connected by a π-conjugated core, can be enhanced by increasing the electron donor or electron acceptor strength, elongating the length of the conjugated core, and reducing the ground state aromatic character.
High pulse rate diode laser side-pumped 1.54 μm Yb:Er:glass laser
Authors: Hovland Harald , Stenersen Knut
Published: February 2023

Diode lasers are attractive pump sources for 3-level rare earth doped lasers, because they provide high pump intensities with a minimum of heating of the laser material(1). Glass lasers are particularly interesting with respect to diode pumping, since the relatively broad pump band in glasses relaxes the need for accurate pump wavelength tuning. In this paper we study diode side pumping of Yb:Er:glass(2) and report on efficient operation up to 10 Hz pulse rate. We observe a significant reduction in the output energy in Q-switched operation relative to free-running operation, and we study the mechanisms causing this reduction.
Operation And Degradation Characteristics Of High Power Broad Area AlGaAs and InGaAsP Based Lasers
Authors: Syrbu A. V. , Yakovlev V. P. , Suruceanu G. I. , Mereutza A. Z. , Katughin O. V. , Predescu M.
Published: February 2023

We have used AlGaAs/InGaAs and InGaAs/InGaAsP strained quantum well broad area lasers grown by metal organic chemical vapor deposition to study their high power and degradation characteristics. Laser facets are passivated with zinc selenide and low reflectivity (LR=5%) and high reflectivity (HR=95%) SiO2/Si coated using vacuum deposition1. These lasers emit in the vicinity of 1000 nm with external quantum efficiency of 70 to 85%. Series resistance of 0.1 to 0.3 Ohm and thermal resistance of 3 to 5 K/ W for lasers with 0.1 mm stripe width and 0.8 to 1.5 mm cavity length are typical for these lasers when mounted on copper heat sinks using lead-tin solder.
Gas Imaging Using Infrared Gas-Correlation Spectroscopy
Authors: Sandsten Jonas , Andersson Mats , Edner Hans , Svanberg Sune , Blomberg Thomas
Published: February 2023

In many applications there is an interest to find and visualise gas plumes in real-time. Images of gas concentration distributions are needed in several environmental studies. Global monitoring of greenhouse gases from spacecraft based systems arc important. An industrial application is hydrocarbon emission monitoring from petrochemical installations and leakage detection along pipelines. Indoor monitoring of working environment and surveillance of hazardous gases are other fields where imaging is useful.
An innovative multiparametric Lidar system developed under “Progetto Sud” of Istituto Nazionale per la Fisica della Materia
Authors: Ambrico P. , Amodeo A. , Armenante M. , Berardi V. , Boselli A. , Bruzzese R. , Capobianco R. , Di Girolamo P. , Pappalardo G. , Spinelli N. , Velotta R.
Published: February 2023

We have developed a multiparametric Lidar system by which is possible to carry out simultaneous measurements of: i) atmospheric aerosols, ii) water vapour profiles, iii) temperature and density profiles, iv) atmospheric transmissivity, and v) main atmospheric pollutants. The system is realised by a Nd:YAG laser pumping a dye laser capable equipped with a dual wavelength device. By this way the dye laser emission is made of two alternate (shot by shot) close wavelengths, allowing DIAL measurements of specific pollutants.
Diffraction Excitation of TEM00 Mode of Solid State Ring Laser
Authors: Golovin A. B. , Khiznyak A. I. , Kreminskaya L.V.
Published: February 2023

The high sensitivity of the ring laser to the intensity of injected radiation makes possible to investigate experimentally excitation of TEM00 mode of the ring laser We have investigated the intensity ratio of counterpropagating waves in the ring cavity neodymium doped phosphate glass laser with passive optical isolator (POI) during the first pike (Fig 1).
Astigmatism-compensated folded cavity with minimal sensitivity to lengths variations
Authors: Foing Jean-Paul
Published: February 2023

Linear folded cavities are widely used as they meet the requirements of a small spot size in the short arm needed for high gain, and a collimated beam in the long arm, allowing the insertion of different optical elements for wavelength selection or Q-switching. The spherical mirror used with an oblique angle of incidence introduces astigmatism, but as explained in the well-known paper of Kogelnik and al. [1], these distortions can be balanced by the astigmatism of a Brewster angle element Such a cavity should be designed not only for astigmatism compensation but also for minimal sensitivity to lengths fluctuations [2], that could generate output power variations.
Large Bandwidth High-Efficiency Freouency Conversion into a Spin Multiplet
Authors: Popescu F.F. , Marica F.
Published: February 2023

For triple resonances into a spin multiplet of a dilute paramagnetic solid, when the spectroscopic bridge (SB) conditions are fulfilled, high-efficiency microwave frequency conversions [1], or phase sensitive amplifications [2] have recently been predicted. Unlike the optical case. [3]. the efficiency of these processes is expected to reach the maximum value, when the coherent mixing of the three quasimonochromatie fields (the parametric process) is negligible [4].
Efficient frequency tripling in bulk germanosilicate and Er3+ - doped germanosilicate glasses pumped at 1.319 µm
Authors: de Araujo M. T. , Vermelho M. V. D. , Hickmann J. Miguel , Gouveia-Neto A. S.
Published: February 2023

In this work we report on the generation of third-harmonic 120 µW average power light at 440 nm in bulk GeO2-SiO2 and Er3+-doped GeO2-SiO2 glasses pumped by a Nd:YAG at 1.319 pm. In the experiment, a Nd:YAG laser operated at 1.319 µm was employed as the pump source. The laser delivered 150 ps pulses at 100 MHz repetition rate in a 700 ns Q-switch envelope at 1 kHz frequency. Our investigations were performed utilizing optical fiber preform samples. The preforms had both germanosilicate core and Er3+-doped germanosilicate core. Figure 1 shows a typical power spectrum of the third-harmonic signal at 440 nm generated in a 2 mm thick sample of 8% GeO2 - doped silica optical fiber preform, for an average pump power of 400 mW. The light at 440 nm was the unique visible signal observed in the spectral region of 400 - 700 nm and was generated instantaneously with pump light illumination. The signal was generated in bursts of Gaussian shaped Q-switch envelopes of ~ 400 ns duration and the individual modelocked picosecond pulses in the envelope could also be observed. The pump power dependence of the output visible signal was investigated and presented a cubic power law dependence with pump intensity as expected for a parametric third-harmonic generation process. For the highest average pump power available, as much as 120 µW average power of blue-violet light at 440 nm was generated, corresponding to peak pulse powers of ~ 0.2 W. We have also tested, Er3+- doped germanosilicate fiber performs samples and the third-harmonic power spectrum has essentially shown the same characteristics as the undoped samples. However, in contrast to undoped samples, the signal intensity dependence with pump power for Er3+-doped glasses, has shown an initial cubic dependence for low powers and fourth order for intermediate powers, as illustrated in graph of Fig.2. For high pump powers an exponential growth was observed. This behavior is attributed to two and three-photon ressonance enhancement of χ(3) [1, 2].
Dynamics in a CO2 Laser with Combined Action of Pump Switching and Loss Modulation
Authors: Pisarchik A. N. , ólafsson A.
Published: February 2023

A CO2 laser with modulated parameters displaying a variety of complex behavior has been the subject of much research over the last decade [1,2]. All previous works meant deal with the lasers operating in a cw regime. The dynamics of a pulsed laser is a more complex subject and its investigation requires sophisticated theoretical models and experiments. In this report we show some features of the dynamical behavior of a CO2 laser with pump switching and sinusoidal loss modulation.
Self-homodyne Laser Linewidth Measurements
Authors: Ludvigsen Hanne , Kokkonen Jukka , Tossavainen Mika , Kaivola Matti
Published: February 2023

Accurate knowledge of the laser linewidth is essential for many applications in coherent optical communication, optical metrology and high-resolution spectroscopy. The self-heterodyne/homo-dyne measurement technique is an established method for measuring the linewidth of semiconductor lasers [1, 2]. The basic idea of the technique is to convert the optical phase or frequency fluctuations of the laser into variations of light intensity in a fiber-optic interferometer. In the interferometer, the optical signal is compared with a delayed replica of itself and detected with a fast photodiode. In the heterodyne case, an acousto-optic modulator is used to shift the spectrum in order to reject the delected DC signal in the photodiode and to allow use of a standard RF spectrum analyzer to measure the spectrum. The optical losses in the acousto-optic modulator arc, however, substantial and reduce the overall sensitivity of the setup, typically by several dB.
High-Accuracy Measurements of the Spacing of Diffraction Gratings in the Range 0.28 μm - 0.50 μm Using Laser Interferometric Diffractometry
Authors: Korotkov V. I. , Pulkinl S. A. , Vitushkin A. L. , Vitushkin L. F.
Published: February 2023

At the BIPM and the VNIIM laser interferomctric diffractometers (LID) [1,2] have been constructed for high-accuracy measurements of the spacings of diffraction gratings. The least measurable spacing is λ/2 where λ is wavelength of laser radiation in use. Periodic short-length line scales incorporating diffraction gratings have been developed. These can be used for the calibration of high precision length measuring systems in micrometre and nanometre ranges.
Velocity Measurement of Diffuse Object by Using Modulated Dynamic Speckle
Authors: Popov Ivan A. , Veselov Leonid M.
Published: February 2023

Up to now, several methods for velocity measurement using speckle dynamics have been proposed. They are based on the varlation of the correlation function or the power spectrum of speckle intensity. These methods are simple and rapid to apply to measure tangential component of body's velocity but accuracy of velocity measurement is rather low. The use of amplitude or phase grating to modulate the speckle pattern was suggested also for measurement of diffuse object velocity[1,2].
A Laser Polarimetric Sensor for Measuring Angular Displacements of Objects
Authors: Klimkov Yu. M. , Shribak M.I. , Shkadarevich A.P.
Published: February 2023

One of the promising applications of laser autocollimating polarimetric sensors is measuring angular displacements of objects. For this purpose a parallel-sided plate, cut out of a birefringent crystal, and a retroreflector are mounted onto the object. The collimating beam of the polarimeter is sighted at the object and reflected back by the retroreflector. By this the beam pass two times through the birefringent plate. Retardance, caused by the plate in the beam, is proportionate to plate's tilt. Having measured the returdance by means of the polarimeter one can define the angle of the object's tilt [1].
Liquid Crystalline Fiber Optic Pressure Sensor Based on Twisted Nematics Cells
Authors: Woliński Tomasz R. , Domański Andrzej W. , Konopka Witold , Karpierz Mirosław
Published: February 2023

The use of liquid crystal (LC) materials in applications to fiber optic sensing of hydrostatic pressure in both lower (of the order 1 MPa) and higher (up to 100 MPa) pressure regions was recently reported1-3. Some of the LC materials as chiral nematics possess strong rotatory power manifesting itself in rotation of linear polarization of the light coming through a LC cell. This phenomenon has become a basis of a new method of pressure sensing4,5 and resides in detecting changes in helicoidal pitch (characterizing the chiral nematics structure) under pressure.
Profiling of carrier density in semiconductor lasers via spectral analysis of side spontaneous emission
Authors: Sargent Edward H. , Pavlidis Dorothy , Golinescu Nicolae , Xu J.M. , Clayton Richard , Anis Hanan , Kim H. B.
Published: February 2023

Previous measurements of spontaneous emission from a semiconductor laser have either ignored longitudinal effects while focussing on spectral phenomena1, or have sacrificed spectral information in favour of resolving longitudinal variations2. We have, for the first lime, obtained a longitudinal carrier density profile by analyzing spontaneous emission spectra measured from the side of a laser cleaved along its length 20 μm from the ridge. Designed for reduced sensitivity to temperature fluctuations and alignment imperfections, our technique is applicable to the studs of internal operating mechanisms, including such el feels as spatial hole burning and optical damage, in both Fabry-Perot and DFB lasers.
Pulsed, laser re-crystallization of high-speed steel surfase in ultrasonic field
Authors: Gureyev D.M.
Published: February 2023

The peculiarities of process of the pulsed laser re-crystallization of T1 high-speed steel surfase in the ultrasonic field were studyed in this work. The changes of structural-and-strained condition of the surfase layers within the laser-ultrasonic influence and the following bulk tempering of crystallized melt were analysed. The YAG:Nd - solid-state laser with the pulse duration of ~ 1 ms and the energy per pulse up to. 300 J was used as the laser source. The ultrasonic vibrations with the frequency of 22 kHz and the amplitude up-to 10 μm were coupled into the laser melt continuously along or across the direction of laser influence. The one-hour bulk tempering of crystallized melt was realized in the temperature interval of 450-650 °C. In addition to the results [1], which show the influence of ultrasound coupling-in scheme on the change of proceeding speed of the heat-and-mass-transfer processes in the bath of laser melt, it was shown the distinctive peculiarity of longitudinal scheme of the ultrasound coupling-in during the rapid crystallization of laser melt in the formation of texture with the isolated [100] crystallographic direction. The following bulk tempering leads to the some more greater development of given texture with the maximum within 600 °C. It was noted the increase of tension residual stresses within the rapid crystallization of laser melt in the ultrasonic field, that apparently is the oonsequenoe of ultrasound influence on the process development of peritectic transformation of the δ-ferrite in the austenite. The decay of oversaturated solid solution by the following bulk tempering leads to the formation in the surfase layers of pressing residual stresses, which reach the greatest value in case, when the pulsed laser re-crystallization proceeds within the simultaneous coupling-in of ultrasonic vibrations into the melt in the longitudinal scheme. Side by side with the earlier obtained results [2] within the bulk tempering of oversaturated solid solutions the obviously expressed effect of increase of the lattice parameter of isolated basic M6C carbide phase up to 1.122 nm was fixed, that indicates on the considerable increase of tungsten portion in the composition of this carbide. For this the influence of ultrasonic vibrations is not affected on the observed conformity with a law.
Ellipsometric Investigation of Micropore Formation in Silicon Layers Implanted by High Dose Ions of Krypton
Authors: Buynova E.Y. , Galjautdinov M.F. , Kurbatova N.V. , Shtyrkov E.I.
Published: February 2023

New modification of por-Si have been discovered [1] to be formed as a 30 nm microporous layer (30 nm) as a result of laser annealing of c-Si implanted by krypton (:wave length of 694,3 nm, pulse width of 50 ns, energy density of 0.3 J/cm2).In the present work,in order to study influence of high dose implantation and laser annealing regimes on pecularities of formiation of such microporous layers, the p-silicon samples with (111) orientation were examined at higher doses of krypton ions (6*1015-2.4*1017 ion/cm2) and laser energy density (0-2.3 J/cm2).The ellipsometric measurements were performed with LEF-3M1 ellipsometer at a probe wave length 632.8 nm,room temperature and normal pressure.The angle of probe beam incidence was 70 degrees. Measuring the ellipsometric parameters followed by calculating of the optical constants n and k in the case of step by step anodic etching we have studied depthward transformation of the disordered undersurface layers depending on laser energy density.The profiles of complex refractive coefficient are shown in Fig.1. Behaviour of the n-profiles (Fig.1a,curves 2-4) has no agreement with ordinary data because, nearly to the surface, n is as little as monocrystalline silicon’s one (curve 5). Such a transformation of structure of nearsurface layer is due to formation of dense grid of micropores that results in considerable increase of k-coefficient as well (Fig.1b).Recrystallization of the disordered layer due to laser annealing takes place while increasing laser energy density., In dependence on regimes of irradiation the transformation process of nearsurface layer structure has some interesting features,for instance, diffusion of cryplon and moving of micropores to the surface at lower energy density.
Wavelength dependent second harmonic generation from surface bound Na clusters: Comparison between experiment and theory
Authors: Balzer F. , Rubahn H.-G.
Published: February 2023

The excitation of a collective vibration of the electron gas inside a large metallic cluster ("surface plasmon excitation”) by means of. e.g., laser irradiation gives rise to a large enhancement of the electromagnetic field at the cluster surface [1]. This increase in field strength is believed to be one of the main causes for the surface-enhancement of nonlinear processes such as Raman scattering (SERS) [2], second harmonic generation [3] or degenerate four wave mixing [4].
Optimisation of a Raman Frequency Converter based on highly Ge-doped fibres
Authors: Peschel U. , Shipulin A. , Onishukov G. , Lederer F.
Published: February 2023

Many conventional long-haul transmission lines are operated at λ= 1.32µm. The problem of all-optical amplification is not solved yet for this wavelength range. In line Raman amplification seems to be promising. Unfortunately their is also no efficient light source for the Raman pump wave at λ= 1.24µm. It was proposed to generate this light by a NdYag-laser operating at λ= 1.06µm and to convert it down via a three stage rain an process. Recently some progress could be achieved by the introduction of Ge-doped fibres with low excess losses but with enhanced Raman gain. The aim of this paper is to model and to optimise a fibre resonator for this scheme (see Fig.l). The whole resonator is described by the following set of differential equations.
Laser Spectrometer Based on Optical Parametric Oscillator for Trace Gas Detection in Multicomponent Mixtures
Authors: Bohren A. , Sigrist M.W.
Published: February 2023

The selective and sensitive detection of trace gases in multicomponent gas mixtures by means of absorption spectroscopy requires narrowband continuously tunable laser sources. Newly available optical parametric oscillators (OPO) meet these requirements almost perfectly. Our commercial nanosecond OPO - system is pumped by the third harmonic of a Nd:YAG laser and offers a tuning range from 440 to 1800 nm. The linewidth of less than 0.2 cm–1 at energy levels of several mJ per pulse is maintained over the whole tuning range. At standard pressure the absorption linewidths of most environmental relevant trace gases such as CO2, CH4 and volatile organic compounds (VOC's) match with the laser linewidth thus making the system particularly useful for the analysis of ambient air samples. First experiments with a specially designed nonresonant photoacoustic cell on CO2 and CH4 overtones in the idler range of the OPO (710 - 1800 nm) demonstrate the power of this approach. An example is shown in Fig. 1 for CO2.
Self-Adaptive Solid-State Lasers Using Dynamic Holographic Mirror
Authors: Damzen M.J.
Published: February 2023

Recent work is presented on 3-D saturable gain-gratings, optically-written by spatial hole-burning in the active lasing medium, as efficient self-adaptive diffractive optical elements [1] for application in gain media phase conjugators [2] and for adaptive spatial, spectral and Q-switching control of high-gain solid-state lasers [3,4,5,6], Description will be made of gain-gratings written by spatial hole-burning when coherent beams, at the lasing wavelength, interfere in a gain medium. Such 3-D gain gratings, which have a persistence for the upper-state lifetime of the gain medium, can be considered as volume gain holograms and the application of these adaptive grating devices can be considered as a type of dynamic "gain holography".
A Tunable Narrowband Holographic Ti:Sapphire Laser
Authors: Minassian A. , Crofts G. J. , Damzen M. J.
Published: February 2023

Experimental and theoretical studies have shown that gain gratings in inverted media can exhibit greater-than-unity diffraction efficiency due the stored energy and in four-wave mixing (FWM) can produce very high phase conjugate reflectivities. Such experiments have been performed with laser-pumped Ti:sapphire resulting in reflectivities of nearly 400% at 780nm [1]. It has also been demonstrated that spontaneous gain grating formation can lead to a novel type of laser resonator [2], where the resonator is formed between a conventional mirror and a 'holographic' mirror. The holographic mirror contains the phase information of distortions in the loop and can adapt to cancel out aberrations, as well as provide spectral narrowing.
High resolution observations of polar stratospheric clouds by the alomar doppler wind and temperature system
Authors: Rees D. , Vyssogorets M. , Nilsen P-E , Gandham I. , Rees David
Published: February 2023

The Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) at Andoya, Norway (69°N, 16°E, von Zahn and Rees, 1994), is a complex multi-instrument facility using lidars, radars and passive IR and Visible-wavelength instruments to study the complex behaviour of the Arctic Stratosphere and Mesosphere (von Cossart et al, 1995, 1996).
Mode Competition in a Fabry Pérot Semiconductor laser: Travelling Wave Model with asymmetric dynamical gain
Authors: Homar M. , Balle S. , Miguel. M. San
Published: February 2023

Fabry-Perot semiconductor lasers usually exhibit a multi-longitudinal mode behavior which is revealed in their power spectra. The relative power of the longitudinal modes varies with pump current, while the competition among them is influenced by several physical mechanisms such as spontaneous emission noise, spatial hole burning (SHB), spectral hole burning, and carrier diffusion. This competition gives rise to a variety of dynamical phenomena which most notably include mode-beating and mode-hopping.
Mode behaviour of a waveguide annular CO2 laser with a Talbot cavity
Authors: Lapucci A. , Ciofini M. , Mascalchi S.
Published: February 2023

The annular geometry represents an interesting alternative to the slab format for diffusion cooled RF excited CO2 lasers. Typical draw backs of this scheme are related to the difficulties encountered in extracting a good quality beam [1] and in uniformly distributing the power in the discharge. Some effective solutions to the latter problem have recently been found [2,3], We have focused our attention to the former problem, experimentally testing the use of a Talbot cavity together with a phase-correcting mirror on the 100 W class annular laser described in Ref.[1]. The extraction efficiency obtained so far with this scheme is half that of a simple plane-plane guided resonator producing a multimode beam. The beam quality on the other hand appears sensibly enhanced.