bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarisation of a Neodymium Laser with a Passive Q-Switch Based on a Cr4+:YAG Crystal
Authors: Il'ichev N.N. , Kir'yanov A.V. , Gulyamova E.S. , Pashinin P.P.
Published: February 2023

Previously we reported [1] the experimental observation of the drastic dependence of the state of polarisation of a neodymium laser passively Q-switched with a Cr4+:YAG crystal upon relative orientations of the switch and an intracavity polariser The aim of the present paper is to report, for the first time to our knowledge, a theoretical study of this phenomenon.
Analysis of Coupling Coefficient in DFB and DBR Circular Grating Waveguide Lasers
Authors: Kossek Tomasz , Witonski Piotr , Szczepański Pawel
Published: February 2023

High-power planar waveguide lasers that emit in a single mode are of interest for applications in such diverse fields as satellite communications, nonlinear optics or optical computing, for example, an output power of an emitting semiconductor laser may be increased by broadening the stripe width of the active region. However, this generally causes multimode operation in the laser. Furthermore surface emitting lasers provide a broad emission regin to generate large amounts of optical power, but large surface area emitters also produce multimode emission.
Killing Bacillus cereus bacterial endospores with Nd:YAG laser light and UV irradiation
Authors: Armstrong Graham N , Watson Ian A , Ward Glenn D , Wardlaw Alastair C , Yeo C B Allen , Stewart-Tull. Duncan E
Published: February 2023

The resistance of bacterial endospores to both heat1 and UV irradiation is well known. Laser light has been shown previously to have a killing effect on spores in relation to medical instruments2. In the present case, Nd:YAG laser light and UV irradiation was combined into a treatment process and the subsequent killing effect statistically analysed. After exposing spores, lawned on nutrient agar plates, to UV irradiation, from a 2 × 8W source (distance 24cm, output 190 μWcm2), inactivation caused by laser light was increased. Exposure to the laser light alone (energy density 3000 Jcm−2) gave a 10% zone of inhibition, but with a previous exposure to UV for 4 min, the zone of inhibition increased to 55-65%. This is shown in Figure 1. The bacterial lawns were showing significant signs of inhibition after 6 min of UV exposure. To investigate further effects of laser and UV treatment, spore suspensions on stainless steel discs were pre-treated with laser and exposed to UV irradiation, with a varying delay between the two treatments. The experiment was a multifactorial design. Figure 2 shows that as the individual factors, laser and UV exposure, were increased, a reduction in remaining cell viability was observed. There was increased killing when a longer delay (15 min as opposed to 10 min) was employed. The results were analysed with the linear general model. It was found that as single factors, all three agents were significant. The laser was more significant than the UV at the exposures given. It was also found that a high laser pre-treatment and high delay had a significant interaction, (95% confidence limits). This could suggest that after a high enough laser treatment the spores were beginning to lose some of their resistant properties. The results did not suggest that there was a significant interaction between either the laser and UV, or the laser. UV and delay.
Excited-State Absorption of Er3+-Doped LinbO3
Authors: Burlot-Loison R. , Doualan J.-L. , Le Boulanger P. , Han T.P.J. , Henderson B. , Moncorgé R. , Boulon G.
Published: February 2023

Excited state absorption (ESA) has been investigated in Er3+ -doped LiNbO3 after pumping in the 4I13/2 level. Because of its long lifetime (3 ms), the 4I13/2 Er3+ ion level can show an important absorption towards higher energy levels. Especially. 4I13/2 → 4I9/2 ESA takes place not so far from the eye-safe 4I13/2 → 4I15/2 emission (maximum at 1530 nm) and can then reduce the laser performances.
An influence of thermal lensing on the laser operaton in Chromium-doped forsterite at room temperature
Authors: Zhavoronkov N. , Mikhailov V.
Published: February 2023

The pump power absorbed in the solid-state laser crystals gives rise to thermal loading effect owing to the temperature dependence of the refractive index n
l
. Because of this the characteristics of the laser can be drastically changed, so this effect is important to design efficient laser system. The temterature distribution T(r,z) inside the laser od in the steady state satisfies a well-know differential equation and the resulting thermal variation of n
l
can be analytically evaluated in terms of the exponential integrals [1]:
Analysis of thermal effects in flared semiconductor laser amplifiers
Authors: Bonnefont S. , Mariojouls S. , Gilard O. , Vergnenegre C. , Lozes-Dupuy F.
Published: February 2023

Considerable progress in high-power diffraction-limited sources has been made owing to the use of flared semiconductor laser amplifiers. The broadening of the gain electrode along the length of the amplifier allows the wave spreading while maintaining its amplification level, and reduces the beam filamentation phenomenon. Diffraction-limited powers as high as 1 W CW have been demonstrated from such devices, however thermal effects can strongly influence their performance.
Long pulse lasing of Nd-lasers while using FTIR Q-switches
Authors: Bufetova G.A. , Nikolaev D.A. , Lakhno P.R. , Shcherbakov I.A. , Tsvetkov V.B.
Published: February 2023

The lasing efficiency in the Q-switch mode depends most of all on the losses, incoming with all the optical elements and the density of the intracavity radiation. It was shown [1], that the maximal efficiency of the operation of Nd-lasers could be achieved while using Q-switches with frustrated total internal reflection (FTIR Q-switches) which possess extremely low losses and high optical durability.
II-VI Infrared Resonant Cavity Emitters with 2 Postgrowth Evaporated Dielectric Mirrors
Authors: Roux C. , Filloux P. , Mula G. , Pautrat J.-L.
Published: February 2023

The use of microcavity-enhanced light emitters in the infrared gains interest in the applied research domain because of the improved efficiency and directionality that can be achieved with respect to the usual heated-filament sources.
High frequency current modulation of high order transverse modes in vertical-cavity surface emitting lasers
Authors: Valle A.
Published: February 2023

Weakly index guided vertical cavity surface emitting lasers (VCSELs) are analyzed in the multi-transverse mode regime. An efficient dynamical model is developed that takes into account all the transverse modes (LP
mn
) supported by the waveguide. Mode partition noise in a current modulated VCSEL is studied taking into account the azimuthal degree of freedom. Different transverse modes can be excited with a probability that is numerically calculated. For high injection currents modes that are not favoured in the steady state can be the ones excited with higher probability. The excitation probability is similar for azimuthally orthogonal modes. This symmetry can be broken by selecting a particular high order transverse mode by using azimuthal dependent current profiling: injection is performed where the mode has appreciable power. This selection can be achieved over current ranges larger than ten times the threshold current. The radial range of injection current to obtain this selection is shown to be wide.
InAlSb/InSb Quantum well mid-infrared Diode Lasers.
Authors: Ashley T , Carroll M , Elliott C T , Jefferies R , Johnson A D , Murdin B , Pryce G J
Published: February 2023

The InSb team at DERA Malvern have been developing mid-infrared emitters based on InAlSb and InSb, for potential use in the areas of remote detection of pollutant and toxic gases, general spectroscopy, eye-safe range finding and secure communications. Room temperature operating LED’s have been demonstrated previously, as well as InSb lasers up to 100K and InAlSb lasers to 155K with an output power of 28mW at 80K.
Nonlinear compression of tilted light pulses
Authors: Danielius R. , Dubietis A. , Valiulis G. , Tamošauskas G. , Piskarskas A.
Published: February 2023

Nonlinear pulse compression under special conditions of large group-velocity mismatch (GVM) and strong energy exchange suggested for the first time 8 years ago [1,2], was demonstrated to be a simple and efficient method to generate powerful femtosecond pulses via frequency doubling of picosecond Nd-laser pulses in KDP crystal. However, the direct transfer of this technique to other wavelengths or other well-developed laser sources (Ti:sapphire, for instance) encounters serious problems related to the lack of nonlinear crystals with suitable dispersive properties. To this regard, the use of tilted pulses offers unique possibility to adjust the GVM in a nonlinear crystal for a particular wavelength [3,4].
A compact fiber laser with butt coupled semiconductor saturable absorber mirror (SESAM)- a further step toward an all solid state short pulse laser
Authors: Glas P. , Naumann M. , Schirrmacher A. , Pertsch Th. , Däweritz L. , Hey R.
Published: February 2023

We have passively Q- switched and mode locked a Neodymium doped fiber laser with a semiconductor saturable absorber minor (SESAM). The fiber used has an annular shaped active region (M-profile fiber) Fig.1a, possessing the advantage that the pump light may be completely absorbed over a short length. Butt coupling a SESAM at one of the fiber ends is therefore possible because there is no pump light left leading to an unwanted saturation of the absorber. We have made a modal analysis in the scalar approximation comparing the absorption of the M-profile fiber and a standard double clad one provided high power diode lasers are used for optical pumping. Figs.1b give examples of LPm p modes of a M-profile fiber. In the calculations the following parameters were used: pump wavelength λ= 8o3 nm, Δcorc-first cladding = 0.003 and Δfirst-second cladding = 0.04; 1)M-profile fiber: 5 µm ring width and 85 µm ring centre diameter; 2) double clad fiber: 100 µm pump core diameter, 6.5 µm doped core diameter. For the M-profile fiber not only the low order modes i.e. LP01 interact strongly with the doped region but higher order modes do as well. For the double-clad fiber it is only the field of the very low order modes (here LP0 1,) have an overlap with the active material whereas all higher order modes have almost nothing. Based upon the theoretical findings we have realised a set-up where the SESAM is directly attached to the fiber just as the incoupling mirror. Such an optical scheme has not been realised up till now as we believe. The SESAM was polished at the back side possessing a reflectivity of about 98%. The fiber length was 200 cm, the amount of pump radiation leaving the fiber was less than 5%. The measured pulse width using a fast detection electronics ( risetime 60 ps ) is shown in Fig. 1c. For a certain range of pump powers we have obtained Q-switch pulses with a very low jitter (< 1% ). Locking a large bandwidth could not be achieved being partially due to the SESAM and to the multimode behaviour ( azimuthal direction ) of laser.
Femtosecond dynamic holography in C60 solutions
Authors: Bespalov V. G. , Krylov V. N. , Staselko D. I. , Rebane A.
Published: February 2023

Fullerene molecules (C60, C70, C76) are known to posses unusual nonlinear optical response characteristics, which make them attractive for variety of applications, including optical limiters, recording media and switching devices [1-3]. These nonlinear properties are associated with the fullerene molecules having unique carbon-carbon single-and double bonds and combination of singlet- and triplet excited electronic states. Due to broad spectral range of the nonlinear response, fullerene-based materials may be used for recording of dynamic holograms from UV to near IR. In this paper we present results of experiments, where we study efficient self-diffraction from dynamic gratings recorded in C60 solution in orto-xylene using excitation with energetic 150-fs-duration pulses at 780 nm wavelength.
Nonlinear Pulse Switching and Compression in a Dispersion-Imbalanced Loop Mirror
Authors: Khrushchev I. Y. , White I. H. , Penty R. V.
Published: February 2023

Gain-switched and Q-switched laser diodes have long been of interest because they can be directly modulated over widely tuneable repetition rates. However, the pulses generated in such diodes are typically longer than a few picoseconds duration and hence compression techniques have become of great interest.
150 fs Cross-Gain Modulation Experiments on Semiconductor Optical Amplifiers
Authors: Hessler T. , Pleumeekers J. L. , Selbmann P. E. , Dupertuis M.-A. , Deveaud B.
Published: February 2023

Ultrafast gain dynamics in semiconductor optical amplifiers (SOA’s) is of great interest because of the potential application of SOA’s in high-speed optical networks. It also enables to get a better understanding of the fundamental physical processes involved in the interaction between a short optical pulse and a high density plasma. So far, the ultrafast gain dynamics in SOA’s has been mainly studied by means of standard pump and probe (P&P) measurements in which the wavelengths of the pump and probe are identical. Here, we present a new experimental technique which is an ultrafast cross-gain modulation (XGM) between a 150 fs pump pulse and a weak cw probe signal. The advantages of the XGM over the P&P technique are two-fold. Firstly, the probe wavelength can be varied and therefore the gain recovery at different wavelengths around the pump wavelength can be obtained. Secondly, the probe signal is a cw signal, thus having a very narrow linewidth and hence a high spectral resolution. Consequently, information is obtained on the spectral carrier population distribution and its recovery.
Nonresonant Electrooptic Light Phase Modulation in Bulk Semiconductors
Authors: Jarašiūnas K. , Subačius L.
Published: February 2023

Optical nonlinearities arising due to photogenerated carrier transport lead to internal space-charge electric fields which, in turn, modulate the optical properties of materials. High mobility of electrons together with the applied electric field provide much faster material response time of compound semiconductors (as GaAs, InP, CdTe) in comparison with the conventional photorefractive materials. In addition, a strong external field may introduce essentially new features of electrooptic nonlinearity due to intervalley transfer of electrons in multi-valley semiconductors. Due to a negative differential mobility μd = dv/dE <0 of hot carriers, the space charge fluctuations are not screened but grow because of a negative dielectric relaxation time τmd =εεo/(eμdn) <0 in a region of a negative differential resistance.
In vivo optical coherence tomography of human epithelium: from structural to functional imaging
Authors: Gladkova N. , Feldchtein F. , Gelikonov V. , Gelikonov G. , Petrova G. , Shakhova N. , Snopova L. , Nikulin N. , Radenska-Lopovok S. , Nasonova V.
Published: February 2023

The optical coherence tomography (OCT) technique is now rapidly advancing. To date, a large amount of actual material has been accumulated. The questions of tomograms interpretation and the place of the novel technique for imaging biotissue structures in the variety of modem diagnostic tools have become the most actual.
Temporal and spectral effects of scatterers on sub-picosecond laser-induced fluorescence of organic dyes.
Authors: Zacharakis G. , Anglos D. , Vazgiouraki E. , Papazoglou T. G.
Published: February 2023

The effect of the narrowing of the spectral distribution and the lifetime of fluorescence due to the presents of scatterers in dye solutions has already been observed. In this work we introduce the use of a streak camera and a spectrograph for the simultaneous recording of both temporal and spectral features. These experiments are part of a study on the use of scatterers in order to increase photodynamic therapy efficiency.
A Co-Crystal Containing a Merocyanine Dye, Perfectly Aligned for Electro-Optics
Authors: Spreiter Rolf , Wong Man Shing , Pan Feng , Bösch Martin , Bosshard Christian , Günter Peter
Published: February 2023

For high speed photonic applications there is a great interest for materials with large electrooptic coefficients. Due to the low dielectric constant and the mainly electronic contribution to the electro-optic effect, organic materials are especially suited. In crystals the highest possible density and best alignment of the chromophores can be achieved.
Polypyridine as an Efficient Electron-transporting Polymer for Light-emitting Diodes
Authors: Dailey S. , Halim M. , Horsburgh L.E. , Monkman A.P. , Samuel I.D.W.
Published: February 2023

A major factor affecting the efficient operation of polymer light-emitting diodes (LEDs) is the balancing of charge injection and transport in the devices. In an effort to address this issue we have investigated poly(2,5-pyridinediyl) (PPY) as an electron-transporting polymer (ETP). PPY is solution-processable from formic acid, and has excellent resistance to electrochemical[1] and photo-oxidation[2]. We synthesised PPY by oxidative coupling of 2,5-dibromopyridine with a nickel(O) catalyst[1], and the resulting material had a high photoluminescence quantum yield of 30%. We have fabricated polymer LEDs consisting of poly(p-phenylene vinylene) (PPV) as a hole transporting and emissive layer and PPY as an electron transporting layer. For comparison we have fabricated single layer devices. Figure 1a shows light-output as a function of current density for single and bilayer diodes. Figure 1b shows the electroluminescence spectrum of a bilayer device. This spectrum is similar to that of a single layer PPV diode, with an emission peak at 560 nm.
Ultra Broadband Fiber Amplifiers in 1.5~1.6μm Region
Authors: Sun Yan
Published: February 2023

The design of wavelength-division-multiplexed (WDM) systems and optical networks is currently constrained by the limited bandwidth available from erbium-doped fiber amplifiers (EDFAs). The usable bandwidth is limited to be less than 20 nm because of the highly structured gain spectrum. With gain equalization filters (GEFs), this gain bandwidth can be extended to between 35 and 40 nm. It is difficult to further increase the gain bandwidth withGEFs.
Combustion Applications of Two-Photon and Multiphoton Spectroscopy
Authors: Aldén Marcus
Published: February 2023

During the last decades laser spectroscopic techniques have emerged as the most valuable tools in characterising various combustion processes. The most important advantages of these techniques are high temporal and spatial resolution in combination with non-intrusiveness. The techniques are mostly used for temperature-, species concentration- and velocity- measurements. For a recent overview of laser spectroscopic techniques applied for combustion diagnostics, see Ref. 1.
A High Power SBR Modelocked Nd:YLF Laser
Authors: Howie C.J. , Ferguson A.L , Lee S.T. , Burns D. , Dawson M.D.
Published: February 2023

In recent years significant developments have been made in passively modelocked solid-state lasers by the application of semiconductor-based saturable absorbers1,2. Such saturable absorbers have been developed for use in broadly tunable lasers such as Ti:sapphire and Cr:LiSAF where attractive features such as improved reliability and self-starting are introduced, although at the expense of wavelength tunability compared to Kerr-Lens-Modelocked lasers.
Excited-state absorption and up-conversion losses in the Nd doped glasses for high power lasers
Authors: Landais J. , Doualan J.L. , Descamps D. , Girard S. , Moncorgé R.
Published: February 2023

Operation of a high power laser amplifier [1] made of Nd doped silicate and phosphate glasses pumped by an alexandrite laser at 782 nm has shown the existence of significant losses on the stored energy. In agreement with previous works, mostly performed on crystals such as Nd :YAG [2], Nd :LaF3 and Nd :SrF2 or glasses such as Nd :ZBLAN, these losses are mainly attributed to excited state absorption (ESA) and up-conversion (UC) energy transfer mechanisms. Simulations of population inversion starting from classical fluorescence decay and absorption measurements made as a function of pump fluence with phosphate and silicate glasses doped by 3% and 3.5% Nd ions such as LG760 and LG680 (Schott), respectively, show that an important part of the energy is lost and converted into heat by U.C. and that a non-negligible part is lost due to ESA. ESA spectra were thus systematically recorded in the pump (300-850 nm) and emission (850-1800 nm) domains of several Nd doped high power laser glasses including the above ones and others (LSG91H and LHG8 glasses from Hoya) to obtain absolute cross section values for all the relevant ESA transitions and to be able to determine the respective contributions of ESA and UC as a function of doping concentration and of pump intensity. Simulations are made by using adequate rate equations in which the ESA and emission cross sections and the overlap integrals of the corresponding spectra which are necessary to determine the energy transfer parameters are derived both experimentally and numerically with the aid of the Judd-Ofelt formalism.
Nonlinear waveguide sensor for the determination of the refractive index of liquids in the near infrared
Authors: Ramponi R. , Marangoni M. , Osellame R. , Russo V.
Published: February 2023

The knowledge of the refractive index of liquids is of major importance in many application fields and therefore several methods have been proposed to achieve high precision and accuracy. Although most methods can in principle be used both in the visible and in outer ranges (e g. in the infrared), they have typically been tested only in the visible, mainly due to experimental difficulties, and values in the infrared have been obtained by extrapolation.
Solid State Gain Media Pumped with XeCl-Laser
Authors: Kopylova T. N. , Mayer G.V. , Samsonova L. G. , Svetlichny V. A. , Kuznetsova R. T. , Sukhanov V. B. , Reznichenko A. V. , Komlev I. V. , Tavrisova M. A. , Loseva M. V. , Dolotov S. M. , Ponomarenko E.P.
Published: February 2023

Lasing properties and photostability of two dyes in both polymeric matrix and ethanol solutions radiating in blue-green region of the spectrum pumped by a XeCl - laser are studied.
Solid-state dye lasers: implications of triplet state processes to performance and towards commercial implementation.
Authors: Rahn M. D. , Golding P. , King T. A.
Published: February 2023

Solid-state dye lasers based on special glasses or plastics doped with organic laser dye molecules have the potential to provide high power pulsed laser radiation for a variety of applications, simply, cheaply and robustly[1]. As an accessory, they provide a cost-effective solution for frequency converting many pulsed lasers already in widespread use.
Continuous-wave diode-pumped Nd3+: YAG ceramics laser
Authors: Yoshida K. , Taira T. , Ikesue A.
Published: February 2023

Recently, we have developed a Nd:YAG ceramics with high optical quality [1]. The YAG ceramic allows high neodymium-ion doping to overcome low absorption cross-section. Table 1 shows the absorption coefficient of a 0.9 at.% Nd:YAG single crystal and Nd:YAG ceramics (1.1, 2.4, 4.8, and 9.1 at.%) in the 808 nm region. The 9.1 at.% Nd:YAG ceramic has about 10 times higher absorption coefficient than 0.9 at.% Nd:YAG single crystal. The laser chip was made from aYAG ceramic with 4.8 at.% Nd3+ doping level, cut to a 1.61 mm thickness. In an only polished chip Nd:YAG ceramics, single mode oscillation power of 213 mW with LD pump power of 1.6 W and a laser threshold of 334.6 mW was obtained. The slope efficiency was 17.6 %. Fig. 1 shows the longitudinal modes of the Nd:YAG ceramics laser with 200 mW output power.
High power low intensity noise single frequency light sources at 1064 nm
Authors: Zawischa I. , Knoke S. , Zellmer H. , Tünnermann A. , Welling H. , Brozek O. S. , Danzmann K. , Freitag I.
Published: February 2023

High power low noise lasers are needed in high precision interferometric gravitational wave detection In the GEO-600 gravitational wave detector a relative intensity noise of less than 10-8/√Hz and a frequency stability better than 10-3/√Hz will be required.

On power levels up to 2 W diode pumped non-planar monolithic Nd: YAG ring lasers (NPRO) are well known for their superior noise properties and their high potential for active stabilisation and intensity noise reduction [1].
Modeling of Titanium-Sapphire Waveguide Lasers
Authors: Motta Gabriella , Perrone Guido , Montrosset Ivo
Published: February 2023

Channel waveguide titanium-sapphire lasers are very attractive to build integrated broadly tunable sources. However, while the bulk configuration is well known, the feasibility of channel waveguide titanium-sapphire lasers has been demonstrated only recently[1]. In this paper we present a steady state model to study the influence of the waveguide technological parameters and find the optimum values to improve the device performances.
Coupled-Cavity Mode-Locking - Experimental and Numerical Results of a Self-Stabilizing System
Authors: Harde H. , Groninga H.
Published: February 2023

Mode-locking of lasers with coupled cavities takes advantage of the nonlinear effect of self-phase-modulation (SPM) in a nonlinear medium. A pulse from the main cavity is injected to an external cavity, where it propagates through the nonlinear medium and suffers from a phase shift as well as a frequency chirp due to SPM. When this pulse is coupled back into the main cavity, at matched cavity lengths it interferes constructively with a pulse in the main cavity at the center of the pulses and destructively in the wings. As the result of interference the pulses are shortened. In recent years this method known as additive pulse mode-locking (APM) of lasers has established to be a powerful technique for generating ultrashort pulses. This concept, first realized with the soliton laser1, generally uses an optical fiber as the nonlinear medium, and an external cavity coupled to the main cavity through one of the laser output mirrors2. This is known as the linear or Fabry-Perot type configuration. Stable APM operation generally requires an interferometric cavity length control.
Three-Ion Upconversion Processes Evidenced in the Kinetics of 4/11/2 Level in ErAG
Authors: Georgescu S. , Lupei V. , Glynn T. J. , Sheriock R. J.
Published: February 2023

A detailed analysis of the non-exponential behaviour of the kinetics of the initial laser level for three-micron generation 4I11/2, in ErAG (Erbium Aluminium Garnet) crystals (laser transition 4I11/2 →4I13/2), excited in the 4H11/2 level with short laser pulses of variable intensity, is performed. The observed non-exponentiality of the 4I11/2 decay and its dependence on the energy of the exciting pulse cannot be satisfactorily described with a rate equation modelling which includes only two-ion energy transfer processes among Er3+ ions as up-conversion from the terminal laser level (4I13/2), up-conversion from the initial one. and cross-relaxation from 4I9/2 and 4S3/2 (thermalised, at room temperature, with 2H11/2) Our analysis has shown that the inclusion of three-ion up-conversion processes from both initial and terminal three-micron laser levels leads to an excellent agreement between experimental and theoretical non-exponentiality of the 4I11/2 decay for various pumping intensities and allows the estimation of the three-ion up-conversion rates The best agreement with the experimental non-exponentialities was obtained ω111 = ω222 = 2 x 10-34 cm6s-1 and q2 = 0.9, where ω111 and ω222 represent the rates of three-ion upconversion from 4I13/2 and 4I11/2, respectively, and q2 is the ratio o two-ion up-conversio rates.
Z-scan measurements of nonlinear refraction in Yb3+: KY(WO4)2
Authors: Mikhailov V.P. , Prokoshin P.V. , Yumashev K.V. , Posnov. N.N. , Kozich V.P.
Published: February 2023

Recently, laser performance of new Yb3+: KY(WO4)2 crystal (Yb3+:KYW) has been obtained at 1025 nm [1]. The Yb3+:KYW crystal is promising for the microchip and passive mode-locked lasers tuning in the range of 1020-1060 nm. It is known that Kerr-lens mode-locking technique based on the nonlinear refractive index n2 of the laser medium itself is a manner for femtosecond laser pulse generation. Such a regime on Yb3+:KYW crystal is in progress. The efficiency of Kerr-lens mode-locking depends on the n2 magnitude, and it is very important to know the n2 of laser medium for the development of Kerr-lens mode-locking. In this paper, the nonlinear refractive index of the Yb3+:KYW crystal has been measured using the Z-scan technique with a picosecond laser pulses Using a single laser beam in a tight focus geometry one measures the transmittance of a nonlinear medium through a finite aperture in the far field as a function of the sample position z measured with respect to the focal plane. The 15-ps laser pulses having an energy of 0.45 mJ are focused into the sample to the beam waist of 80 µm Figure shows a Z-scan of a 1.5 mm thick Yb3+:KY(WO4)2 crystal which has no absorption at 1.08 µm. The curve displays positive induced changes in the refractive index, and, as consequence, positive sign of n2. The index change is calculated from the phase distortion ϕ(z,r) in the sample, which is found from fitting experimental and model curves using “Gaussian decomposition” method.
A Reconfigurable Acousto-optical Implementation of the Hough Transform
Authors: Javadpour Z. , Naughton T.J. , Keating J.G. , Rott J. , Klíma M.
Published: February 2023

The Hough transform (HT) is widely used in many pattern recognition problems to detect different features in the image by transforming each image pixel into parameter space using parametric equation of the shape to be detected. Digital techniques to implement HT require a very large accumulator memory and a large number of calculations and as such are limited to nonreal-time problems. To implement a real time transformation the massively parallel connectivity of neural network along with the high-speed, interference-free processing of optical systems can be applied[1]. Previous optical HTs were limited to the switching speed of the 2D SLM[2]. In our new implementation(Figure 1) the computation time is the aperture time of the AO cell, and is independent of the image size. Additionally there are no mechanical components, and the computation is substantially simpler than that in the other techniques.
Coherent Multipath Crosstalk due to Crossovers in an Active Splitter / Active Combiner Optical Switch
Authors: Cancela Luís G. C. , Pires João J. O.
Published: February 2023

In integrated optical space switches waveguide crossings, i.e. crossovers, become a serious issue as the network size increases. One of the most important features in designing waveguide crossings is crosstalk, which is closely related with the intersection angle between the two waveguides. In particular, crossovers imperfections along with switching elements imperfections allow that delayed replicas of the data signal reach the selected output, leading to multipath crosstalk. This phenomena has already been analysed for the Benes and dilated Benes architecture [1], but the influence of crossovers imperfections was neglected. In this paper, the influence of this interference on an Active Splitter / Active Combiner (AS/AC) architecture is considered and analysed. A relevant feature of this architecture comes from the fact that neglecting crossovers imperfections this structure becomes free of multipath crosstalk.
Nonlinear Switching in Non-Uniform Waveguide Arrays
Authors: Morandotti R. , Aitchison J.S. , Eisenberg H. , Silberberg Y.
Published: February 2023

Nonlinear directional couplers have been extensively investigated as possible all-optical switching devices. Power dependent nonlinear switching has been demonstrated in two and three-core couplers [1], and more recently, self-localization of the optical field has also been observed in a nonlinear waveguide array [2]. In this paper we report our recent experimental results with arrays of non-uniform waveguides, in which the width of one of the waveguides has been intentionally modified, giving raise to a series of novel switching characteristics.
Polarization switching mechanism in a single-mode He-Ne laser caused by injection locking
Authors: Ohta Tatehisa , Kubota Munechika , Ichinose Takumi
Published: February 2023

Polarization switching in an internal mirror 633 nm He Ne laser caused by injection locking has been reported [1]. In the present paper, the switching characteristics in single mode operation is theoretically analyzed using vectrial injection locking theory [2]. Due to an intracavity birefringence, the slave laser (SL) has two natural polarization states which are orthogonally polarized with each other and there is slight frequency difference between these polarization states for the same longitudinal mode. The frequency of the master laser (ML) is scanned uni directionally (lower to higher for example) in the following description. When the injection locking frequency range (ILER) which is proportionally depends on injection intensity is greater than twice of the above birefringent caused frequency difference (BCFD), the polarization state of SI. switches alternatively by scanning the frequency of ML as shown in Fig. 1. If the ILER is less than the BCED, ILFRs of both polarization states do not overlap and the polarization switching does not occur. In the case of BCED < ILFR < 2 × BCFD, the polarization state of lower frequency switches to that of higher frequency, however polarization switching of reverse direction does not occur as shown in Figs. 2 (a) and (b). The calculated results are well agreed with the experimental results.
CCD based low-coherence interferometry using balanced detection
Authors: Podoleanu Adrian Gh. , Seeger Mauritius , Jackson David A.
Published: February 2023

The detection of reflective interfaces in a multilayer object using Coherence Radar [1] is limited by the dynamic range of the analogue CCD camera and the analogue to digital (A/D) converter or frame grabber [2]. In this paper, we describe a new differential detection method for Coherence Radar which significantly reduces the required dynamic range of the A/D converter.
Trace Element Analysis of Cast Uranium Metal Using Laser-Induced Breakdown Spectroscopy
Authors: Young James , Botheroyd Iain M , Whitehouse Andrew I
Published: February 2023

The technique of laser-induced breakdown spectroscopy has been successfully applied to the analysis of trace elements within cast uranium metal fuel, used within Magnox nuclear reactors. This form of optical emission spectroscopy is particularly suited to direct solids analysis, where on-line and near real-time measurements are required [1].
SPICE-Aided Design of Low Threshold, Wide Bandwidth 1.55 µm Strained MQW Lasers
Authors: Rossi G. , Bertone D. , Fang R.Y. , Meliga M. , Morello G. , Paoletti R.
Published: February 2023

Carrier transport properties have been demonstrated to strongly affect the static and dynamic behavior of quantum well lasers [1]. We have developed a tree level rate equation model (figure 1), which treats each well independently, in order to distinguish between space and state transport and to take nonuniform injection and carrier dependent gain for each well into account. Starting from the level scheme reported in figure 1, a complete set of rate equations can be derived and implemented on a SPICE circuit emulator thanks to their formal analogy with current balance equations at a capacitor node. By using SPICE, static and dynamic simulation can be run without any change in the model. The active region simulation can be integrated as well with parasitic, package equivalent circuit and other electrical components. Model parameters have been extracted from measurements on real devices. The model has been used to analyze the device behavior, identifying P-I curve bending in short devices as an heterojunction leakage effect (less efficient capture at higher injection currents). An improvement was found changing the number of wells: figure 2 shows the optimum well number, that gives the best static properties. Similar investigations have been done concerning the modulation bandwidth, suggesting the use of a larger number of wells. On the basis of these results we have grown structures with different well numbers (5, 9, 13 and 17 wells) using MOCVD (Metallo Organic Chemical Vapor Deposition). Wells were compressive strained (+0.9%) and barriers were tensile strained (0.5%) and respectively 8 and 9 nm wide. Threshold current densities of broad area lasers were measured, showing an optimum number of well around 9 (figure 3). Using this last structure Semi Insulating Buried Heterostructure Fabry-Perot laser have been then realized, obtaining 6-8 mA threshold currents, up to 22% external efficiency and very good temperature behavior. Due to parasitic effects the bandwidth was limited to 15 GHz. The intrinsic material bandwidth was then evaluated both by direct measurement with optical modulation, and by analytical processing of electrical bandwidth. As reported in figure 4, both ways lead to the same result which is an intrinsic material bandwidth in excess of 20 GHz.
Sub-15-fs Pulses at 1.5 µm by Parametric Generation
Authors: Nisoli M. , Stagira S. , De Silvestri S. , Svelto O. , Valiulis G. , Varanavicius A.
Published: February 2023

Ultrashort high-energy pulses tunable In the infrared are strongly needed for applications in nonlinear optics and spectroscopy. Sub-100-fs infrared pulses were achieved by traveling- wave optical parametric amplification (OPA) [1-3]. The generation of multi-gigawatt sub-20- fs pump pulses, obtained by the hollow-fiber compression technique [4], offers the possibility to investigate parametric processes in an ultrashort temporal regime.
Femtosecond Pulse Compression by Second-Harmonic Generation in Aperiodically-Poled KTP
Authors: Reid D. T. , Loza-Alvarez P. , Ebrahimzadeh M. , Sibbett W. , Karlsson H. , Laurell F.
Published: February 2023

By fabricating a periodically-poled frequency-doubling crystal with a linearly-varying grating period one can define the position in the crystal at which any frequency is converted to its second harmonic. Using this method stretched pulses from an erbium-doped fibre laser were recompressed in aperiodically-poled lithium niobate [1]. In our work we describe the use of an aperiodically-poled crystal of KTP [2] to frequency-double and compress the chirped femtosecond output pulses from an optical parametric oscillator (OPO) running at a wavelength of 1.25 µm.
“Comparison of radiation characteristics of lasers equipped with ordinary stable resonator and resonator with “cat-eye” type mirror”
Authors: Dimakov S. , Habich U. , Kliment'ev S. , Orlova I. , Wolf N.
Published: February 2023

Comparison of experimental results of output characteristics of the laser RS-5000 equipped with an ordinary stable resonator and a resonator with "cat-eye" type mirror (reflector) is presented in this report.
Efficient Wavelength Conversion with High Power Passively Q-Switched Diode-Pumped Neodymium Lasers
Authors: Agnesi A. , Dell'Acqua S. , Piccinini E. , Piccinno G. , Reali G.C.
Published: February 2023

High average power compact sources of nanosecond pulses at kilohertz repetition rate are interesting for many practical applications, each requiring a specific operating wavelength. Cr:YAG solid-state saturable absorbers recently proved to be particularly attractive for the development of compact high-power Q-switched diode-pumped lasers1,2.
High Average Power, High Pulse Repetition Frequency Diode Pumped UV Solid-State Laser System
Authors: Koch R. , Schröder Th. , Stamm U. , Zschocke W. , Basting D.
Published: February 2023

We have demonstrated significant extension of the pulse repetition frequency (PRF) operation regime of a diode-bar-pumped Nd:YAG laser towards higher PRF. The laser is an electro-optic Q-switched Nd:YAG laser with stable resonator It is side-pumped by pulsed laser diodes with a duty cycle in the order of 20 %. Earlier we have demonstrated that the PRF can be continuously adjusted over an enormous range from 1 Hz to 1 kHz At 1 kHz, typically an output power of 10 W is generated, corresponding to a single pulse energy of 10 mJ [1]. The pulse duration in the fundamental wave is about 12 ns. Combined with a near-diffraction limited beam quality (M2 < 1.1), this high intensity allows external harmonic generation with high efficiency. Typical values at 1 kHz are an average power of 6.5 W at 532 nm, 4.5 W at 355 nm, 2.8 W at 266 nm, and 1 W at 213 nm in the 5HG [2].
High Power Fibre Optic Laser Beam Delivery
Authors: Booth H. J. , Webb C. E. , Whybrew A.
Published: February 2023

The delivery of high peak power laser beams via optical fibres is important for many practical applications where it is advantageous to site the laser remotely from the work station. Beam delivery using small core optical fibres is particularly important in micromachining applications where beam handling flexibility is required. However, at high peak powers, the alignment of the optical fibre with respect to the laser beam is critical and small misalignment can easily lead to damage at the input face of the optical fibre. We report a new technique for efficient high power fibre optic laser beam delivery which is stable, self aligning and minimises the chance of damage to the input face of the fibre.
Single-Mode Operation of Laser Diode Arrays Using Photorefractive Phase Conjugators
Authors: Petersen Paul M. , Løbel Martin , Johansen Per M.
Published: February 2023

Lasers using phase conjugate feedback have many attractive properties such as aberration correction, generation of short mode-locked pulses, and diffraction limited high brightness output. The phase conjugate feedback, however, may also lead to unstable behavior with period doubling instabilities and optical chaos1.
Optical Phase Conjugation Using Four-Wave Mixing in Laser Diodes Subject to Strong Probe Injection Power
Authors: Hong Y. , Tang J. M. , Shore K. A
Published: February 2023

Optical phase conjugation through nearly degenerate four-wave mixing (NDFWM) in semiconductor lasers has attracted considerable attention in recent years since being first demonstrated by Nakajima and Frey[ 1 ]. Such interest arises due to the very high conjugate reflectivity of order 30-40dB which can be achieved owing to the amplifying effect of the semiconductor gain medium and cavity enhancement of mixing process. However, most previous experimental and theoretical work has placed emphasis on the weak signal case, where the injection signal acts only as a small perturbation of free-running laser diode. It is only very recently that a theoretical analysis of NDFWM in a semiconductor laser subject to strong probe injection power has been presented[2].
Based on InAs Fast and Highly Efficient Phase Conjugate Mirror for The Repetition-Rate CO2 Laser Radiation
Authors: Bulaev V.D. , Vidavskii A.E. , Kovalev V.I. , Kulikov V.V.
Published: February 2023

The ability of a pulsed laser to ran in a repetition-rate (RR) regime is an important demand to that one dedicated to operate in industry etc. For a pulsed CO2 laser the vast majority of the problems in design the appropriate systems are solved already. Among the unsolved problems one is the poor beam divergence of their radiation. The dynamical optical nonuniformities of the active medium of such lasers is the primary cause of this.
An Optical Fibre Instrumentation System for Pressure and Temperature Measurement in Oil and Gas Wells-From Design to Installation and Operation
Authors: Eriksrud M. , Nakstad H.
Published: February 2023

The Fibre Optic Well Monitoring (FOWM) system performs permanent downhole measurements of pressure and temperature. The system has no electronic components downhole and is based on a resonating silicon micro-machined structure, which is excited and interrogated optically through an optical fibre. By using passive optical sensors downhole and optical fibre communication, much of the system complexity can be removed from the harsh downhole environment and brought to the more benign seabed or production platform environment. This results in a reliable system even for high temperature operation.
Long-period grating interrogating FBG strain sensor achieving a combination of large dynamic range and high resolution
Authors: Fallon R. W. , Zhang L. , Bennion I.
Published: February 2023

In this paper we describe an optical strain sensing system using a long-period grating interrogating a FBG (fibre Bragg grating) strain sensor to achieve both large dynamic sensing range and high resolution. The complete system is shown in figure 1. The reflected light from the FBG is incident on a long-period grating which acts as an edge filter. The light transmitted by the long-period grating increases (or decreases depending on which side of the long-period grating is in filtering) with the strain-induced wavelength shifting of the FBG. The reference arm is required to linearise the power-strain response as the spectral distribution of the Er fibre light source is non-uniform, and compensates any fluctuation in light source. The FBG had its peak wavelength at 1519nm. The long-period grating had a 20nm transmission peak centred at ~1529nm with a rejection ratio of 22dB. The filter shows a near-linear response of ~ 1.8dB/nm allowing an unambiguous sensing range of 10nm, equivalent to ~10 000µε.
Ultrafast Technology in Communications
Authors: Knox Wayne H.
Published: February 2023

As optical communications evolve in capacity, complexity, bandwidth and density, there are increasing opportunities for novel technologies to contribute. Ultrafast technology (capable of generating pulses of 100 fs or shorter duration) can be used in ultra-high speed Time Domain Multiplexed systems, with data rates as high as 640 Gb/s [1]. Ultrahigh speed TDM can be transmitted over a limited number of wavelength channels (TDM in Figure 1). Alternatively, WDM systems with Tb/s capacity and greater can be constructed by using lower TDM rates with many WDM channels using 100 or more conventional DFB laser diodes [2]. A new scheme for WDM systems has been recently developed using highly chirped pulses (CPWDM in Figure 1) [3], and Code-Division multiplexing (CDMA in Figure 1) has been demonstrated using femtosecond optical pulses and a nonlinear discriminator [4].
Air Force 1-GBPS space-borne optical communications system
Authors: Barry James D.
Published: February 2023

A pioneer Nd:YAG laser communication system operating at 1000 Mbps is scheduled for test in 1979 as a synchronous altitude satellite to ground data link. The system will be a transmitter operating at λ532 nm from a 20-cm diam telescope to a ground station at Cloudcroft, N.M. Laser communications has progressed from component development 5 years ago to the recently completed engineering feasibility model which demonstrated space applicability. The visible laser system was successfully tested to the component and system vibration and thermal flight acceptance specifications of the defense meteorological satellite program.
Performance and growth potential of CO2 laser space communication systems
Authors: Goodwin F. E. , Henderson D. M. , Nussmeier T. A. , Stokes L. S.
Published: February 2023

The historic trend in satellite communications has seen communication bandwidth utilization increasing 3 orders of magnitude per decade. This trend points toward common usage of gigabit per second data rates in the 1980s. Mission constraints and requirements lead to the conclusion that the most efficient means of transmitting such data from a satellite in low earth orbit to a single earth station is a laser data link through a geosynchronous relay satellite. The laser link is attractive because of its small antenna size and competitive power and weight compared to rf systems.