bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Fibre Parameters Measurement Using Modulation of the Spectrum of A Low-Coherence Source
Authors: Hlubina Peir
Published: February 2023

It has been predicted theoretically [1-2] and confirmed experimentally [3] that the mutual interference of modes of a two-mode, weakly guiding, step-index optical fibre leads to a variable modulation of the source spectrum when the source coherence length is shorter than the optical path difference (OPD) between modes. In this contribution, this effect, which means that the mutual interference of modes of an optical fibre occurs no matter how long or short the OPD between modes may be. is demonstrated experimentally al the output of a weakly guiding, step-index optical fibre excited by a low-coherence source whose central wavelength is below the cut-off wavelength of a single-mode regime. As an example, a weakly guiding, step-index optical fibre of length z= 1.76 m having a cut-off wavelength of 920 nm and a core diameter of 4 μm is excited at a wavelength of 671.6 nm by a low-coherence source whose coherence length is 280 μm. The intensity distribution corresponding to two lowest-order linearly polarized (LP) modes is resolved at the output of the optical fibre and no mutual interference between both LP modes is observed. Fortunately, it has been confirmed experimentally (see both figures) that the spectral interference between both LP modes is present
Axicon-type test interferometer for cylindrical surfaces
Authors: Brinkmann S. , Dresel Th. , Schreiner R. , Schwidet J.
Published: February 2023

Interferometric testing of technical surfaces makes a reduction of the sensitivity necessary to deal with the rather big surface deformations and the micro-roughness due to the machining process. Therefore, grazing incidence interferometry is commonly used for planar work pieces. Here we report on the testing of cylindrical surfaces which makes use of computer generated holograms having cylindrical symmetry as beam splitters and recombining elements. The principle of the interferometer has been invented earlier/1/ and is given in Fig. 1. The collimated light beam from a laser impinges onto the first axicon-CGH and generates a first diffracted order which is reflected from the work piece and hits a second axicon CGH which combines the two beams reflected from the object and the undiffracted light of axicon 1 and 2. An ideal cylinder will result in a zero fringe field. All deviations from cylinder symmetry will be indicated through fringe distortions. Due to the diffractive axicons the deviation by one fringe corresponds to a surface deformation perpendicular to the surface of half a period of the axicon line pattern. In this way it is extremely simple to adapt the sensitivity of the interferometer to the technical needs. The deviations of the objects are somewhat screened by alignment aberrations.
Microwave-Optical Mixing with a Frequency Modulated Laser and an Unbalanced Mach-Zehnder
Authors: Maury G. , Cabon B.
Published: February 2023

Using optical techniques to undertake microwave signal processing is a new step in the evolution of optoelectronic technologies. Thus, mixing microwave frequencies using all optical components has many applications in communication systems with fiber-optic links. Different mixer configurations using electrooptic modulators have already been studied [1], [2], but they all present very large conversion loss. We report here simulation results of a mixer configuration using a passive optical device. A low conversion loss is demonstrated.
A new integrated all-optical switch based on a micro-cavity
Authors: Blom F.C. , Hoekstra H.J.W.M. , Driessen A. , Popma Th. J. A.
Published: February 2023

Integrated all-optical switches [1] can be of great importance for optical transparent telecommunication network. All-optical switching is based on the phase change of the light due to the intensity in nonlinear optical (NLO) materials. The materials investigated up to now exhibit NLO coefficients which are still too low for realistic high speed devices performance at low optical power. A possible way to improve the NLO is enhancement of the electric field inside the material using micro-cavities. Recently, rotationally symmetric dielectric micro-cavities with radii larger than the wavelength are modelled theoretically for linear and NLO materials. These micro-cavities can confine large electromagnetic fields in small volumes and act as optical cavities with high quality factors (Q’s >104 [2]). Examples of these micro-cavities are semiconductor microdisk lasers and Nd:YAG spherical lasers. All kind of NLO processes, such as stimulated Raman scattering and sum-frequency generation, have already been reported for liquid droplets, however, in integrated optic devices micro-cavities have not yet been used. The spatial distribution of the internal field in the cavity is in general dominated by the near resonance-mode, the whispering gallery mode, when the incident frequency is near one of the high-Q modes, ω0.
Kilohertz generation of picosecond pulses at 1.57 μm using optical parametric generation and amplification
Authors: Greiner U. J. , Schröder T. , Klingenberg H. H.
Published: February 2023

Only recently researchers started to investigate the frequency conversion of high power picosecond pulses produced by regenerative amplification1. The high power densities easily achieved with short, pulses allow efficient generation of parametric fluorescence. However, experiments show that the efficiencies achieved in these systems are not as high as one would expect from a simple calculation, due to the temporal and spatial pulse shape, which has to be considered in a reasonably accurate model2,3. We performed calculations on the efficiency of the parametric conversion for various temporal and spatial pulse profiles and for different arrangements of a picosecond optical parametric generator (OPG) and optical parametric amplifier (OPA) combination. In the numerical simulation and the experiments we used a KTP crystal pumped with the fundamental of an all-solid-state Nd:YAG regenerative amplifier.
CW synchronously pumped optical parametric oscillators in periodically poled LiNbO3
Authors: Butterworth S. D. , Pruneri V. , Hanna D. C.
Published: February 2023

Periodically-poled LiNbO5 (PPLN) has considerable attractions as the nonlinear medium for optical parametric oscillators (OPOs). These include its large nonlinearity (deff -20/pm/V), the ability to quasi-phase-match non-critically for any wavelengths within its transmission range (extending to near 5μm), and its reduced susceptibility to the photorefractive effect.
A 6.2 kHz Pulse Repetition Rate Ce3+:LiLuF4 Laser Pumped by a Frequency Doubled Copper Vapour Laser
Authors: Coutts D. W. , Cashmore J. S. , Webb. C. E.
Published: February 2023

There has been considerable recent progress in the operation of tunable uv solid-state lasers based on trivalent cerium doped fluoride crystals1-2, most notably Ce.LiCAF, Ce:LiSAF and Ce:LiLuF. To date most reported operation has been restricted to below 10 Hz pulse repetition frequency (PRF), partly due to restrictions in the operating PRF of the pump laser (KrF excimer or frequency quadrupled Nd:YAG). Frequency doubled copper vapour lasers3 (CVLs) operate al kilohertz PRFs (4-24 kHz) and can produce three uv wavelengths namely: 255 nm (second harmonic of the CVL green). 289 nm (second harmonic of the yellow) and 271nm (sum-frequency). These uv wavelengths efficiently access the pump bands for Ce3+ doped fluoride crystals, in particular 271 nm corresponds to the peak of the σ-polariscd absorption in the LiCAF and LiSAF hosts, and 289 nm matches the absorption peak for LiLuF. In all cases, these pump wavelengths are longer than those employed to date for cerium doped solid stale lasers, thus potentially minimising the formation of transient and permanent colour centres that often limit performance at high PRF. As well as high PRF operation and uv wavelength flexibility, the frequency doubled CVL also offers high beam quality tor efficient longitudinal pumping geometries.
Single-beam emission from surface-emitting laser diodes based on surface mode emission
Authors: Köck A. , Golshani A. , Hainberger R. , Finger N. , Gmachl C. , Gornik E. , Korte L.
Published: February 2023

We present strongly improved results from optimized surface emitting laser diodes, which are based on a surface mode emission (SME) technique. This technique has been developed by us and can be applied to conventional horizontal cavity laser diodes to achieve an efficient surface emission with low beam divergence as well as a quasi-single-mode operation1. It is based on a coupling process between the laser mode and a TE0-surface mode propagating in a waveguide structure on top of the laser diode.
Resonant Waveguide - Grating Structures
Authors: Friesem A. A. , Rosenblatt D. , Sharon A. , Agrawal N. , Engel H. , Steingrueber R. , Weber H.G.
Published: February 2023

Under certain conditions, a resonance phenomenon can occur in waveguide-grating structures. Such structures have multilayer configuration, the most basic of which is comprised of a substrate, a thin layer dielectric or semiconductor waveguide layer, and an additional transparent layer in which a grating is etched. The resonance phenomenon is based on the interaction of light diffracted by the grating and light propagating through the waveguide. Specifically, when such a structure is illuminated with an incident light beam, part of the beam is directly transmitted and part is trapped in the waveguide layer. Some of the trapped light is then rescattered outwards, so that it interferes destructively with the transmitted part of the light beam. At a specific wavelength and angular orientation of the incident beam, the structure “resonates”; namely, complete interference occurs and no light is transmitted. The bandwidth of the resonance is based on several parameters, such as the grating depth and duty cycle, as well as the thickness of the waveguide layer.
Fringe Phase Encoded Joint Transform Correlator
Authors: Wang Ruikang K. , Shang Lin , Watson Ian A. , Scott B.F.
Published: February 2023

In the image reconstruction and restoration techniques, the phase information is found to be considerably more important than the amplitude information, which thus leads to the invention of the phase-only filtering in the VanderLugt correlator arrangement. The joint power spectrum (JPS) in the joint transform correlator (JTC), can be viewed as the interference fringe between the reference and input scene modulated by the cosine of the fringe phasors1. The phase difference between the reference and the target is carried by the fringe carrier determined by the separation between the reference and the target. This paper investigates the performance of the joint transform correlator which encodes the fringe phases of the JPS onto a phase SLM to the input of the second optical set-up.
Vector Phase Conjugation in Saturable Media
Authors: Green R. P. M. , Syed K. S. , Camacho-Lopez S. , Damzen M. J.
Published: February 2023

Vectorial phase conjugation (VPC) is an effective way of eliminating both phase and polarisation distortions in optical systems and is of special interest in solid-state amplifiers operating at high average powers in which the amplified radiation can become depolarised. There have been experimental demonstrations of VPC in two-photon resonant media and in media with local response [1,2]. This paper presents experimental results of the phase conjugate reflectivity and fidelity of VPC in saturable media (Cr4+:YAG and inverted Nd3+:YAG).
Fiber Phase-Conjugators at 1.06μm Wavelength
Authors: Eichler H.J. , Kunde J. , Liu B.
Published: February 2023

Using stimulated Brillouin-scattering (SBS) in glass fibers as phase-conjugating process, the field of application of SBS phase-conjugators [1,2] can be expanded, because fibers offer a decreased power threshold and a stable behaviour even at high input energies. Furthermore, the damage threshold of the fiber lies above 500MWcm−2. Figure 1 shows the experimental set-up for our investigations.
Diode Pumped Thin Disk High Power Yb Lasers
Authors: Giesen A. , Brauch U. , Johannsen I. , Karszewski M. , Stewen C. , Voss A.
Published: February 2023

We present our results obtained with diode-pumped Yb:YAG thin disks showing the promising potential of the thin disk laser concept for high-power applications with highest beam quality (TEM00 duo or even single frequency)
Improved Yb-doped fluoride phosphate laser glasses with optimized local structure
Authors: Seeber W. , Ehrt D. , Danger T. , Heumann E. , Mix E. , Huber G.
Published: February 2023

The favorable laser properties of Yb-doped earth alkaline fluorapalite crystals (FAP) have been demonstrated [1]. Fluoride phosphate (FP) glasses are a kind of amorphous analogon to these both fluoride and phosphate anions containing crystals. It could be shown that Yb-doped FP-glasses have the potential for cheap diode pumped cw-lasers acting at wavelength around 1.04 μm at room temperature (2). In first experiments using laser diodes emitting at 968 nm (longitudinal pumping geometry, hemispheric resonator with an output mirror of r = −5 cm radius of curvature, T = 2 %) and not optimized FP-glasses we achieved maximum output powers Pout of about 145 mW and absorbed pump powers at thresholds Pthr,abs of about 185 mW. Recently, experiments with optimized glasses demonstrated improved laser performance (up to Pout of about 220 mW;Pthr,abs ~106 mW) [3]. Similar to DeLoach et al. [4] we trace the surprisingly good laser parameters to the special energy level structure of the 2F7/2:Yb ground manifold in the mentioned materials. The laser transition terminates at an electronic Yb-level (about 600 cm−1 above the ground state) interacting with the local vibrational modes of localized Yb-O bonds. The huge variety of FP-glass compositions provides a useful tool to tailor the local structure at the site of the Yb-ion and in this way the electron-phonon interactions itself. To optimize the host glass matrix we used the following simple structural model: Yb3− ions are mostly six co-ordinated in the investigated FP-glasses. Three PO43− (phosphate)-tetra-hedra form a cluster with D3-symmetry about the Yb ion. So-called v4-vibrations of the surrounding phosphate groups (~ 570 cm−1) can interact with the electronic Yb-transition. The addition of heavy ions (e.g. Ba) and other tetrahedral groups (e.g. SO42−) to batch composition: 95 mol-% (AlF3 earth alkaline fluorides) - 5 mol-% Sr(PO3)2 strongly improves the laser properties. This can be explained by formation of [Yb(PO4)3]-clusters which are nearly isolated from the mainparts of the network. Because of the inhomogeneous site variation in glasses no detailed structures in the absorption spectra could be observed even at low temperatures. Nevertheless, the corresponding terminal laser level (~ 600 cm−1 at high pump power densities) supports the assumption of efficient electron-phonon coupling. The intensity borrowing effect by this mechanism can be understood in terms of a electron-vibrational coupling constant [4], but the direct influence on the laser properties itself is not yet understood. We believe that the electron-phonon coupling efficiently depopulates the terminal laser level too. In conclusion, efficient cw-laser action in optimized FP-glasses can be traced to nearly isolated [Yb(PO4)3]-clusters with effective electron-phonon coupling.
Long Fibre Grating Characterisation using Low Coherence Reflectometry
Authors: Volanthen M. , Geiger H. , Cole M.J. , Laming R.I. , Dakin J.P.
Published: February 2023

Optical fibre dispersion compensation,[1] and distributed fibre sensors,[2] make use of long fibre gratings. Their reflectivity and lime delay are usually characterised as a function of wavelength using an expensive tunable laser.[3],[4] We have recently achieved similar results with a new low-cost low-coherence reflectometry technique, which is related to earlier techniques for optical fibre characterisation.[5]
Narrow linewidth, High Power Q-switched Erbium doped Fibre Laser
Authors: Lees Gareth P. , Cole Martin. J , Newson Trevor P.
Published: February 2023

For distributed temperature sensing based on Brillouin scattering, narrow linewidth pulsed sources are required to spectrally resolve the Rayleigh and Brillouin backscattered radiation. The temperature is determined by the relative intensity of the Rayleigh and Brillouin backscattered light i.e the Landau-Placzek ratio[1]. Typically the backscattered Brillouin is separated from the Rayleigh by about 10 GHz A Q-switched fibre laser using a narrowband in-fibre Bragg grating as an output coupler ensures the Q-switched laser operates with a narrow linewidth, whilst the Q-switched operation produces the high power pulses necessary to produce a stong back-scattered Brillouin signal. Figure 1 shows the optical arrangement used for the Q-switched laser.
A Passive Fibre Optic Sensor for Detection of CO2 at 590 nm
Authors: Watson Ian A , Wang Ruikang K , Chye Tay B
Published: February 2023

Industrial applications of fibre optic sensors have been limited to situations where they provide technical advantage (1) over conventional sensors. This has primarilily been due to their significantly higher costs and the reluctance of industry to depart from tried and tested technology. In the present case an inexpensive, passive, fibre optic sensor was fabricated to monitor concentrations of CO2 gas with applications ranging, for example, from the medical to food processing industries. By selection of appropriate materials the technique can be extended to detect a range of acidic or alkaline gases. Because the operating wavelength is 590 nm. the fibre optic sensor can be used remotely at greater distances than fluorescence based fibre sensors which operate in the UV and have high fibre losses. Moreover, these sensors are: easy to implement, cost effective, insoluble in water, unaffected by relative humidity, and do not need covering with a diffusion membrane.
Photopumped Infra-Red Vertical Cavity Surface Emitting Laser
Authors: Hadji E. , Bleuse J. , Magnea N. , Pautrat J.L.
Published: February 2023

Vertical cavity surface emitting laser (VCSEL) have been extensively investigated due to their attracting properties (emission through the surface, single longitudinal mode operation, circular beam profile….) They have also stimulated many fundamental studies designed to understand how to couple the major part of the spontaneous emission in the lasing mode, and in order to reach a thresholdless (or near thresholdless) laser.
Calcite Frequency Splitter For High-Density Wavelength-Division-multiplexing Transmission
Authors: Breviario Fabio , Pietralunga Silvia , Martinelli Mario , Di Rocco Daniele
Published: February 2023

In this work we present a frequency demultiplexing device, inserted in a multimode transmitting stage for High Density WDM systems. It is based on bulk Calcite single crystals and represents a valuable and cost-effective alternative solution to dispersive gratings and Fabry-Perot filters in separating closely spaced optical channels.
Thermal Stability of Uniform-Period, Chirped, and Bandpass Fibre Grating Structures Fabricated in Hydrogenated Optical Fibres
Authors: Zhang L , Fallon R W , Sugden K , Bennion I
Published: February 2023

We report the results of detailed investigation of the thermal stability of UV side-written ultra-strong fibre gratings by isochronal annealing at temperatures up to 775°C. For the first time, we compare the properties of saturated uniform-period, chirped, and resonant bandpass structures fabricated in hydrogen-loaded fibres of several types, including standard telecommunications fibre, and high-Ge and B/Ge codoped fibres.
Fully Stabilized, 10 GHz Soliton Fiber Laser
Authors: Cristiani I. , Marazzi L. , Franco P. , Fontana F. , Vidmar M. , Midrio M. , Romagnoli M.
Published: February 2023

The development of high bit rate laser sources has attracted much interest in view of its application in fiber transmission systems One of the most interesting devices are the harmonically mode-locked fiber lasers (HML-EDFL), because of their intrinsic property of generating hyperbolic secant or gaussian pulse trains, suitable for soliton transmission systems. The most important characteristics of this source are wide tunability (more than 50 nm in the 1550 spectral region [1]), repetition rate up to 40 GHz [1] and pulse duration down to a few picosecond. In view of the application of this source in a commercial transmission link, few problems require to be solved: the control of the state of polarization of the light circulating inside the cavity, the stabilization of the modulation frequency, and the cavity pulse filling.
Varied Spectral Properties of Annealed Dispersive Fibres
Authors: Nishimura Junji , Morishita Katsumi
Published: February 2023

Optical fibres made from core and cladding materials with different dispersions are proposed theoretically to get optical fibre devices that have not yet been achieved by conventional fibres [1]. The fibres are called dispersive fibres due to their large wavelength dependence of the index difference. Dispersive fibres arc fabricated from optical glasses whose refractive-index curves interseet [2]. However, it is difficult to make dispersive fibres with various chromatic characteristics because of limited number of optical glasses. In this paper, it is shown that spectral properties of dispersive fibres can be changed greatly by annealing under the proper conditions.
unconventional modes of laser resonators
Authors: Kerméne V. , Colombeau B. , Desfarges A. , Devilder P. J. , Froehly C. , Ménard S. , Vampouille M.
Published: February 2023

We propose and demonstrate an original modal filtering process able, in some cases, to induce convergence of laser field distributions towards an unique and unconventional modal profile thanks to two appropriate filters in two intracavity planes for which the transverse fields are connected by a Fourier Transform. The two different and complementary filters were designed in order to induce pattern dependent diffraction losses in both Fourier planes of the cavity.
8×8 Database Filter Array Chip Fabricated with Field Effect Transistors and Vertical Cavity Surface Emitting Lasers
Authors: Hayes E.M. , Snyder R.D. , Jurrat R. , Stanko P.J. , Feld S.A. , Wilmsen C.W. , Choquette K.D. , Geib K.M. , Hou H.Q.
Published: February 2023

In order to compete with electronic solutions, parallel optical signal processing & computing require large smart pixel arrays that arc fast, reliable, and reasonably priced with uniform performance across the array. To meet all of these qualifications requires the use of a well developed foundry. This paper presents the design and experimental results of an 8×8 array of GaAs smart pixels in which the high speed input photodetectors, logic gates and output driver are monolithically integrated and fabricated by a foundry. Each pixel of the array is made up of three MSM photodetectors, one AND and one XOR logic gate composed of enhancement mode MESFETs and one four stage laser driver with bump bonding pads, all fabricated by Vitesse through the MOSIS foundry. Vertical cavity surface emitting lasers (VCSELs) will be flip chip-bump bonded to the completed Vitesse fabricated chips using a coplanar contacting technique similar to the one developed by Goossen et al. [1]. This technique allows the VCSELs to be stand alone devices embedded in each pixel and not occupy space remote to the optical processors, thus saving space and reducing interconnect capacitance. In addition, as the array size becomes large, electrically connecting the pixels with the remotely placed output devices becomes difficult and defeats the purpose of the optical interconnects.
Scalability Issues in WDM All-Optical Networks
Authors: Blumenthal Daniel J.
Published: February 2023

All-optical photonic networks oiler the potential for bit-rate and format transparent communications. In this class of network, signals traverse the network without oplo-electronic conversion at the routing nodes and may encounter multiple liber links, multiple routing and regenerative components, and signals transmitted on other wavelengths. Due to the analog nature of these networks, the network capacity in terms of number of wavelengths and bit-rate per wavelength that can be supported will depend on the characteristics of the devices and the network they are embeded in. This limitation comes about from a complex interaction between the network architecture and its physical implementation and can lead to degradation in signal-tonoise-ratio and the usable optical bandwidth. Physical limitations that must be considered include bandwidth of the fiber and components, interchannel crosstalk (between wavelengths) due to nonlinearities in the optical fiber and optical amplifiers, incoherent and coherent interchannel crosstalk, and optical and electronic noise.
Laser Projector Technology
Authors: Deter Christhard , Kraenert Juergen
Published: February 2023

The laser projection technology has a number of advantages in comparison to the classical light projector principles. In contrast to lamp projectors it is not necessary to realize the non efficient spectral splitting of RGB colour parts. The divergence of the laser beam make the reduction of aperture effects possible and allows to enhance the lumen efficiency.
Evaluation of (In,Ga,As)P-Based Materials for Use in Fabry-Perot Modulator Applications at Low Temperatures
Authors: Tang C.F. , Whitehead M. , Stavrinou P.N. , Glick M. , Parry G. , Button C.C. , Hill G.
Published: February 2023

It is now common in applications requiring large bandwidth to transport data using optical links; thereby replacing conventional electrical wiring. The electro-optical interface element in such an optical link could be a semiconductor laser or electroabsorption modulator. At present it is routine to design such devices for room temperature operation. However we can envisage applications requiring devices to work in low temperature environments; for example, in particle colliders, magnetic resonance imaging scanners, supercomputers, infra-red detectors, etc.
High-Speed Performance of Quantum Well Infrared Photodetectors
Authors: Ershov M. , Ryzhii V.
Published: February 2023

Quantum Well Infrared Photodetectors (QWIPs) are intrinsically high-speed devices. Recent experimental studies showed that QWIP’s response time lies in the picosecond range [1,2]. The measured response time was limited by parasitic elements [1]. The high-frequency capability of QWIP’s was demonstrated in a heterodyne experiments with a 3-dB bandwidth of about 20 GHz [2]. Potential applications of high-speed QWIP’s are in wideband CO2-laser-based spectroscopy, communications, and radar. At present, there is no clear understanding of what physical mechanisms are responsible for QWIP’s response. Several mechanisms, including carrier drift and capture into the QWs, have been proposed, without rigorous theoretical justification. In this paper, we study the high-speed performance of of QWIPs using numerical modeling.
Fabrication of Silicon Microlenses
Authors: Eisner M. , Schwider J.
Published: February 2023

Melting photoresist cylinders is an often described /l/ and effective method to produce microlenses. One of the possible application areas is optical communications where they serve as coupling elements between the light source and the fibre or between the fibre and the detector. In optical communications single mode fibres are preferred because of the absence of mode dispersion and mode noise. For this case the working wavelength lies in the infrared frequency band (e.g. 1300nm) and so resist lenses are not suited because of their high absorption coefficient. One possible solution is the use of silicon microlenses which can be obtained by reactive ion etching (RIE) of the resist lenses. In order to get well defined lenses an extensive study of the each parameters is necessary. The melting process of resist cylinders produces nearly ideal spherical lenses because of the surface tension. A “one to one" copy by RIE of such resist lens into silicon is not possible. Apart from die fact that it is difficult to obtain a selectivity of 1:1 between resist and silicon which would guarantee equal heights of resist and etched lens the main reason for this behaviour is the specific etch mechanism of the RIE. The etching process is of a chemical nature supported by ion bombardment.
Effect of gamma radiation on performance of Cr, Tm, Ho: YAG and Er: YAG lasers
Authors: Kaczmarek S. , Mierczyk Z. , Kopczyóski K. , Matkovsky A.O. , Sugak D.Yu. , Durygin A. N. , Frukacz Z.
Published: February 2023

It is well-established that color centers (CCs) produced by ionizing radiation or short-wave radiation of the pump lamp, strongly influence the optical characteristics of yttrium-aluminium garnet single crystals [1-4], However, the possibility of positive effect of ionizing radiation on optical output of YAG lasers should not be rejected. The present work regards the effects of gamma radiation on performance of Er:YAG and CTH:YAG lasers.
Pulse Narrowing in a Nonlinear Directional Coupler Consisting of Two Parallel Semiconductor Optical Amplifiers
Authors: Hsu Chih-Wei , Yang C. C.
Published: February 2023

The pulse break-up phenomenon during nonlinear coupling in directional couplers made of Kerr media, such as optical fiber, can lead to pulse narrowing and has been used for passive mode-locking of Er-doped fiber lasers [1,2]. In this paper, we demonstrate the similar mechanism in directional couplers made of two parallel semiconductor optical amplifiers. In such a directional coupler with an appropriate length, the leading edge of an input pulse can couple into the cross amplifier; however, the high power of the central part saturates the bar amplifier and breaks the phase-matching condition for linear coupling. Because of the long recovering time of gain saturation, the trailing edge of the input pulse is effectively depressed, although it stays in the bar amplifier. Therefore, the pulse is effectively narrowed. By placing such a directional coupler in a ring cavity, we have numerically shown that periodical short pulses evolved from a long pulse inside the cavity under appropriate conditions, similar to the passively mode-locking results using a saturable absorber. To extract laser energy, we used the cross amplifier as the output coupler and found that the peak power (pulse width) of the mode-locked output could be higher (shorter) than the intracavity peak power (pulse width). A detailed investigation showed that the relative strength of the output pulse and the intracavity pulse depended on the length of the directional coupler. Also, we found that mode-locking results could be adjusted by the relative gain of the two amplifiers. There exists quite a large parameter space for the mode-locking phenomenon to occur. This implies that the implementation of such a passively mode-locked semiconductor laser should be feasible.
Compact I2-Stabilized Extended Cavity Diode Lasers
Authors: Simonsen H. R.
Published: February 2023

The iodine-stabilized 633 nm He-Ne laser is widely used as wavelength standard [1]. With the recently available diode lasers in the range 630 to 640 nm new and more compact wavelength standards in the red part of the visible spectrum [2], [3] are attractive. The P(33)6-3 transition is particular interesting because a direct frequency comparison (roughly 1 GHz frequency difference) with the iodine-stabilized 633 nm He-Ne laser is possible.
Temporal and Spectral Characteristics of Phase Conjugation Signal under 4-Wave Mixing in Active Medium of CO Laser
Authors: Afanas'ev L. , Ionin A. , Klimachev Yu. , Kotkov A. , Seleznev L. , Sinitsyn D.
Published: February 2023

The phase conjugation (PC) reflectivity of the laser radiation inside its own laser medium reflects the non-linear properties of the medium. To study the properties of carbon monoxide (CO) laser medium the temporal and spectral characteristics of PC reflectivity of pulsed e-beam controlled discharge cryogenically cooled CO laser radiation under degenerate four-wave mixing (DFWM) inside its own laser medium were studied experimentally. The interaction length of DFWM was about 100 cm. The pulse length of the CO laser beam was 50 - 500 µs, the gas density was up to 0.5 Amagat, the gas temperature was about 120 K.
Simulation of Beam Filamentation in High-Power Semiconductor Amplifiers
Authors: Dai Zheng , Unger Peter
Published: February 2023

The suppression of beam-profile filamentation is a challenging task for semiconductor laser amplifiers. In recent times, diffraction-limited, high-power amplification up to 5 W CW and 21 W under pulsed operation has been achieved [1]. In order to obtain high-power amplification with good beam quality, we have used the beam propagation method (BPM) to simulate the disturbance of the refractive index variation. In this paper, we will discuss different mechanisms of the beam filamentation and methods to avoid it.
Spectro-temporal dynamics of a diode laser in an external cavity Application to Intra-Cavity Laser Absorption Spectroscopy
Authors: Uschanoff N. , Stoeckel F. , Lacot E.
Published: February 2023

Intra Cavity Laser Absorption Spectroscopy (ICLAS) is one of the most sensitive techniques for gas absorption measurements. This technique is based on the high sensitivity of a highly multimode laser to very weak spectrally selective intracavity losses during the start-up of the laser generation. The observed spectrum is equivalent to the one obtained in classical absorption with an equivalent path length given by Leq = c. tg (c is the velocity of the light and tg the time of the observation).
Design Parameters of Convective Cooled High Power Cw CO2 Lasers
Authors: Nath A K , Choudhary P , Biswas A K
Published: February 2023

High power CO2 laser have been designed and developed utilizing many different excitation schemes, electrodes configurations and gas coding schemes. Many papers describe the detail design of the laser systems, still it is not obvious how to determine different parameters of a laser of given out put power i.e. dimensions of discharge volume, gas pressure and mixture, optical resonator configuration etc. More recently, Schuocker [1] has outlined the design considerations of ultra high power CO2 lasers and assessed the feasibility of realizing output power in 100 kW range in co-axial discharge configuration with fast axial gas flow.
Capacitively coupled radio-frequency excited infrared He-Cd laser
Authors: Telbizov P , Petrov T. , Grozeva M. , Sabotinov N. , Mentel J. , Teuner D. , Mizeraczyk J.
Published: February 2023

Recently the transverse capacitively coupled radio frequency (CCRF) discharge was successfully employed for excitation of a considerable number of visible and infrared ionic transitions of different inert gases and metals [1]. One of the most promising as a practical radio frequency excited laser is the He-Cd laser, capable to oscillate simultaneously at many lines through the whole visible spectrum [2].
Long Double Discharge Controlled Nanosecond Electron Beam Generation
Authors: Udrea M. , Pointu A.M. , Modreanu G. , Ganciu M.
Published: February 2023

The generation of intense electron beams by superposing two discharges has been reported, recently /1/, /2/. A new device which delivers a 0.2 - 0.5 m length high intensity electron beam in low pressure (0.1 - 3 mbar) argon discharge tubes is presented. A common K1K2 hollow cathode serves both as a pulsed discharge cathode and a d.c. discharge cathode. A1 and A2 are the main discharge and the d.c. discharge anodes, respectively. A stable electron beam is developing longitudinally, centered inside the tube, only for critical values of the auxiliary discharge current, for a given gas pressure. A 2 mm diameter plasma channel which is produced by the electron beam itself is surrounding the electron beam. A pulsed high voltage supply (60 kV ,100 ns, 500 A) and a continuous 6kV/200 mA power supply are used. The temporal behaviour of the electron beam was determined by means of a Faraday cup and a 500 Mhz Tektronix 540 oscilloscope. Less than 4 ns FWHM beam intensity was found. The power density of the electron beam is estimated to be about 3. 1010 W / cm2.
Gap Scaling of Rf Excited Slab Waveguide Molecular Gas Lasers With a Fixed Excitation Frequency
Authors: Villarreal F , Cameron A A , Colley A D , Baker H J , Hall D R
Published: February 2023

The geometrical scaling for radio frequency excited slab waveguide molecular lasers has been described in recent years by the concept of similarity and similarity scaling laws[1]. This provides a method to relate pressure p, electrode spacing d and excitation frequency f such that we can understand and predict the behaviour of the slab waveguide laser. In practice the lack of power supplies with an adequate range of frequency tunability make it difficult to fulfil the similarity conditions. A necessity has arisen for a more realistic model which describes laser behaviour over a wide electrode separation range where the excitation frequency remains constant.
Similarity in the infra-red laser gain of a sputtered He-Cu mixture excited by radio-frequency and hollow-cathode discharges
Authors: Adamowicz T.M , Mizeraczyk J. , Krupa A. , Konieczka J. , Mentel J. , Teuner D. , Sabotinov N.
Published: February 2023

Sputtered noble gas-metal vapour ion lasers excited by hollow-cathode (HC) discharge have been promising sources of UV radiation for many years [1], however, some technological problems have made them unpractical. The recent investigations of the noble gas-metal vapour ion lasers excited by the transverse capacitively-coupled radio-frequency (RF) discharges disclosed similarities between the HC and RF discharges [2]. This suggests that the RF discharge may be an advantageous substitute for the HCD in the case of the sputtered He(Ne)-metal vapour ion lasers.
Experimental investigations for modelling a 1.3µm waveguide amplifier
Authors: Löftier P. , Sautter H.
Published: February 2023

In commununicat ions technology 1.3µm is an important transfer wavelength because of an absorption and dispersion minimum at 1.3µm of typical optical silicon fibers. In order to realize an all-optical communications system for 1.3µm one essential component is still lacking, the optical amplifier. For integrated optical systems in the future it would be desirable to have 1.3µm waveguide amplifiers. Therefore the three-valent rare earth ion Pr is used as an optical active medium. The Pr3+-level lG4 is activated by a pump laser at 1020nm. A simultaneous signal beam of 1.31µm photons stimulates the Pr3+-transition 1G4→ 3H5 and thus amplifies the intensity of the signal. Competing non-radiative processes are multiphonon-relaxation from 1G4 to 3F4 and cross-relaxation among two Pr-ions (e. g. 1|G4-->3H6 / 3H4-->3F2), respectively energy transfer along several Pr-ions to a quenching center. It is necessary to have a host material with low-energy phonons to suppress the multiphononrelaxation. Chalcogenides with a typical quantum efficiency of more than 40% are more convenient for this than fluorides with a quantum efficiency of about 3-5%1.
Transmission of solitons at 15 GHz and 20 GHz generated by pseudorandom modulation of laser diodes using TDM
Authors: Revuelta J. , Pesquera L. , Mirasso C. R.
Published: February 2023

We have recently shown that pseudorandom sequences of solitons can be generated and transmitted at 5 GHz by direct modulation of laser diodes (LD) when biasing slightly below threshold (C.R. Mirasso and L. Pesquera, IEEE PTL 7. p. 437, 1995). Using this bias current pattern effects are avoided and the fluctuations originated in the LD are reduced. Here we perform numerical simulations to study the transmission of pseudorandom sequences of solitons at 15 GHz and 20 GHz obtained by time division multiplexing (TDM) of 1.55 µm LD modulated at 5GHz and biased slightly below threshold. A narrowband optical filter is used to limit the large bandwidth of the signal produced by the chirping. To reduce soliton interaction the pulses are compressed by using 0.6 km of a normal dispersion fiber (D = −20 ps/nm km). In this way the pulses launched in the fiber have a 10 ps witdh. A large timing jitter is obtained after transmission over transoceanic distances due to the pulse-to-pulse frequency jitter originated in the LD. This jitter is reduced by using guiding filters every 25 km with a bandwidth of 250 GHz. The results in the figure for 15 GHz (left) show that filters are effective to reduce timing jitter. However, in the 20 GHz (right) transmission sequence the interaction leads to errors (see the set ”11” near the end of the sequence). Then more effective soliton control systems (i.e. sliding-frequency filtering) should be used to reduce interaction effects.
Performance Implications of Three-Mirror Fabry-Perot Demultiplexers for Dispersion Supported Transmission of Two and Three 10 Gbit/s Channels Separated 0.5 nm
Authors: Freire Mário M. , de Carvalho Álvaro M. F. , da Silva Henrique J. A.
Published: February 2023

Single-channel optical transmission at 10 Gbit/s up to 253 km of standard singlemode fibre (SMF) has been demonstrated, using the method of dispersion supported transmission (DST) [1]. However, in a recent DST experiment at 20 Gbit/s, the link length was reduced to 53 km SMF [2], as expected from the principle of dispersion supported transmission [1]. One solution for high capacity DST on long spans of SMF is the optical transmission of wavelength division multiplexed (WDM) 10 Gbit/s channels. In [3], we have discussed the impact of single and double cavity Fabry-Perot demultiplexers on the performance of dispersion supported transmission of two WDM 10Gbit/s channels separated 1nm. Nevertheless, to reduce the differences on the system performance due to a different value of fibre dispersion at the wavelength assigned to each channel, narrow channel spacings are required.
Determination of the Microwave Phase Error in Switchable Optical Time Delay Networks for Phased Array Antennas
Authors: Schäffer Christian
Published: February 2023

Switchable optical true time delay (TTD) networks are used for the control of phased array antennas and for microwave signal processing in the optical domain. Photonic networks are used because of their wide instantaneous bandwidth.
Research on the Characteristics of Excimer Laser Raman Amplification and Beam Combination
Authors: Lou Qihong
Published: February 2023

Various research have been done for the Stimulated Raman Scattering in high pressure gas pumped by excimer laser, more wavelength output can be obtained both by Stokes and anti–Stokes shifts. On the other hand, Raman beam clean–up and Raman beam combination are useful for the laser fusion and high intensity laser systems.
Novel Highly Efficient Neodimium-Doped Calcium Gallium Germanium Garnet Laser With Diode Pumping
Authors: Belovolov M.I. , Dianov E.M. , Timoschechkin M.I. , Morosov N.P. , Prokhorov A.M. , Timoschechkin K.M.
Published: February 2023

Although a number of Nd-doped crystals has been grown and studied, Nd3+ -doped lasers have received considerable attention up to now. Laser crystals of Nd3+:Ca3Ga2Ge3O12 -garnet (Nd-CGGG) with Nd3+ concentration of 0.8 at.% were grown and stimulated emission was observed in 1978/1/. But the efficiency of Nd-CGGG crystals for the mordem applications is still not complitly clear.
Efficient Single-Frequency Light Sources with Emission Wavelengths from the Visible to the Infrared Spectral Region
Authors: Freitag I. , Bode M. , Czarske J. , Tünnermann A.
Published: February 2023

For laser-based metrology, efficient sources of stable coherent radiation in the visible and near infrared spectral region are required. While stablity is a common request of most metrology applications, the desired laser wavelength differs with the specific application. Fiber sensors require laser emission at their attenuation minimums at 1.3µm and 1.5µm [1], whereas visible light sources are advantageous when the signal strength increases with the laser frequency, for example in laser-Doppler-velocimetry [2]. A further advantage of visible light is the easy optical alignment. Diode-pumped solid-state lasers are attractive sources for metrology applications because of their high inherent intensity and frequency stability. However, the emission of most solid-state lasers is limited to the near infrared spectral region. We report on stable single-frequency light sources with emission wavelength covering the spectral range from visible to near infrared.
Development of tunable high spectral parity narrowline dye and Ti:Al2O3 lasers using a single self-selection resonance interferometer
Authors: Deneva Margarita A.
Published: February 2023

Simple low background emission (≤ 10−6) wideband tunable (~100 nm) narrowline (~10-20 pm) dye and Ti:Al2O3 lasers are developed. They employ our original selective cavity (Fig.l) in which a single high thickness (~100µm) interferometer (interference wedge - IW or a piezopushing Fabry-Perot - FPI) selects a single narrow line [1]. The laser axes cross the interferometer at two appropriate angles θ1 and θ2 and thus only a single coincidence of resonances can occur for both sequences of resonant orders corresponding to θ1 and θ2 respectively in the region of ~ 100 nm and higher. The tuning of the coinciding resonances can be obtained by the IW translation or by the FPI piezopushing. Along with simplicity and the use of a single interferometer, the configuration in Fig.l presents two natural advantages by which the proposed cavity differs from the traditionally used selective schemes: i) absence of the non-selective reinjection of the emitted light for both outputs of the active medium; ii) for a single round-trip the light crosses the interferometer four times which increases essentially the contrast of the selection. The noted differences are the base for a high spectral purity narrowline emission.
Growth and Investigation of Structure-Nonequivalent Doping Centers in LiCaAlF6:Gd3+ Single Crystals
Authors: Abdulsabirov R.Yu. , Antonova I.I. , Korableva S.L. , Nizamutdinov N.M. , Stepanov V.G.
Published: February 2023

Recently the first all-solid-state tunable UV laser with direct pumping has been reported [1) This laser is based on the allowed 5d-4f interconfigurational transitions of Ce3+ ions in LiCaAlFF6 (LiCAF:Ce) single crystal. Due to the geterovalent activation nature LiCAF:Ce and LiSrAlF6:Ce3+ (LiSAF) [2] laser media appeared to be quite complex subject for spectroscopic investigations with their laser characteristics strongly dependent on the growth conditions as well as on the presence of charge-compensating additions [2, 3]. Therefore investigations of a variety of the rare earth structure-nonequivalent doping centers in a LiCAF/LiSAF single crystals is of great practical importance.
Control of the laser radiation interaction with tissue by a copper laser monitor
Authors: Arakelian S.M. , Orlov V.N. , Prokoshev V.G. , Klimovskii I.I. , Galkin A.F. , Abramov D. , Taranenko M. , Gordienko V.M.
Published: February 2023

The study of interaction of laser radiation with biological objects requires to overcome of the problems determined by using of optical system combined itself the illumination system and the system of visualization. The laser brigtness amplifier of the copper vapour (i.e. a laser monitor) is a good unit for that.
Modification of molecular composition of atherosclerotically damaged aortic wall under influence of a high power XeCl laser
Authors: Mel'chenko S.V. , Mel'chenko E.D. , Gordov E.P. , Shipulin V.M. , Sukhodolo I.V. , Saprykina E.V.
Published: February 2023

Laser installations developed for laser angioplasty are still far from perfection. Even excimer lasers that have been considered to provide precise influence on a small volume directly irradiated by laser beam show a number of side effects that prevent from their wide applications in clinics. However in our opinion, there was rather incorrect approach to the problem than the problem has no solution. It is known, that the longer is duration of laser pulse the easier it can be delivered through the fiber. But the cost of this easiness is reduced laser power affecting the tissue. In this paper, we report that laser power is the main parameter that determines efficiency of laser beam-tissue interaction.