bluuebunny/crossref_metadata_2025 huggingface dataset:
High power single-frequency operation of continuous wave diode-pumped Nd:YAG ring lasers
Authors: Zellmer H. , Freitag I. , Golla D. , Knoke S. , Schöne W. , Tünnermann A. , Welling H.
Published: February 2023

The laser light sources required for the next generatioin of gravitational wave detectors using Michelson type interferometers have turned out to be extremely sophisticated. To achieve the desired sensitivity of at least 10-21, the lasers have to work at high cw power levels in single-frequency operation with excellent frequency stability and extremely low amplitude noise. Beyond that, they should have a high efficiency, so that operational costs are within reasonable limits.
Time and frequency domain spectroscopy of copper (I) doped beta-alumina
Authors: Lane S. H. , McKinnie I. T. , King T. A. , Dunn B.
Published: February 2023

The driving force behind the present work is the development of a new visible, tunable solid-state laser based on copper (I)-doped β-alumina. The characteristic blue/green emission of this material would make it the first tunable inorganic solid-state laser to operate in this region. An important stage in this work is the spectral characterisation of copper (I) in the β-alumina host. We report on time and frequency domain fluorescence measurements as well as spectral measurements of absorption and excitation.
Transient gain/loss in tunable solid-state vacuum ultraviolet laser media
Authors: Cashmore J. S. , Hooker S. M. , Webb C. E.
Published: February 2023

Broad-band vacuum ultraviolet (VUV) fluorescence on the 4fn−1 5d → 4fn transitions has been observed in a number of rare-earth activated fluoride hosts.1 Ultraviolet (UV) laser oscillation on the 5d → 4f transition in Ce has been observed in a number of hosts,2,3 and recently VUV laser oscillation at 172 nm has been reported4 in LaF3:Nd3+ pumped by a pulsed-discharge molecular F2 laser. A simplified energy level diagram illustrating the transitions involved, together with the F2 laser induced VUV fluorescence spectrum5 for a 1% doped sample of LaF3:Nd3+ is shown in Fig. 1. F2 laser pumped rare-earth–doped fluorides, since they operate through linear processes, offer the prospect of a convenient source of intense tunable VUV laser radiation, with applications in photochemistry and photolithography.
Principle of surface cleaning by laser impact
Authors: Boquillon J. P. , Oltra R.
Published: February 2023

CW or pulsed Nd:YAG lasers are among the lasers that have known one of the largest scientific and industrial developments, principally through thermical processes related to the high-average-power of emission. Another mode of operation was rather reserved to the scientific domain: the Q-switched mode leading to very short pulse durations (5 to 30 ns) and very high peak powers of a few tens of MW. This generates optomechanical effects where the thermical exchanges do not have time to appear and to spread, the average power of these lasers being moreover limited to 10 or 25 W.
Optical phase conjugation in the short-time range: Generation of sub-nanosecond laser pulses with Q-switching by stimulated Brillouin scattering (SBS)
Authors: Kramer M. , Brückner V.
Published: February 2023

We studied Q-switch1,2 of a pulsed Nd: YAG laser using the phase-conjugating properties of stimulated Brillouin scattering (SBS) inside the laser cavity. The laser cavity (see Fig. 1) consists of a flashlamp-pumped Nd:YAG rod as the active medium and a conventional two-mirror arrangement (M1, M2) with a SBS-cell containing acetone surrounded by two lenses (L1, L2). Caused by a non-confocal setup of the lenses, one can achieve high geometrical losses (per round trip) of the laser radiation emitted from the Nd:YAG rod. The low feedback between the resonator and the active medium continues as long as the intensity in focal point F inside the SBS-cell is below threshold for SBS. Thus a high inversion population is built up in the Nd:YAG rod during the increase of the flashlamp intensity. At high intensities of the laser wave-phase-conjugated backward scattering starts from F in the liquid switching the resonator quickly from high to low losses (Q-switching). As a result a short laser pulse is generated, which has—caused by the non-confocal setup—a measurable focal point outside the cavity. Depending on the relation between gain of the Nd:YAG rod, SBS reflectivity of the acetone and light intensity we found one, two, or three pulses of 2–3 ns duration with 10 mJ energy each, separated by the round-trip time between outcoupling mirror M2 and SBS scattering point F. These results can be explained qualitatively in the scope of ABCD-matrix theory and Gaussian beam propagation. Numerical calculations of the beam propagation permit to draw conclusions concerning the existence of a focal point and the "prehistory" of the phase-conjugated pulses. Even if starting 0.1 μm apart from the optical axis, a laser beam will exceed the cross section of the Nd:YAG rod (7-mm diameter) in 10 round trips only, which is equivalent to high geometrical losses of the laser wave in the resonator and a short "prehistory." Indeed, the laser pulse appeared 80 μs after the peak of the pump pulse (FWHM 500 μs). By changing the oscillator configuration (resonator length, position, and focal length of lenses), we achieved pulse peaks with 100 ps duration on top of a broader background pulses (signal to background up to 10:1). By using a saturable absorber outside the laser resonator, the background was suppressed and up to 1 mJ pulse energy left. The sub-nanosecond pulses were recorded with a streak camera at the second harmonic (see Fig. 2). These pulses appeared 100 μs before the peak of the flash lamp intensity. As explanations for the highly reduced pulse lengths of the output pulses optical breakdown by generation of a plasma in focal point F, mode-locking by multiple reflection between M2 and F and pulse shortening by oscillation of the reflection point F in the SBS-cell will be discussed.
High efficiency in a double-pass Brillouin amplifier with noise suppression
Authors: Glick Yaakov , Sternklar Shmuel
Published: February 2023

Brillouin two-beam coupling has been used to achieve gains as high as 109.1 For a given input signal power there is a maximum pump extraction efficiency, and therefore an upper limit to the attainable gain for a given pump power.2 For example, for a 0.1 mW input signal the maximum experimental efficiency is about 2%, so that for a pump power of 20 MW the maximum gain is 4 × 109. The cause of this efficiency limitation is the presence of spontaneously scattered noise at the Stokes-shifted frequency. This noise arises from scattering of the pump light by acoustic fluctuations in the medium and will be amplified by the same factor as the input signal. In this work we present a system that can overcome this limitation and achieve higher efficiency and gain.
A differential phase heterodyne microscope using integrated optical modulator
Authors: Baranov D. V. , Zolotov E. M. , Svidzinskyi K. K.
Published: February 2023

Recently interferometric heterodyne microscopes have been developed1–3 that can measure surface profile with high precision (up to 1 Å in depth). But this value of depth resolution is by two orders worse than the theoretical sensitivity of this type of heterodyne microscopes. The main reason this fact is that the conventional scheme of a microscope and its extent are affected by microphonics and mechanical instability in the system. In this paper we have proposed and demonstrated the possibility of replacement of some bulk optical elements (in particular, a Bragg cell) with integrated optical and fiber-optic elements that are exposed to external influence in a smaller degree.
Crystalline waveguide lasers
Authors: Trapper A. C.
Published: February 2023

Summary not available.
Improved laser performance of Tm3+ and Pr3+-doped ZBLAN fibres
Authors: Barber P. R. , Pask H. M. , Mackechnie C. J. , Hanna D. C. , Tropper A. C. , Massicott J. , Davey S. T. , Szebesta D.
Published: February 2023

In this paper we present the performance of TM3+ and Pr3+-doped ZBLAN fibre lasers at blue, green, and red wavelengths, both pumped efficiently with the output of Yb3+-doped silica fibre lasers.1
Photochemical modification of teflon using water to generate adhesive properties
Authors: Murahara Masataka , Toyoda Koich
Published: February 2023

A powerful adhesion of teflon featuring its excellent corrosion resistance and stainless steel was performed by using an epoxy resin-based bonding agent. Adhesion strength was 120 times more than that of untreated teflon, which has virtually no affinity with chemicals and solids.
Nanosecond pulses wavefront correction using photorefractive self-pumped phase conjugate mirror
Authors: Mager L. , Pauliat G. , Garrett M. H. , Rytz D. , Roosen G.
Published: February 2023

Wavefront distortions (as those introduced by a thermal lens) may be compensated using phase conjugation. This is already achieved with a self-pumped phase-conjugate mirror using stimulated Brillouin scattering. But another possibility is to implement a phase conjugate mirror using photorefractive effect. That is the way we have chosen in order to compensate phase aberration introduced on a nanosecond laser beam. We show in this conference that it is indeed allowed.
Effect of sluggish phase-conjugate feedback on laser diode dynamics
Authors: Langley L. N. , Shore K. A. , Agrawal G. P.
Published: February 2023

Phase-conjugate optical feedback has been used recently to achieve linewidth narrowing in external cavity laser diodes as well as for improving the characteristics of laser diode arrays. It is well known that conventional mirror feedback can cause dramatic changes in the dynamical behaviour and noise properties of laser diodes. Of particular importance in such cases is the phase of the light returned to the laser after a round trip of the external cavity. Phase-conjugate mirrors, on the other hand, have the property of reversing the phase of light incident upon them. Consequently there is a zero round-trip phase change in an external cavity formed with a phase-conjugate mirror.
Trace analysis of aromatic hydrocarbons by time-integrated laser-induced fluorescence spectroscopy
Authors: Bublitz J. , Dickenhausen M. , Todt S. , Grätz M. , Schade W.
Published: February 2023

During the last years, laser-induced fluorescence techniques with fiber-optical sensors have been established in remote sensing of various environmental pollutants in different media.1,2 A sensitive analysis of contaminations in a natural surrounding requires an accurate separation between the fluorescence signal from the background media and the pollutant to be detected. Besides only measuring the fluorescence intensities, a time-resolved recording of the fluorescence at particular observation wavelengths improves the sensitivity of the method considerably, when oil or fuel contaminations should be detected.
Characteristics of optical fibers for UV-laser sensor applications
Authors: Karlitschek Peter , Hillrichs Georg
Published: February 2023

Fiber optical sensor applications for the determination of pollutants are often based on molecular fluorescence. Excitation is achieved by UV radiation that has to be transmitted through an optical fiber. Unfortunately, interaction of intense UV radiation with the commonly used fused silica fibers induces additional absorption by formation of colour centers, which is highly undesirable in sensing applications.
All-solid-state diode-pumped cw femtosecond Cr:LiSrAlF6 lasers
Authors: Mellish R. , Hyde S. , Barry N. , French P. M. W. , Taylor J. R. , Delfyett P. J. , Florez L. T.
Published: February 2023

Previously we generated sub-100 fs pulses from a Cr:LiSAF laser using first a dye saturable absorber,2 and then a MQW saturable absorber,3 to initiate KLM and achieve self-starting for only 500-mW-absorbed argon ion pump power. Now 670-nm diode-pumping of a truly continuous wave Cr:LiSAF laser, which tuned from 799 to 860 nm with a minimum threshold of 70 mW, has yielded up to 160 mW of output power with 1.5% output coupling. Full duty-cycle active mode-locking was demonstrated using an acousto-optic modulator which yielded~300 ps pulses.4 An all-solid-state passively mode-locked laser was demonstrated using RPM5 with the MQW absorber of reference.3 Stable, self-starting, c.w. mode-locked pulse trains at 250 MHz were observed which were as short as~60 ps duration, as measured using a sampling streak camera.4 When a standard four prism sequence was incorporated into the cavity, trains of pulses as short as 600 fs were measured using an SHG autocorrelator.
Permanent all-optical poling of octupolar molecules
Authors: Fiorini Céline , Charra Fabrice , Nunzi Jean-Michel , Zyss Joseph
Published: February 2023

Conjugated intramolecular charge transfer systems such as the paranitroaniline derivatives have remained so far one of the most studied classes of organic molecules with enhanced quadratic optical properties. Nevertheless, under the influence of dipole/dipole interactions such molecules are prone to form light scattering aggregates in dilute media or crystallize in centrosymmetric lattices, that results thus in the material having no macroscopic second-order susceptibility. This approach was recently revised, and a new engineering scheme was proposed: octupolar molecules, that can possess large nonlinear optical properties together with good transparency but that do not possess a permanent dipole moment, may circumvent the problem discussed above.1,2 However, since the absence of dipole moment in such molecules prevents dipolar orientation, no polar order can be expected from standard polarization techniques such as Corona poling.
Oscillation on new transitions of CO2 molecules in the 10.4–11.6µm range
Authors: Gorobets V. A. , Petukhov V. O. , Churakov V. V.
Published: February 2023

During investigation of hot band (01111110) oscillation spectrum in the TEACO2 laser,1,2 we have observed several lines in the 875–882 cm-1 range that have not been referred to in this band. These lines have not been identified due to insufficient monochromator resolution used in experiments and the absence of exact spectroscopic data at that time. Nevertheless, it has been supposed2 that these lines belong to a "double hot transition," for example, 10°0-20°0 (04°0) band.
1.48µm pump-diode-driven mode-locked Er fiber laser
Authors: Okhotnikov O. G. , Araújo F. M. , Salcedo J. R.
Published: February 2023

Current modulation of a laser diode (LD) may lead to pulse chirping effects at wavelengths matched to the bandgap wavelength. From this point of view, the intracavity pump LD yields some compromise: the phase modulation may be sufficiently high to mode-lock the fiber laser, however chirping is low at the signal wavelength. This method has recently been demonstated to achieve active modelocking in an Er3+-doped fiber laser with a 980-nm laser diode acting as pump source and phase modulator.1,2 However, pulse duration (≈400 ps) was limited by the low depth of phase modulation since the index change decreases for wavelengths far from the band-gap wavelength. It is expected that the level of phase modulation will be higher with 1.48-p.m MQW LDs because their bandgap wavelength is closer to the operating wavelength of the Er-doped fiber laser.
Er3+ absorption and optical gain in Al2O3 waveguides
Authors: van den Hoven G. N. , Radius E. , Snoeks E. , Polman A. , van Dam C. , van Uffelen J. W. M. , Smit M. K.
Published: February 2023

Planar A12O3 waveguides were fabricated by sputter deposition of A12O3 onto a thermally oxidized silicon (100) substrate. A SiO2 layer was deposited on top of this as a cladding. The nominal layer thickness of 6µm thermal SiO2, 0.60 µm A12O3 and 1.35µm top SiO2 result in singlemode planar waveguide films at 1.5µm. Annealing of these films at 825°C was performed to achieve a low optical loss of 0.35 dB/cm.1 Preceding the deposition of the top cladding, 2 × 1016 Er/ cm2 was implanted into the A12O3 film at 1.35 MeV, with the sample held at 77 K. Using Rutherford backscattering spectrometry, an A12O3 layer thickness of 430 nm and a Gaussian Erbium concentration profile at a depth of 250 nm (full width at half maximum, 135 nm) were measured. The Erbium peak concentration is 1.4 at.%. Upon excitation with an Ar-ion laser the film shows intense room temperature photoluminescence around 1.53 pm due to intra-4/ transitions in Er3+ (Fig. 1, solid line). The luminescence lifetime is 4.5 ms. Earlier work characterizing the photoluminescence properties of similar Er-implanted A12O3 films show that high concentrations of optically active Erbium are attainable without strong concentration quenching effects.2 However, cooperative upconversion was observed in films with an Erbium concentration of 3.6 at.%.
Recent advances in different optics
Authors: Knop K.
Published: February 2023

Summary not available.
Planar holographic elements
Authors: Friesem A. A. , Amitai Y. , Reinhorn S.
Published: February 2023

Planar optical elements combine holographic elements with a substrate mode planar structure where the light is trapped inside the structure by total internal reflections. As a result, usual free space propagation can be replaced by guided propagation in the planar structures on which holographic elements are recorded on either side. These configurations can thus be very compact and readily modularized, so as to eliminate the usually needed, extreme alignment accuracies between input light sources, elements, and output detectors in display, interconnect, and optical data processing applications.
On-line distance and power density measurement in laser milling
Authors: Wisselink F. W. A. , Beckmann L. H. J. F. , Heuvelman C. J. , Meijer J.
Published: February 2023

To control and master the laser milling process it is important to measure the achieved depth and power density online. The measurement method presented in this paper allows to measure depth and power density indirectly by means of a time measurement.
The helicopter-born Obstacle Warning Lidar (OWL) system using an LD pumped Nd:YAG laser
Authors: Saito Hideaki , Doshida Minoru , Mine Yasuharu , Ota Kei , Takada Youichi , Tanaka Toshitsugu , Kubomura Hiroshi , Takahama Yuzuru
Published: February 2023

Over-ground wires occasionally cause serious accidents of helicopters because the pilot could not recognize them so clearly on his flight. However, the conventional imaging system could not provide their image even on a clear day, because of their small contrast to the background.
Differential-absorption-Lidar monitoring of geophysical gas emissions
Authors: Svanberg S.
Published: February 2023

Summary not available.
Lidars for tropospheric and stratospheric ozone
Authors: Swaart D. P. J.
Published: February 2023

Summary not available.
Effect of guided modes on spontaneous emission in planar microcavities
Authors: De Neve H. , Baets R. , Borghs G.
Published: February 2023

The spontaneous emission behaviour of a material is influenced by the presence of a microcavity. Time resolved measurements have clearly demonstrated the enhancement of the lifetime for spontaneous recombination in planar-type microcavities.1 In addition, these devices can also exhibit a more directional light emission and a narrower emission spectrum as compared to conventional LED structures. Upon correctly quantizing the electromagnetic (EM) field in the presence of a cavity, one noticed that the spontaneous emission rate is proportional to the electric field strength of the various EM modes at the position of the active material.2 These models give good agreement with experimental results.3,4 In various cases, however, the model does not completely fit the experimental data. This could be explained by the presence of guided modes in the structures, not taken into account by many models. We have developed a model describing the spontaneous emission behaviour including the effect of the guided modes and the reabsorption of light by the active material within planar microcavity structures.
A high phase-flat fill-factor reflective ferroelectric liquid crystal spatial light modulator for real-time adaptive phase modulation
Authors: Gourlay J. , Vass D. G.
Published: February 2023

Spatial Light Modulators (SLM) performing the function of adaptive phase modulating elements have a wide variety of useful applications such as switchable holographic optical interconnection.1 A very attractive generic type of SLM is the Ferroelectric Liquid Crystal over Very Large Scale Integration (FLC/VLSI) SLM.2 This device has a FLC cell fabricated on top of a custom designed VLSI silicon backplane. The backplane contains an array of pixel memory elements, pixel mirrors, and addressing circuitry. The controllable pixels in the SLM modulate the relative phase by exactly 0 or π due to the switchable uniaxial nature of the FLC structure. Only recently has the full potential of these devices become made available through planarisation techniques. By burying the VLSI circuitry under films of oxides and then mechanically polishing the wafer, as one might polish a mirror, large fill-factor mirrors with a high optical quality have been achieved. Such a high optical quality is crucial if the devices are to be truly useful in high performance optical systems.
Liquid-crystal photonics
Authors: Tabiryan N. V. , Tschudi T. , Vogeler T.
Published: February 2023

Orientation of liquid crystals under the action of the electric field of a laser beam has many things in common with the orientation phenomena induced by a low-frequency voltage. The latter has found presently many applications in electro-optics providing new display principles while several fundamental features of laser-induced orientational phenomena still has to be studied.
Silicon backplane VLSI-liquid crystal smart SLMs: Recent technical advances and potential applications
Authors: de Bougrenet de la Tocnaye J. L.
Published: February 2023

In this presentation we review work in liquid crystal on silicon smart spatial light modulators for optical information processing and switching system applications. Due to the very attractive characteristics of these materials such as high switching speed, low voltage, low power operations, high optical quality and contrast, the paper will focus on the integration of ferroelectric liquid crystals (FLC) and silicon-chip technology. This consideration is illustrated by the recent gain of attention paid to these devices in the literature.
Integrated silicon adaptive mirror
Authors: Vdovin Gleb
Published: February 2023

Objective of this work is the development of electrostatically controlled adaptive mirror, which is integrated into silicon chip. Integrated mirror combines the advantages of micro-machined device—low cost, tolerance for mass production, and IC compatibility1-4 with geometrical quality, attributed to traditional optics. Applications as a stand-alone adaptive optical element5,6 as well as adaptive component of integrated optoelectronical device3 may be regarded. Technology of fabrication permits integration of electrostatic actuators together with control electronics, which simplifies the structure of adapative optical system.
An optical correlation receiver employing phase modulated optical orthogonal codes
Authors: Strachan Gordon R. , Chaudhuri S. K.
Published: February 2023

A traditional optical to electrical receiver consists of a simple PIN diode followed by a number of electrical signal processing elements, which are required to detect and decode the incoming optical signal. The speed of the data on the optical fiber is limited by the bandwidth of these electrical signal processing devices, which is typically only a small fraction of the available bandwidth on the optical fiber. With the recent advent of practical optical amplifiers it is now feasible to implement a number of the important receiver functions in the optical domain prior to detection by the PIN diode without a loss in receiver sensitivity. By implementing these functions optically we can simplify the electrical section of the receiver and thus increase its bandwidth and yield significant gains in the transmission rate.
Time-domain analysis of pulse distortion in a holographic reflection grating
Authors: Baryshevsky V. G. , Maksimenko S. A.
Published: February 2023

The chirped light pulse dispersion under diffraction by a volume transmission grating has recently been considered in Ref. 1. In the given paper we analyze the problem of a chirped pulse scattering by reflection gratings when the pulse spectral width compares with the grating passband. By analogy with Ref. 1 one can suppose that this spectral region is the most attractive for observation of dispersion effect on pulse temporal profiles. Under these circumstances, both phase and magnitude of grating spectral functions are strongly varied over incident pulse spectrum and, consequently, the conventional approach considering the variation of the phase term, proves to be suitable only for qualitative estimations. Thus, a rigorous procedure of time domain analysis should be applied.
An analysis of the linearly polarised modes in elliptical-core fiber
Authors: Hu Xia , South Richard B. , Rutter Malcolm J.
Published: February 2023

It is well-known that linearly polarised (LP) modes in optical fiber are due to the superposition of true HE or EH modes and that each LP mode has several degenerate modes. Although LP modes are not the exact modes of step-index fiber, they are useful in understanding and analysing field structures and transmission characteristics. There is currently a lot of interest in making optical components such as optical switches, modal couplers, and frequency shifters, etc., using the special properties of few-mode fiber.' Unfortunately, most investigations are obstructed by the mode degeneracy and instability of the lobe orientations in circular-core fiber. Elliptical-core (e-core) fiber can overcome this problem because of its stable mode intensity distribution. As e-core fiber finds more and more applications in optical communication systems and optical fiber sensors,2,3 there is an increasing need for a better understanding of the modal fields and their propagation. Although many papers have contributed to the understanding of light propagation in circular fiber, only a few approximate approaches have been used to study the two lowest-order modes (LP01 mode and LP11 even mode) in e-core fiber.4,5 In this paper, we make a more rigorous analysis of LP modes and their propagation characteristics in e-core fiber.
Multi-channel "Zodiac" excitation and optical extraction geometry for compact, inexpensive multi-kilowatt industrial lasers
Authors: Seguin H. J. J.
Published: February 2023

Design, construction, and operational characteristics of an alternative type of high-power industrial laser is presented. The approach features a multiplicity of diffusion-cooled gain channels, arranged in a radial geometry similar to the Zodiac astrological symbol. Extended area CO2 active media, contained within a plurality of wide but narrow-gap metallic electrodes, is uniformly pumped by a multi-channel, magnetic-loop-coupled, resonant cavity RF system built integrally with the laser body.
Polarization mode dispersion free fiber optic isolators
Authors: Pan J. J. , Xu J. Y. , Shih M. , Cao S.
Published: February 2023

Polarization mode dispersion (PMD), which is characterized by a differential group delay between a pair of principle states of polarization due to the intrinsic and external induced bifringence in fiber optic devices, can limit the maximum transmission bit rate in digital systems and maximum channel capacity in Analog Modulated (AM) system. So far, many PMD measurements of long haul fiber links have been reported. However, detailed PMD characterization in optical components used in fiber optic link, in particular, fiber optic isolator, is limited.1 In this paper, a systematic study of PMD in E-TEK's polarization insensitive fiber inline isolators (PIFI) is reported for the first time. For given device geometry, we found the PMD in these isolators are highly repeatable and can be predicted with high accuracy. Furthermore, several PMD compensated methods can be utilized to fabricate "PMD free" isolator.
Quality-controlled machining of carbon composite materials with an excimer laser
Authors: Hodgson E. M. , Boardman A. D. , Whitehead C. , Cresswell B.
Published: February 2023

Carbon composite materials are of increasing interest in many high-technology applications, but their inhomogeneous nature can cause problems in machining processes, because the mechanical properties are not isotropic. An investigation has been carried out into the details of the mechanisms involved in cutting carbon-fibre reinforced resins with ultraviolet laser light. Excimer lasers offer a way of machining shapes of arbitrary complexity to very fine tolerances, with little impact on the surrounding material. The range of parameters over which optimum machining is obtained has been investigated by several groups, and it has been shown that fairly exacting operating conditions must be met to get a good product.
Parallel machining using high power copper vapour lasers
Authors: Dickinson G. J. , Keith C. A. , Maddocks I. , Richardson M. B.
Published: February 2023

During recent years, interest has developed in the use of copper vapour laser light for precision machining applications. Urenco (Capenhurst) Ltd. has a major laser facility based on four chains of copper vapour lasers each capable of generating peak pulse powers of the order of 0.5 MW. This facility has been used to investigate the effect of beam characteristics on the quality of machining to develop a procedure for optimising parallel machining operations within the CLAMP program (EU 849). Figure 1 shows a schematic of the machining workstation.
Optical code-division multiple-access coding architecture with 2n prime-sequence codes
Authors: Kwong Wing C. , Zhang Jian-Guo , Yang Guu-Chang
Published: February 2023

Recent study1 shows that the performance of an optical code-division multipleaccess (CDMA) network cannot be evaluated by only considering the correlation properties of the selected optical pseudo-orthogonal codes.2,3 The coding architecture (i.e., the structures of the optical encoders and decoders) is another important factor to consider, since it affects the power budget and feasibility of the system. As a result, "tunable prime" and "modified 2
n
" coding architectures, respectively, for the prime-sequence and 2
n
codes have been proposed to improve the power-efficiency.1,4 Recently, "2
n
primesequence" codes, a collection of symmetric binary sequences with weight 2
n
, have been introduced and pose the pseudo-orthogonal and algebraic properties of the original prime-sequence codes.5 To effectively utilize these codes, a novel coding architecture, which consists of a "modified" tunable prime encoder and a 2
n
decoder, is proposed to substantially reduce the power loss, cost, and complexity of the systems using optical CDMA.
An optical fibre yeast concentration sensor based on inter-fibre distributed coupling
Authors: Zhang F. H. , Scully P. J. , Lewis E.
Published: February 2023

A novel fibre optic sensor has been developed, which is capable of accurately measuring yeast concentrations in suspension over a range of 0 to 16 g/1. To date a solution for on-line measurement of suspended particulate masses such as yeast has proved difficult and expensive for many industrial users. The sensor reported in this paper relies upon light being radiated through the cladding of one fibre and detected at the end of an adjacent receiving fibre (Fig. 1). Some light is coupled with no yeast present, but the received intensity grows as yeast concentration increases and more light is scattered into the receiving fibre (Fig. 1). The process of scattering is well understood for controlled laboratory conditions where small spherical particles of predetermined diameters have been employed.1,2
A distributed optical fiber sensing system using elliptical core fiber
Authors: Hu Xia , South Richard B. , Rutter Malcolm J.
Published: February 2023

The novel technology of distributed optical fiber sensor (DOFS) is very attractive because it can measure the spatial distribution and temporal variation of a mea- surand field along the fiber simultaneously.1 Many arrangements of a DOFS system are based on the principle of Optical Time-Domain Reflectometry or Polarisation Optical Time-Domain Reflectometry. However, these backscatter DOFS systems have a main disadvantage: very low signal, which leads to a low sensitivity and low spatial resolution. A so-called forwardscatter method can avoid this problem and is being investigated with great interest.2,3 It is based on the nonlinear interaction between the two counterpropagating pump pulse light and probe light, and for some mechanism the emerging signal is dependent on the external measurand. There are several systems making use of the nonlinear effect between the high intensity pump pulse and the two linearly orthogonal-polarised eigenmodes of probe light in single-mode high birefringence fiber,4,5 which have complicated system structures. In this paper we present a DOFS system making use of forwardscatter method in elliptical-core two-mode fiber. The optical components and signal detection are relatively simple.
Automatic surface defects detection on silicon wafers
Authors: Miron N. , Sporea D. G.
Published: February 2023

The detection of surface defects on silicon wafers is done by measuring the total integral scattered flux, when a sharply focused laser beam (<0.1 mm diameter) normal to the wafer surface is used for inspection.
Nematic liquid crystal director reorientation by regular convective motion due to the acoustic wave
Authors: Akopyan R. S. , Chilingarian Yu. S.
Published: February 2023

The possibility of the forced generation of regular hydrodynamic convective motions in a nematic liquid crystal with homeotropic boundary conditions and under the action of the radiation pressure of an acoustic wave with a periodic transverse intensity distribution are investigated theoretically. The excitation mechanism is as follows. Two interfering acoustic waves are partially absorbed by the liquid crystal. The absorption of an acoustic wave with a spatially periodic intensity distribution produced the same transverse distribution of the radiation pressure acting on the nematic particles. These forces generate steady convective motions of the liquid, whose velocity gradients cause the nematic molecules to rotate. If acoustic waves are absent and the nematic is placed between crossed polarizers, it is opaque to a light wave in normal incidence on the layer. The reorientation of the nematic director creates ordinary and extraordinary light waves, so that the field of view is cleared periodically in space.
Mach-Zehnder switch employing an ultracompact directional coupler
Authors: Janz C. F. , Keyworth B. P. , Allegretto W. , MacDonald R. I. , Fallahi M. , Hillier G. , Rolland C.
Published: February 2023

Directional couplers are important components of integrated optoelectronic devices such as power splitters and combiners, switches, and polarization and wavelength (de)multiplexers. Some recent work on multimode waveguide couplers using widely-spaced access waveguides has demonstrated good performance;1 however, the use of wide couplers carriers the penalty of increased device length. This problem is particularly grievous in deeply-etched, strongly- confining rib waveguides, which are otherwise well-suited to small-dimension devices since small-radius waveguide bends can be employed.2
Effects of asymmetric Fabry-Perot cavity on the switching characteristics of symmetric self-electrooptic effect devices with extremely shallow quantum wells
Authors: Choi Y. W. , Kwon O. K. , Kim K. J. , Lee E. H.
Published: February 2023

Asymmetric Fabry-Perot (AFP) structure in p-i-n diode optical modulator has been the subject of recent research since AFP not only enhances the modulation and contrast ratio but also reduces the operating voltage due to its thin intrinsic region thickness (ti).1,2 When AFP is associated with extremely shallow quantum wells (ESQW)3 in optical bistable symmetric self-electrooptic effect devices (S- SEED), it leads to significantly improved performances, such as lower operating voltage and larger optical bistability even without applied voltage.4 Furthermore, low incident energy for switching would be realized in AFP. Here, we present the quantitative results on the required incident switching energy (Eo) and the switching speed limit of AFP ESQW S- SEED (AE-SEED) using a scattering matrix method and analytically obtained impulse response functions, respectivley.
Thermal and absorption saturation effects on the reading beam intensity limit of an extremely shallow quantum well self electro-optic effect device with asymmetric Fabry-Perot etalon structure
Authors: Kwon O. K. , Choi Y. W. , Kim K. , Lee E.-H.
Published: February 2023

To achieve low operating voltage, fast switching time, and high ON/OFF contrast ratio, we learned that an extremely shallow multiple quantum well (ESQW) symmetric self electro-optic effect device (S-SEED) having an asymmetric Fabry-Perot (AFP) etalon structure, that we named AFP-ESQW S-SEED (AE-SEED), is effective as reported previously.1 In this paper we report experimental results and the analysis of the upper limit of the reading beam intensity.
Tunable single frequency operation of an erbium-doped fibre laser incorporating a novel continuous fibre filter
Authors: Gloag A. , McCallion K. , Johnstone W. , Langford N.
Published: February 2023

Tunable single frequency Er-doped fibre lasers have applications in telecommunications, remote sensing, and high resolution spectroscopy. Several different approaches have been taken to achieve this goal using fibre Fabry-Pérot étalons1 or intracore Bragg reflectors.2 With fibre Bragg gratings, for example, tunability is achieved by physically altering the grating periodicity.2
Active subjects in optical computing
Authors: Chavel Pierre
Published: February 2023

The situation of optical computing has changed dramatically over the last few years because of the development and availability of at least three complementary technologies that now open the way to applications to the parallel processing of a large amount of information.
A compact-high efficiency-flashlamp pumped Ti:Al2O3 laser
Authors: Collier F.
Published: February 2023

Pumping a Ti:Al2O3 laser with another laser, such as a frequency-doubled Nd:YAG laser, limits both the energy of each pulse and the overall efficiency of the system. Pumping Ti:Al2O3 by flashlamps is difficult, however, because of the Ti3+ short radiative lifetime (3.2 μs). Also, we develope an all solid-state power supply that can deliver a 5 kA peak current to the flashlamp on the same time scale. The supply provides a 150 to 300 mA direct simmer current and 10 A pseudo-simmer current (risetime of 100 μs) to allow for spatial centering of the arc in the flashlamp bore. At the top of the pseudo-simmer pulse, the main electrical pulse is provided by an original circuit based on magnetic compression. A maximum energy of 110 J can be delivered to the two flashlamps (55 J per lamp) within 4.5 μs with 75% electrical efficiency.
1.55-μm room temperature laser action of Cr4+:Y3Al5O12 and Cr4+:Y3Sc0.9Al4.1O12
Authors: Kück S. , Petermann K. , Huber G.
Published: February 2023

Tunable solid-state lasers based on transition metal ions have a wide range of applications in the field of ranging, remote sensing, medicine, optical communication, and scientific research. Especially the spectral region around 1.55 μm is interesting, because of the second window of the transmission of fibres for optical communication. In this paper laser action at 1.55 μm of Cr4+:Y3Al5O12 and Cr4+:Y3Sc0.9Al4.1O12 crystals is presented.
Novel techniques for distributed optical-fibre sensing
Authors: Rogers A. J.
Published: February 2023

Distributed Optical-Fibre Sensing (DOFS) provides the means by which the spatial and temporal behaviour of a range of physical fields may be determined. A variety of methods for implementing DOFS have been explored, each, as always is the case, with its own set of advantages and disadvantages.1,2
Origin and application of lateral piezoelectric fields
Authors: Ilg M. , Ploog K. H.
Published: February 2023

A strong piezoelectric polarization exists in strained III-V heterostructures with non-(100) orientation.1 This polarization normally splits up in a component parallel and a component perpendicular to the interfaces. In ideal quantum wells without any lateral structuring only the polarization component perpendicular to the interfaces creates polarization charges and hence electric fields. Research activities up to now have focussed exclusively on these vertical electric fields. The inactivity of the polarization component parallel to the interfaces, however, can be lifted by a lateral patterning of the quantum well. Then the parallel component also generates piezoelectric charges and thus introduces lateral piezoelectric fields. These lateral fields can be significantly stronger than vertical fields. The separation of negative and positive charges can thus be much larger than in the case of vertical fields. Furthermore, lateral fields can be created by much smaller total amounts of piezoelectric charge than vertical fields.
Spatio-temporal population density measurements in a barium vapour laser operated in burst mode
Authors: Mildren Richard P. , Brown Daniel J. , Carman Robert J. , Piper James A.
Published: February 2023

Barium vapour lasers (BVLs) are an efficient (~0.5%), high average power (10-15 W) and high pulse rate (~10 kHz) source operating on a variety of near and mid IR wavelengths (1.13, 1.50, 2.55, and 4.72 microns), with applications including scanning ranging, remote gas detection, and optical fibre testing. The BVL is also an amenable system for studying kinetics of metal vapour lasers, as the atom and ion ground states have visible upward transitions suitable for hook spectroscopy. To date, there has been relatively little work on ground state kinetic issues and the factors influencing prepulse ground state density in metal vapour laser (MVL) systems in general are not fully understood. Previous reports1,2,3 indicate that the observed prepulse metal atom density across the tube bore is well below that expected from thermal considerations. We have studied the factors influencing the pre-pulse ground state density for a BVL operating with both helium and neon buffer gases.
Waveguide gas lasers—recent developments
Authors: Udalov Yu. B. , Peters P. J. M. , Wittemann W. J. , Ochkin V. N.
Published: February 2023

Recent results in the studies of the physics and technology of waveguide gas laser are presented. The main attention is paid to the infrared atomic and molecular gas lasers with electrical discharge excitation, particularly CO and Ar:Xe, although a brief discussion of other types of gas lasers also will be given. Problems concerning a further improvement of the CO2 waveguide laser performance are discussed.
Nd:GdVO4-laser pumped by 1 W laser diode
Authors: Klimov I. V. , Mikhailov V. A. , Shcherbakov I. A. , Zagumenniy A. I. , Boiler K. -J. , Bartschke J. , Knappe R. , Wallenstein R.
Published: February 2023

Recently Nd:GdVO4-crystal was reported to be very promising for high efficiency diode pumped solid state laser.1 In this paper the possibility of high power TEM00 lasing and intracavity doubling is studied for Nd:GdVO4 laser longitudinally pumped by 1-W CW laser-diode array.
Formed-ferrite plasma source for optical pumping the XeF (C→A) laser
Authors: Mit'ko S. V. , van Goor F. A. , van der Holst A. R. , Witteman W. J. , Ochkin V. N.
Published: February 2023

The most important problem encountered in the design of the blue-green optically pumped XeF (C→A) laser is the development of a reliable light source with maximum energy emission at wavelengths between 150 and 160 nm, a geometrical length of ~1 m, and permitting operation in pulse-repetitive mode. A linear formed ferrite plasma source fulfilling these requirements has been developed and tested. To excite the high-brightness light source we used an 800-mm-long ferrite rod, assembled from 1.7 × 4 × 140-mm-long ferrite strips placed end to end, to guide the high-current surface discharge. The ferrite rod was placed near the wall of the 50-mm diameter laser tube, which was made of teflon. The conductive path on the surface of each ferrite strip was prepared by a method, described in Ref. 1. To prevent broadening of the conductive filament due to the discharge plasma, we embedded the ferrite strips in alumina.
Reflection-grating phase-conjugate mirror free of input conditions and compensation for air turbulence
Authors: Honda Tokuyuki , Matsumoto Hirokazu
Published: February 2023

The response time of the photorefractive phase-conjugate mirror can be improved by focusing the input beams and thus increasing the light intensity. A self-pumped phase-conjugate mirror in a reflection-grating ring geometry was shown to be suitable for focused input beams.1 The rise time of several milliseconds was observed with a 100-mW input probe beam. When the beams are sharply focused, however, the phase-conjugate wave may become sensitive to the changes in the angle and the position of the input probe beam. The probe beam and the feedback beam must overlap in a sufficiently long region for the generation of the phase-conjugate wave.
Oxygen ion implanted channel optical waveguides in gallium arsenide
Authors: Choi K. S. , Han D. J. , Chan K. T. , Li G. H.
Published: February 2023

Oxygen ion implantation into GaAs has been studied recently for the purpose of fabricating integrated optical waveguides in GaAs.1,2 It is reported for the first time that as-implanted GaAs exhibits an increase in refractive index of 0.1 to 0.2,1 which implies that the implanted layer can be utilized as the guiding layer for GaAs based waveguides. This paper demonstrates the realization of such an idea by the formation of planar channel waveguides using the novel technique of oxygen ion implantation.
Strong photo-induced refractive index changes in RF-sputtered tantalum oxide planar waveguides
Authors: Roe M. P. , Hempstead M. , Archambault J.-L. , Russell P. St. J. , Dong L.
Published: February 2023

Optical waveguide gratings have a multitude of uses in laser, communications, and sensing systems, in both planar and fibre configurations. They may be fabricated holographically in materials that display high levels of photosensitivity when exposed to UV light. An example is Bragg grating formation in germano-silicate optical glass fibres1 and planar waveguides of similar composition.2 We report here, for the first time, strong UV-induced refractive index changes in sputtered tantalum oxide planar waveguides.
High accuracy sensor for dynamic measurements based on holographic optical elements, semiconductor lasers and detectors
Authors: Hanson Steen G. , Lindvold Lars R.
Published: February 2023

Diffractive optical elements have been of interest as far back as in 1872 where Lord Rayleigh described the fabrication of zone plates by contact copying ruled gratings onto various photorecording materials obtaining higher diffraction efficiency than that of the original. The introduction of the laser brought about a means for recording high pitched gratings as holograms. Recording materials with specific characteristics became important for rendering high diffraction efficiencies, ease of processing, good reproducibility, and high sensitivity and resolution. Combining this with low-cost lasers, detectors, and detector arrays provides new possibilities for optical sensors.