bluuebunny/crossref_metadata_2025 huggingface dataset:
Transverse Mode Selection with Phase Elements
Authors: Oron R. , Danziger Y. , Davidson N. , Friesem A. A. , Hasman E.
Published: February 2023

In a laser resonator operating with many transverse modes, the divergence of the emerging beam is relatively high, resulting in a high M2 value. To reduce the divergence, it is best to reduce the number of the modes, preferably to a single mode. Typically, this is achieved by introducing an aperture inside the cavity, so the laser resonator will operate with a single
TEM
00 mode. Unfortunately, this results in a significant reduction of the output power, since only a small volume of the gain medium is exploited.
Controlled Reduction of Fe-doped KNbO3 by Proton-irradiation
Authors: Brülisauer Simon , Fluck Daniel , Günter Peter , Beckers Lutz , Buchal Christoph
Published: February 2023

We report for the first time on proton-irradiation as a method to precisely adjust the reduction ratio, i.e. the ratio R = [Fe2+]/[Fe3+], of Fe:KNbO3 over three orders of magnitude. By applying this technique, we were able to alter the photorefractive gain Γ from 2.5 cm−1 up to 34 cm−1, the absorption constant α from 0.06 cm−1 up to 2.1 cm−1 and the grating buildup time τ from 1.6 ms down to 34 µs at an intensity I = 200 W/cm2 in a 1000 ppm Fe-doped KNbO3 crystal, for example [1]. The major advantage of ion-irradiation is that it is a very homogeneous and a very reproducible process, which can be applied in subsequent steps on the same sample, to increase the reduction ratio continuously from R = 0.01 up to R = 40, by simply implanting protons of the appropriate dose. Figure 1 shows the change of the photorefractive gain Γ and the absorption constant α as a function of the increasing reduction ratio R for a 10'000 ppm Fe-doped KNbO3 crystal. Further experimental results and a refined theoretical model for strongly reduced KNbO3, together with a set of the basic material parameters for these crystals, which completely explains all the measurements, will be presented at the Conference. Finally it is worth to mention, that this method is quite universally applicable to many other photorefractive crystals, such as BaTiO3 and SBN, and dopants, such as Rh and Mn.
Optical parametric oscillation beyond 6.3µm in periodically-poled lithium niobate
Authors: Lefort L. , Puech K. , Svirko Y. P. , Ross G. W. , Smith P. G. R. , Hanna D. C.
Published: February 2023

Efficient sources of tunable coherent radiation in the near and mid-IR are necessary for many applications including spectroscopy, communications etc. In this contribution we report on the generation of tunable IR radiation obtained from a periodically poled lithium niobate (PPLN) based optical parametric oscillator (OPO).
WDM soliton transmission in dispersion-managed links
Authors: Georges Thierry , Favre François
Published: February 2023

The transmission of 20 Gbit/s path-averaged solitons with in-line control is possible over unlimited distances [1]. In such experiments, Kerr nonlinearity is not a limitation but is used to separate the signal from the noise. Unfortunately, this transmission technique does not allow the increase of the bit rate of a single channel to much more than 40 Gbit/s nor the increase of the overall bit rate with help of Wavelength Division Multiplexing (WDM) because of the Four Wave Mixing (FWM) [2]. The other drawback is the incompatibility to the Non Dispersion Shifted Fibre (NDSF) or standard fibre in the terrestrial networks.
Upgrading standard-fiber soliton WDM systems at 1550 nm to ultra high capacity by appropriate power and dispersion management
Authors: Schürch M. , Hodel W. , Weber H.P.
Published: February 2023

The advent of the Er3+-doped fiber amplifier for optical amplification in the 1550 nm window has revolutionized optical telecommunications. One must, however, keep in mind that most of the existing networks are based on standard fibers (SF) which are not well suited for operation at 1550 nm due to their large group velocity dispersion (GVD) at that wavelength. Upgrading existing networks to higher capacity at 1550 nm has therefore become a major challenge for researchers. A very promising approach in this respect is the use of wavelength division multiplexing (WDM) in combination with dispersion management techniques which allow to compensate the large GVD of the SF at 1550 nm (D=16 ps/(km nm)).
Interactive Fiber Lasers with Low Noise And Controlled Output Power
Authors: Pan J. J. , Shi Y.
Published: February 2023

Summary: DWDM networks with a channel spacing of 0.8 nm or less impose stringent requirements on laser sources of accurate λ and output power control, high λ stability and low noise. However, DFB fiber lasers [1] suffer from low output power for a limited laser length. Using an EDFA to boost the output power increases the noise figure at least a 3-dB. Fiber DBR laser has a high noise due to the relaxation oscillation. In this paper, an interactive fiber laser (IFL) is analyzed and experimentally demonstrated. It is a combination of fiber DFB laser and a fiber DBR laser to have a higher output power and low noise.
High Speed Performance of Mach-Zehnder All-Optical Regenerators using Semiconductor Optical Amplifiers
Authors: Annetts P.J. , White I.H. , Penty R.V.
Published: February 2023

Recent increases in demand for transmission capacity and advances in technology have led to increasingly high information rates in fibre systems. As optical systems have migrated to these higher bit-rates, OTDM and WDM systems have been implemented, with EDFAs providing optical amplification. This has led to the need for all-optical regeneration at very high bit-rates (> 10 Gb/s). Interferometric Optical Wavelength Converters (IOWCs) provide wavelength conversion functionality at high bit rates [1], and give low chirp and enhanced extinction ratio compared with Cross-Gain wavelength converters. The non-linear transfer characteristics of IOWCs have recently led to interest in them being used as regenerators. In this application an IOWC’s noise performance and its potential for cascading is most important and this paper therefore reports detailed theoretical treatment of these parameters using numerical simulation[2].
Wavelength shifting and amplification of optical pulses through cascaded second order processes in periodically-poled lithium niobate
Authors: Banfi G.P. , Datta P.K. , Degiorgio V. , Fortusini D.
Published: February 2023

We report on wavelength-shifting based on cascaded second-order nonlinearities1 in periodically-poled lithium niobate. Wavelength shifting from a signal s at λs=λp+Δ to a frequency-shifted signal f at λf=λp−Δ is obtained under the action of a pump p at λp: the effect is realized through the generation of the second harmonic (sh) of p and subsequent parametric amplification of s driven by sh. In the latter process f is also generated. Exploiting the advantages of quasi-phase-matching, efficient shifting is achieved at pump intensities about two orders of magnitude lower than in traditional second-order materials such as BBO.2
Compact cw laser source for high-resolution spectroscopy between 6.8 and 12.5 μm
Authors: Petrov V. , Rempel C. , Stolberg K.-P. , Schade W.
Published: February 2023

Tunable monochromatic laser sources in the mid-infrared (MIR) spectral range are particularly important for high-sensitivity and high-resolution molecular spectroscopy. The optimum combination of frequency stability and spectral resolution can be provided only by cw laser radiation. Recently considerable progress has been achieved in developing such devices emitting above 3 μm that are based on difference-frequency generation (DFG) in AgGaS2, but the tunability of previously demonstrated all-solid-state DFG schemes was limited to a narrow region near 5 μm because of the requirement of 90° phase matching [1]. We report here substantial improvement of the tunability range using for the first time to our knowledge critical phase matching in AgGaS2 in the cw regime. The freedom with respect to the spectral position of the two pumping laser diodes allows the choice of relatively powerful pumping diodes which compensates for the reduced interaction length. This, in combination with type-II phase-matching, provides maximum output powers on the μW level and tunability between 6.8 and 12.5 μm with a single crystal as short as 1 cm.
Airborne Laser Surveying - Systems and Applications
Authors: Axelsson Rune
Published: February 2023

Airborne Laser Surveying - Systems and Applications. The capability to position accurately geographic data in the horizontal plane has increased enormously by the access to satellite positioning systems (GPS). GPS combined with technology of Laser Range Finding, LRF respectively Laserbathymetri, LBS form versatile tools for accurate survey. Systems for the two applications are presented.
Studies on laser range-gated imaging
Authors: Steinvall Ove , Bolander Göran
Published: February 2023

Gated viewing refers to the principle of time controlling a camera with respect to a pulsed illuminating source. This technique was studied for night photography in reconnaissance applications before the thermal IR techniques were widely adopted. In the early days pulsed xenon lamps were used and they were then replaced by lasers. Today there seem to be a somewhat renewed interest for gated viewing both for underwater and atmospheric applications. This is due to the development on both the laser and the camera side. Powerful diode pumped lasers and camera tubes with higher spatial and time resolution will make this technique and interesting complement to passive EO-imaging.
Recent Advances in Optical Techniques for Fluid Mechanics
Authors: Tropea C
Published: February 2023

Present development in the field of Laser-Doppler anemometry (LDA) is driven on the one hand by the appearance of new components, including more compact and powerful laser sources, integrated optics and more flexible signal data processing capabilities. These efforts show a trend to smaller and more robust instruments, also with a potential cost reduction.
Fast diagnostics of ignition processes by excimer laser induced fluorescence of formaldehyde
Authors: Grebner D. , Müller D. , Triebel W.
Published: February 2023

Laser induced fluorescence (LIF) has been widely used for nonintrusive diagnostics of combustion processes in engines, furnaces and turbines [1]. The best way to reduce pollutant production in such devices is to avoid high temperature peaks during combustion and to develop lean premixed combustion devices without spontaneous ignition. The LIF of intermediates as formaldehyde can be used to study ignition processes. Especially the hot spot formation leading to knocking combustion was analyzed [2]. This measurements were performed using dye laser systems, but the handling of these systems in technical environments is difficult. In contrast powerful UV excimer lasers are mostly applied in the diagnostics of technical systems. Two dimensional concentration fields of various combustion species as OH, O2 or NO could be registered [1].
On-Line Temperature Field Measuring System for Quality Control During Laser Beam Cutting
Authors: Haferkamp H. , von Alvensleben F. , von Busse A. , Thürk O.
Published: February 2023

Compared to other technologically relevant laser machining processes, up to now. laser cutting is the application most frequently used. With respect to the large amount of different materials that can be machined, this technology has reached a stable position within the world market of material processing. Machining quality for laser beam cutting is influenced by various laser and processing parameters. Process-integrated quality techniques have to be applied to ensure high-quality products and a cost effective use of the laser manufacturing plant.
Interband Photorefraction for High Resolution Incoherent to Coherent Optical Converters
Authors: Bernasconi Pietro , Montemezzani Germano , Günter Peter
Published: February 2023

Unlike for the conventional photorefractive effects, in interband photorefraction the photocarriers are excited by with photons whose energy exceeds the material energy bandgap. Because of the higher absorption (α ≈ 103 cm-1), the charge photoexcitation process is much more efficient and gives the possibility to generate a space-charge electric field by modulating the density of the free charges which are not trapped into midgap energy levels. The advantages are faster response times combined with a higher sensitivity. Time resolved four wave-mixing experiments in pure KNbO3 crystals have shown that even at low intensities of few mW/cm2, response times in the μs range can be achieved with a consequent holographic sensitivity of the order of few cm2/J [1].
Temperature and Wavelength Insensitive Miniature Diode-End-Pumped Nd:YAG Laser
Authors: Winik Michael , Lebiush Eyal , Lavi Raphael , Jacket Steven
Published: February 2023

The wavelength of laser diodes change with an approximate rate of 0.25 nm/ °C, mainly due to the change in band gap with temperature. The wavelength change causes absorption length variation of the diode light in the laser crystal. This in turn induces output energy variation with temperature and demands diode temperature stabilization. In diode-pumped Nd:YAG systems this requirement(1) is below ± 4 °C.
Optical Imaging in Medicine
Authors: Delpy D. T.
Published: February 2023

Optical spectroscopy is a routinely used clinical laboratory technique, and since the 1930’s has been used to examine tissue oxygenation in thin tissue sections or from surface reflection measurements. However, in the 1970’s the technique of near infrared spectroscopy (NIRS) of intact organs was first described by Frans Jobsis, a breakthrough that enabled truly non invasive measurements to be made on intact organs, allowing the technique to be applied to patients at the bedside. In the NIR (700-900 nm), oxygenation dependent changes in attenuation can be observed which arise from variations in the concentration of oxy and deoxyhaemoglobin in the blood, and of oxidised cytochrome oxidase in the cell mitochondria. Since the initial report of Jobsis, instrumental improvements now enable us to measure attenuation changes across many centimetres of tissue (most commonly brain or muscle), and techniques to quantify haemodynamic variables such as blood flow and volume have been developed.
Time- and wavelength resolved spectroscopy of photosensitizers in vivo using femtosecond white light
Authors: Klinteberg Claes af , Pifferi Antonio , Andersson-Engels Stefan , Cubeddu Rinaldo , Svanberg Sune
Published: February 2023

Knowledge on the absorption spectrum of photosensitizing drugs used in photodynamic therapy (PDT) is of great importance to optimise this tumour treatment modality. Many photosensitizers have an absorption maximum used for PDT in the red wavelength region. The spectral width of this peak is usually rather narrow, and the maximum often changes due to the chemical environment. For optimal treatment with a narrow-band light source such as a laser, it is thus important to gain information on the exact wavelength of the absorption peak inside the tissue.
The Science and Technology of Organic EL Displays
Authors: Hudson A. J.
Published: February 2023

For display applications, organic EL offers the possibility of efficient, low voltage, multicolour operation coupled with low production costs and robust design. Typical organic EL devices, as shown in figure 1, consist of several organic layers deposited between two electrodes The organic layers are usually deposited by vacuum sublimation1 or polymer spinning2. On applying a voltage across the device oppositely charged carriers are injected from the two electrodes and are transported to the recombination zone. The carriers then recombine forming excited molecular states which decay radiatively giving out emission with a characteristic spectrum.
Laser Cleaning of Radioactively Contaminated Surfaces
Authors: Steglich K.-H. , Harde H.
Published: February 2023

Within the scope of surface cleaning a Nd YAG laser seems to become a standard for cleaning of antiques, stone facades or other objects suffering from dust and environmental impacts Cleaning is understood as a process which eliminates buggy foreign bodies. The object of such process is to remove impurities or an upper layer covering the original surface without affecting or destroying the underlying structure.
Ultra Stable Solid-State Lasers
Authors: Man Catherine N.
Published: February 2023

Ultra-stabilized lasers have become an important issue playing a fundamental role in several applications such as metrology, high-resolution spectroscopy, gravitational wave detection or quantum electrodynamics tests.
DIAL Measurement of Atmospheric Water Vapor Profiles
Authors: Bösenberg Jens
Published: February 2023

Differential absorption lidar is a very powerful technique for the retrieval of trace gas profiles in the atmosphere. While it has been applied successfully for many trace gases like O3, NO2, NO, SO2, and many others for a rather long time already, the application to water vapor profiling had proven difficult due to the narrow linewidth of the water vapor absorption lines, and due to the rather high accuracy requirements in atmospheric research. With new achievements in laser technology the main restrictions have been overcome during the past years so that accurate measurements can be performed now.
A Compact Pulsed Coherent CO2 Laser Radar for Urban Meteorology
Authors: Pearson G.N. , Collier C.G.
Published: February 2023

Cities have a profound impact on the local climate, particularly upon wind flow and the distribution of precipitation, since they generate large land surface inhomogeneities which may lead to local wind circulations. Pulsed Doppler laser radar can provide unique data relevant to various aspects of these local climate issues. The inherent angular and spatial resolution, the ability to detect returns from ‘clear-air’ and the lack of ground clutter enables such systems to yield valuable information pertinent to a wide range of boundary layer and tropospheric phenomena.
A tunable UV-IR lidar system for atmospheric monitoring
Authors: Ambrico P.F. , Amoruso S. , Amodeo A. , Armenante M. , Berardi V. , Boselli A. , Capobianco R , Pappalardo G. , Spinelli N. , Velotta R. , Wang X.
Published: February 2023

A new tunable Lidar system, based on two Optical Parametric Amplifier (OPA) lasers pumped by a Nd:YAG laser operating at a maximum repetition rate of 100 Hz, has been designed to perform simultaneous measurements of atmospheric aerosols, water vapour and atmospheric pollutants concentration profiles [1]. OPA lasers, operating in a broad spectral range (350 - 2500 nm) with a very narrow line (<0.04 cm-1), allow to perform DIAL measurements in the whole UV-VIS-NIR spectral region Receiver consists of two different telescopes in newtonian configuration; two rotating plane mirrors located above each telescope act as a coelostat allowing a tridimensional mapping.
A Rayleigh lidar on rockets for studies of the middle atmosphere
Authors: Eriksen Torkild , Hoppe Ulf-Peter , Thrane Eivind V. , Blix Tom A.
Published: February 2023

Two new rocket-borne Rayleigh lidar experiments were developed at the Norwegian Defence Research Establishment and launched from Andøya Rocket Range in October 97 and January 98. The aim of the experiments were to measure the neutral atmosphere number density and to study the dynamics of the middle atmosphere. A simulation programme for calculation of Rayleigh-scattered signal, background level and noise was used to investigate the performance of the instrument. Various configurations of transmitters and receivers were evaluated. For the transmitter, laser diode arrays and solid state lasers were considered. The diode arrays were found suitable and two types of high power diode arrays were tested in the laboratory. A 20 bar array assembled using the bars-in-grooves technology was selected. It was operated in QCW mode with a pulse length of 450 μs, a pulse repetition rate of 135 Hz and an average optical power of 62 W at 805 ± 5 nm. It required a power supply giving 65 A at 42 V, active water cooling and a collimating lens. For the receiver, diodes and PMTs were considered. A large-area detector able to process photon rates of 106to 1010 s-1 was essential. An APD was selected due to the better quantum efficiency compared to the PMTs at 805 nm. It had a gain of 200 at 2.4 kV, and was cooled to -20°C to reduce the dark current to 1.5 nA and the rms-noise to 40 pA.
Intracavity Microchip Optical Parametric Oscillator
Authors: Fulop Ludovic , Fulbert Laurent , Molva Engin
Published: February 2023

We present a new concept for mass production of micro-OPO's pumped with microchip lasers. Microchip lasers are compact and simple diode-pumped solid-state lasers. They have a monolithic cavity with mirrors directly deposited on the laser material. Our concept is the association of a microchip laser without output coupler with a monolithic OPO (Fig. 1). The microchip laser and the OPO wafers are assembled using a novel process and the micro-OPO is cut using a dicing saw. In this configuration, the OPO benefits of the intracavity laser power to reach the oscillation threshold.
Absolute phase control of amplified femtosecond pulses
Authors: Dorrer C. , Le Blanc C. , Salin F.
Published: February 2023

Spectral phase modulation has been recognized as a powerful mean of generating arbitrary shaped waveforms in the temporal domain ([1], [2]) and of correcting spectral defects of Chirped Pulse Amplification systems ([3]), but results were always characterized by indirect means. We demonstrate here, for the first time to our knowledge, full phase control in an amplified system with arbitrary phase patterns using an absolute phase measurement at the output of the laser chain and a phase modulator at the input of the amplifier.
Self-mode-locked semiconductor laser in a ring cavity
Authors: Langlois Patrick , Piché Michel
Published: February 2023

We report on the generation of short (2 ps) pulses directly from a self-mode-locked semiconductor amplifier inserted in a ring cavity. The amplifier is in fact a superluminescent diode consisting of a 500 mm long double quantum-well InGaAlAs ridge waveguide with strained InGaAs active layers ; an angled stripe geometry provides a low coherence emission with a broad spectrum centered near 855 nm. The amplifier is placed in a ring cavity with three gold minors and a 83% transmission output coupler. Collimation of the laser output and careful alignment of the cavity mirrors allows laser emission with a threshold bias current Ith near 46 mA. Self-mode locking is achieved when the dc bias current is set at ~1.2 Ith, and when the cavity is slightly misaligned. Figures 1 and 2 show typical non-colinear autocorrelation traces and optical spectra of the pulses circulating in the clockwise (cw) and counterclockwise (ccw) directions. The counterpropagating pulses have similar temporal profiles with durations from 2 to 6 ps (after deconvolution) and characterized by a weak pedestal that falls to zero. Remarkably, the pulse respective optical spectra are different, as the spectrum of the ccw pulse has a 2.9 nm bandwidth peaked at 864 nm, whereas that of the cw pulse is peaked near 867 nm with a bandwidth of 0.9 nm. Both circulating pulses have a time-bandwidth product exceeding several times the Fourier-transformed limit, which suggests that they can be compressed to subpicosecond durations.
Cascade Acceleration of Photons front the Infrared to the Ultraviolet in Nonlinear Optical Media
Authors: Crespo H. , Mendonça J. T. , Santos A. Dos , Antonetti A.
Published: February 2023

Photon acceleration is a well understood mechanism in plasma physics. Here we describe a similar experiment using non-ionised optical media (glass). An intense and surprising effect occurs, which leads to a cascade of perfectly coherent and synchronised beams of different frequencies, ranging from the infrared (near 800 nm) to the ultraviolet (around 300 nm).
Adaptive optical applications of electro-optic devices
Authors: Love Gordon D.
Published: February 2023

Adaptive optics (AO) is an emerging technology used to correct aberrations in optical systems. It achieves this by spatial and temporally phase modulating the light, as opposed to image processing techniques which aim to deconvolve aberrations once an image has been recorded.
Making single crystal colloids for photonic bandgaps in the optical domain.
Authors: Kitson S.C. , Amos R. , Tapster P.R. , Rarity J.G.
Published: February 2023

We describe novel methods for making good quality colloidal crystals. We use polymethylmethacrylate (PMMA) spheres of diameter 0.8microns suspended in organic solvents between glass plates separated by about 10 microns. We have characterised the phase diagram in this confined system as a function of volume fraction and find that at volume concentrations beyond 49% a significant fraction of the suspended PMMA spheres are forced to crystallise into random close packed structures. The crystallite size is typically small (100microns) and the predominant structure is random close packed. This we confirm by single crystal light scattering measurements. We do find small areas of face centred cubic structure in these samples which we assume arises simply by chance stacking as the crystallites are typically only 10-15 layers thick. However the crystallite size can be increased simply by shearing the suspension during preparation. We also find conditions under which the formation of face centred cubic crystals can be preferential. We would present video footage of diffraction patterns formed during the shearing process where we can see clear evidence of the transition from random packing to FCC ordering.
Comparison of the efficiencies of dry and steam laser cleaning of silicon surfaces
Authors: Mosbacher M. , Dobler V. , Boneberg J. , Leiderer P.
Published: February 2023

As the structures on microelectronic chips are getting smaller and smaller, reaching the region of a hundred nanometers, the removal of submicroscopic particle contaminants on wafer surfaces becomes of increasing importance. Due to the strong influence of adhesion forces on small particles the conventional cleaning methods such as are inefficient. Recently it has been demonstrated that particles down to diameters of 200nm can efficiently be removed by laser cleaning [1].
Optical Waveguides in a-Si/SiO2 Submicrometer 3D Photonic Crystals: Fabrication and Observation
Authors: Hanaizumi Osamu , Ohtera Yasuo , Sato Takashi , Kawakami Shojiro
Published: February 2023

It is expected that optical circuits such as 90° bends [1] without radiation loss can be realized by using photonic crystals. In previous works [2, 3], however, it has been difficult to fabricate submicrometer three-dimensional (3D) structures larger than 4 periods. In this study, we have fabricated the 3D photonic crystal waveguides and observed propagation phenomena of the light beam for the first time.
In-Plane Modulation of non Linear Polymer Devices: Comparison of Electric, Photo-Assisted and Photoinduced Poling Processes
Authors: Donval A. , Toussacre E. , Brasselet S. , Zyss J.
Published: February 2023

Electrooptical polymer waveguide devices can be easily achieved by simple spin coating of polymer layers, with a transparent polymeric matrix as the passive buffer layer and with a side chain polymer as the active guiding layer. After deposition, the material is centrosymmetric, and therefore deprive of second order property. In order to create a noncentrosymmetric EO active material, a classical poling procedure may be adapted, whereby an electrical static field at elevated temperature, is applied over the side chain polymer resulting in the polar alignment of the chromophores parallel to the substrate.
Generation of 426 nm blue light in periodically-poled-flux-grown KTiOPO4 fabricated by a low temperature poling process
Authors: Eger D. , Oron M. B , Katz M. , Englander A , Rosenman G , Skliar A , Webjorn J.
Published: February 2023

Electric field poling has become a well-established technique to create in ferro-electric materials micro-domain structures inverted periodically for nonlinear optical conversion applications. This technique cannot be directly applied for flux-grown KTiOPO4, (KTP) due to its relatively high (super ionic) conductivity. By one recently developed method, the KTP wafers are chemically treated before the poling process to increase their resistivity.1
Long Wavelength Infrared Generation from 8-19 µm
Authors: Chen W. , Mouret G. , Cochie B. , burie J. , Boucher D.
Published: February 2023

New development of a broadly tunable continuous-wave (cw) infrared source is described. Long wavelength infrared radiation from 8-19 µm is produced by difference-frequency generation (DFG) in gallium selenide (GaSe) crystal. This, to our knowledge, is the first realization of cw DFG in GaSe up to 19 µm near its absorption edge.
Femtosecond Laser Microprinting of Metal and Oxide Structures
Authors: Papakonstantinou P. , Zergioti I. , Mailis S. , Ikiades A. , Kalpouzos C. , Vainos N. A.
Published: February 2023

Ultrafast laser microprinting is studied and presented. The microprinting technique utilised a femtosecond laser (λ = 248 nm, τ= 500 fs), and an imaging system to induce ablation of metal or oxide of a thin film source, transparent support/film interface and forward it to a receiving surface in close-contact as illustrated in figure 1 a. The investigation involves the ablative transfer of Cr and indium oxide materials. The receiving substrates used were glass, Si and MgO (100). Parametric studies were performed to investigate the dependence of feature spread profiles on the laser fluence and source film thickness.
Optically Recorded Diffraction Elements for Neutron Scattering
Authors: Rupp Romano. A.
Published: February 2023

Eight years ago we reported for the first time on neutron diffraction from holographic gratings written in light-sensitised poly(methyl methacrylate) [1] Since then, several improvements have been achieved: Replacement of a methyl group by nitrogen in poly(cyano acrylate) increases the coherent scattering amplitude by a factor of approximately 2.5 without significant deterioration of the amplitude of the light-optical holographic grating. Incoherent neutron scattering is further reduced by perdeuteration and the effect of the low lateral coherence of the neutron beams could be accounted for. By now holographic gratings with neutron diffraction efficiencies of more than 70 % for neutron wavelengths of about 4 nm can be produced. By exploiting the inherent nonlinearity of the kinetics of the photopolymerization process gratings with spatial frequencies of nearly 10,000 lines/mm have been achieved recently [2].
Neutron diffraction from higher harmonics of volume phase gratings in poly(methyl methacrylate)
Authors: Rupp R. A. , Havermeyer F. , Lyuksyutov S. , Eckerlebe H. , Staron P. , Vollbrandt J.
Published: February 2023

Elementary volume phase holograms can be recorded in poly(methyl methacrylate) doped with a photoinitiator using a holographic two-beam set-up. The photopolymerization process of the residual monomers in the polymer matrix turns out to be inherently non-linear. Consequently, illumination with a sinusoidal light intensity pattern results not only in a grating with the fundamental spatial frequency but also with higher harmonics. As the absorption of the photodoped material steeply rises for wavelengths below 320 nm, structures with periods below about 105 nm cannot be read out by light diffraction in Bragg geometry, the limit for Laue geometry is even 160 nm. This poses the following question: Can we induce gratings by light which are below the optical resolution limit by the non-linear recording mechanism and how can we prove it?
Investigation of atomic and molecular species in a Copper-HBr laser
Authors: Girard F. , Bertrand G. , Guyadec E.Le
Published: February 2023

Atomic copper production in aCu-HBr laser is not trivial. It results from a chemical heterogen reaction between gaseous hydrogen bromine and solid copper pieces. Our study deals with the processes governing the production of copper in the laser tube. It is associated with the copper feed lifetime as well as the volumetric efficiency.
Operation of the atomic xenon laser near 4μm
Authors: Wendland J J , Baker H J , Hall D R
Published: February 2023

The atomic xenon laser is an attractive candidate for remote sensing and other applications requiring low atmospheric absorption, due to the presence of a transmission window in the 3.5 - 4.2μm region. The xenon laser, configured with a non-dispersive resonator, produces a number of laser lines between 2.0-3.51μm when excited with a transverse radiofrequency discharge, with laser powers at the level ~5Watts. Experiments have shown that the gain in the atomic xenon laser is strongly dependent on the gas mixture, gas composition and pressure as well as the input RF power. Moreover, there are very strong competition effects, caused by the fact that many laser lines share either an upper or a lower level. These factors suggest the possibility of selecting a gas mixture which preferentially yields a higher laser gain for particular line at the expense of reduced gain for competitive lines.
Erbium doped Waveguide Amplifier in Glass Fabricated by a Hot-Pressing Technology
Authors: Graf J. , Sautter H. , Müller-Fiedler R. , GmbH Robert Bosch
Published: February 2023

Optical amplifiers are required for high bandwidth, low crosstalk transmission, especially in wavelength multiplexed configurations. Moreover integrated optical amplifiers are of special interest in access networks, providing services to thousands of customers, resulting in high numbers of low cost lossless splitters, realised by Y-branches and amplifiers.
Rare-Earth Doping of Active Waveguides by Pulsed Laser Deposition
Authors: Serna R. , de Castro M. Jiménez , Requejo J.M. , Afonso C.N.
Published: February 2023

In the past few years rare earth ions have played an important role in the progress of optical communication technology through the development of optical amplifiers. As optical telecommunication networks are well established today the challenge lies in the development of photonic circuits with devices integrated on a single chip for generating, switching, routing and amplifying optical signals. Thus active waveguides able to perform these functions have to be deposited on a planar substrate. Incorporation of rare earth ions (Er3+, Pr3+) in thin films permits the construction of planar integrated lasers and amplifiers operating respectively at 1.5 μm and 1.3 μm, the wavelengths of interest for communication purposes. Such incorporation has been achieved mainly by means of techniques that allow local doping, such as ion exchange, in diffusion or ion implantation. While these techniques have proven to be successful, they lead to non-uniform dopant profiles and require multistep processes. Pulsed laser deposition is a recently developed technique with a proven capability for growing complex oxides.1 It allows easily to deposit the matrix and dopant in a single step process, and leads to a uniform distribution of the dopant throughout the active region of the waveguide.2
Liquid Phase Epitaxy Grown One-Dimensional Waveguides of LiYF4 for Down- and Upconversion Laser Applications
Authors: Burkhalter R. , Hulliger J. , Müller A. , Rogin P.
Published: February 2023

Recently, we have demonstrated down-conversion laser operation in planar and linear Nd:LiYF4(YLF) waveguide structures grown by liquid phase epitaxy (LPE) [1,2]. However, a first device of a one-dimensional geometry was obtained by subsequent mechanical polishing steps followed by the growth of a cladding layer. Substantial improvement seems possible by an exploration of different surface structuring techniques in order to reduce the cross-section down to about 5×5 μm at a length of 1 to 1.5 cm. Current work to be presented includes (i) an exploration of chemical polishing agents, (ii) ion etching or laser ablation for a pre-(I) or post­structuring (II) procedure. Further activities comprise high energy ion implantation. YLF substrates are obtained by a vertical gradient freezing technique. Because of the phase diagram of pure YLF, the process of LPE is restricted to operate rather at a low ratio of LiF / YF3 varying in the range of 3/2 to about 1/2. Controlling the thickness of an active layer down to ~5 μm is hence demanding with respect to the control of temperature (ΔT < 0.5 - 1.0 °C). Because of this the present LPE approach includes one polishing step (see I, II). An alternative avoiding polishing at any intermediate step would lower the YLF concentration in the liquid phase in order to decrease the growth speed (LiF/LiCl-flux).
High-power operation of strained GaInP/AlGaInP quantum well laser diodes grown by solid source molecular beam epitaxy
Authors: Toivonen M. , Savolainen P. , Orsila S. , Dumitrescu M. , Pessa M. , Corvini P. , Fang F. , Finander M. , Nabiev R. F. , Jansen M.
Published: February 2023

High power 600-nm-range AlGaInP-based laser diodes are attractive light sources for various applications, such as photodynamic therapy, optical pumping of tunable solid-state lasers, projection displays, bar-code readers, and high speed printers. The reliability of AlGaInP-based lasers has been a widely debated issue lately. In order to achieve reliable high-power operation of lasers in the red, low-threshold and high efficiency operation should be established. This could be achieved by using strained active regions and by optimizing the growth conditions for the laser material. In addition, proper laser structure design and facet coating procedures are indispensable to increase the maximum usable output power before the catastrophic optical damage takes place.
Improvement of the Efficiency of the Conversion of the Discharge Energy into the Emission of Excimer Molecules in Mixtures of Mercury Dihalides and Rare Gases of Excimer Lasers
Authors: Malinin A.N.
Published: February 2023

Complex investigations have demonstrated that the

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states of mercury monohalides are efficiently excited in a pulse-periodic glow discharge through a dielectric at atmospheric pressures of mixtures of mercury dihalides with rare gases [1].
Demonstration of 2.488Gb/s simultaneous all-optical wavelength conversion and tone reading/replacing in an integrated SOA/DFB laser
Authors: Stephens MFC , Bainbridge JD , Owen M , Penty RV , White IH , Fice MJ
Published: February 2023

Wavelength division multiplexing is established as an important technique for employing the large bandwidth of optical fibre. There exists a need for a simple wavelength identification scheme to allow recognition of individual wavelengths in the network. One technique which has been proposed is the use of low-frequency pilot tones [1]. In this scheme, each wavelength channel is coded by a different tone frequency. To allow wavelength identification at any point in the network, a small proportion of the optical power in a fibre may be simply be tapped off and detected by a photodiode. The pilot tones can then be filtered electrically and their frequencies and levels registered. If wavelength conversion is also required in the network, the pilot tone for that signal must be removed and replaced with a new one representing the translated wavelength. Here we demonstrate, for the first time we believe, a novel technique for all-optically wavelength converting and simultaneously monitoring and replacing a pilot tone using a single integrated device at 2.488Gb/s.
Soliton interaction reduction in the transmission of solitons generated by direct modulation of laser diodes
Authors: Revuelta J. , Pesquera L. , Mirasso C. R.
Published: February 2023

We have numerically shown that pseudorandom sequences of solitons can be generated by direct modulation of laser diodes (LD) when biasing slightly below threshold [C. R. Mirasso et al, IEEE Photon. Tech. Lett. 7, p. 437, 1995]. Using this bias current pattern effects are avoided and the fluctuations originated in the LD are reduced. In this way electroapsorbtion modulator are not necessary to codify the message.
A novel all-optical demultiplexing scheme based on the fiber nonlinear optical loop mirror
Authors: Xiang Zhou , Ye Peida
Published: February 2023

The fiber nonlinear optical loop mirror (NOLM) is widely used in the OTDM demultiplexing, because it has the potential of operation at the extreme high bit rates. For traditional NOLM (only one control beam), however, timing jitter between the clock and the signal and crosstalk mainly arising from the unwanted cross-phase-modulation (XPM) in the reference signal will seriously degrade the BER performance [1].
High Performance DWDM Multiplexer and Demultiplexer With a 0.4 nm Channel Spacing
Authors: Pan J. J. , Shi Y.
Published: February 2023

With an ever increasing demand for bandwidths in lightwave communication networks. DWDM with a channel spacing of ≤0.8 nm plays an important role. This requires DWDM devices with a flat-top transmission spectrum, a high channel isolation and low insertion loss for the EDFA flat gain wavelength range [1]. In this paper, DWDM devices with a 0.4 nm channel spacing using apodized FBGs and bandpass WDM filters (BWDM) in cost-effective structures are demonstrated.
Optimisation of a reconfigurable free-space fibre switch in the WDM 1,55 µm window
Authors: Fracasso Bruno , Berthelé Patrick , de Bougrenet de la Tocnaye Jean-Louis
Published: February 2023

In the framework of optical transport networks based on wavelength division multiplexing, (WDM), one of the most critical elements is the optical cross-connect [1] (OXC). At the core of many cross-connect architectures is a space-switching stage, operating in the 1.55 telecom wavelength window. An important feature is that the device routing peformance must be polarisation insensitive, with moderate insertion loss and reconfiguration rates lower than the microsecond.
Investigation of the Singlet Oxygen Generator with the Twisted Flow
Authors: Vyskubenko B.A. , Krukovsky I.M. , Adamenkov A.A. , Deryugin Yu. N. , Ilyin S.P. , Kudryashov E.A.
Published: February 2023

The experimental and theoretical investigations results of the Aerosol Singlet Oxygen Generator with the Twisted flow (TASOG) intended for supersonic high pressure Chemical Iodine - Oxygen Laser (COIL) are presented. TASOG output flow parameters are studied at different reaction zone lengths, with inner gas velocities up to 40 m/sec, and pressures up to 90 Torr. The stable available TASOG model operation range without aerosol carrying out is defined and all characteristics presented apply to this very case. The singlet oxygen flux value through the output cross section unit at the reaction zone as much as 6 mmol/sec×cm2 or electron energy flux more than 500 Wt/cm2 are achieved. The TASOG output increasing ways are discussed.
Effects of the phase difference between the coupling constants upon the threshold characteristics of nonuniformly complex-coupled distributed feedback devices.
Authors: Fessant Thierry
Published: February 2023

Purely index-coupled distributed feedback (DFB) lasers are well-known components with practical application as optical sources in telecommunication networks using wavelength division multiplexing. Unfortunately, spatial hole burning makes them somewhat problematic above-threshold so that more complicated multisection structures (with multiple phase shifts, phase adjustment region or distributed coupling coefficient for example) have to be designed. On the other hand, gain coupling mechanisms in Bragg gratings attract attention from many research groups and promising devices are expected. Such complex-coupled DFB (CC-DFB) structures have already been studied through the relative amount of gain and index couplings, assuming a fixed phase difference between the two contributions (generally 0 or π) [1]. On the other hand, by lifting the restriction of this fixed phase difference, conventional CC-DFBs have been found to exhibit various interesting and useful properties [2] but, to date, nonuniformly complex-coupled (NCC-DFB) devices have not been addressed.
Second harmonic generation in powder laser
Authors: Noginov M. A. , Egarievwe S. U. , Noginova N. , Wang J. C. , Caulfield H. J.
Published: February 2023

A laser-like emission from powders of solid state luminophosphors was reported in a number of publications, see for example Refs. [1,2]. A dramatic narrowing of Nd emission line (4F3/2-4I11/2) in powders of Nd doped laser materials is observed when the pumping energy exceeds some critical threshold value. At the same time, a series of short (0.3-1 ns) 1.06 μm emission pulses appears in response to 10-30 ns pumping pulse. In the present paper we report second harmonic generation in a powder laser based on a mixture of Nd0.5La0.5Al3(BO3)4 and 2-methyl-4-nitroaniline (MNA). We excited the powders with 10 ns laser pulses at 580 nm. The pumping beam was focused to 0.02 cm2 spot. Under intense pumping, short pulses (typical for Nd powder lasers) were obtained at 1.06 μm in the mixtures of powders and in pure Nd0.5La0.5Al3(BO3)4. Simultaneously, 0.53 μm second harmonic radiation was observed in mixed samples. The slope of the dependence of 0.53 μm light intensity, I0.53, on 1.06 μm light intensity, I1.06, [Ln(I0.53) vs Ln(I1.06)] is equal to 2. We have shown that the threshold of the powder laser stimulated emission increases and the slope efficiency decreases with the increase of MNA concentration in the mixture, Fig. 1.
Investigation of the frequency-doubling efficiency saturation in periodically poled KTP
Authors: Pasiskevicius V. , Pierrou M. , Wang S. , Tellefsen J. A. , Laurell F. , Karlsson H.
Published: February 2023

Periodically poled KTP (PP-KTP) crystals offer a number of features, such as phase-matching with the highest nonlinear coefficient, low temperature sensitivity and relatively high optical damage threshold, which make them attractive for extracavity and intracavity frequency doubling (FD) of the Nd - doped laser hosts. Recently, we have demonstrated 66 % extracavity FD efficiency of the Q-switched Nd.YAG laser by using periodically poled flux-grown KTP [1]. Our investigations show that the FD efficiency in PP-KTP is about two times higher than in conventional type-II phase-matched KTP. Moreover, the measured optical damage threshold for the PP-KTP was more than 1.5 times higher than in conventional KTP.
Optical wavelength switching by stimulated Raman scattering in a single-mode fiber
Authors: Sylvestre T. , Maillotte H. , Lantz E.
Published: February 2023

Stimulated Raman scattering (SRS) in optical fibers has been mainly used for broadband amplifiers, tunable fiber lasers or pulse compressors1. All of theses applications dealt only with the downshifted Stokes frequency ωs=ωp−ΩR where amplification of a weak signal copropagating with a pump occurs when the signal wavelength falls in the Raman gain bandwidth. In the present work, we launched a weak signal pulse at the anti-Stokes frequency ωas=ωp+ΩR along with the pump (fig. 1-a). Experimental results performed in the visible domain show a strong attenuation of this anti-Stokes signal (fig. 1-b) with an efficiency of-20 dB (fig.2-a) and the simultaneous conversion to a Stokes pulse (fig. 1-b) amplified exponentially with respect to the anti-Stokes input with a maximum gain of 15 dB (fig.2-b). In the absence of the input anti-Stokes signal, no Stokes ouput is detected for the same pump power level as in fig. 1-b which is below the usual stimulated Raman threshold of the fiber1.