bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient, single frequency LiF:F 2 − laser
Authors: Diettrich Jan C , McKinnie Iain T , Warrington Don M , Ter-Mikirtychev Valerii V
Published: February 2023

Tunable, single mode, solid state lasers are required for many spectroscopic and remote sensing applications in the near infrared region. Although the important wavelength range between 1.05 and 1.3 µm is only covered by colour centre lasers, widespread use of

LiF:F

2
−

lasers has been limited by relatively low crystal quality, passive loss and

F
2
−

photodegradation processes. Narrowband

LiF:F

2
−

lasers have, consequently received little attention [1], operaring with low efficiency and poor long term stability. However, the recent development of crystals containing more stable

F
2
−

centres as well as improved crystal irradiation and annealing techniques have led to increased operating lifetime and laser efficiency [2]. (We have observed no degradation in laser performance during seven months of operation). Here we demonstrate efficient single frequency operation using a recently-developed

LiF:F

2
−

rod in an innovative dual cavity configuration. We anticipate that this resonator will be widely applicable to other laser media.
Recent advances in Doppler Wind Lidar technology at the European Space Agency
Authors: Marini A.E. , Gonte F.
Published: February 2023

The importance of global and accurate wind observations for meteorology and climatology has been unanimously recognised by the science community. In response to this need, the European Space Agency (ESA) is involved since the early 90’s in the definition of an European satellite-borne Doppler Wind Lidar (DWL) system, aimed at enhancing the validity of numerical weather predictions and. more generally, to improve our knowledge of the atmosphere. Such a DWL instrument is now planned for demonstration in orbit from the International Space Station Alpha, within the forthcoming ESA Earth Explorer Atmospheric Dynamics Mission, in the running study phase of the mission, the original concept based on CO2 laser technology shall be compared and contrasted with more recent instrument concepts based on solid-state laser technology. In fact, ESA is now considering solid-state DWL’s as valuable alternatives. Definition studies and critical technology developments are currently being carried out on incoherent DWL concepts based on interferometric detection technique and Nd:YAG laser and on a coherent DWL concept based on heterodyne detection and Tm.Ho:YAG laser.
Ablation Products from UV-Laser Irradiated Polymer Surfaces Deposited onto Different Substrates
Authors: Arenholz E. , Klose S. , Kirchebner A. , Heitz J. , Bäuerle D.
Published: February 2023

Some effects of UV-laser ablation of polymeric materials are well studied. Among them are material removal, the formation of self organized periodic surface structures in the nano- and micrometer range and the ablation process itself1. This contribution will focus on the relatively new field of deposition of ablation products both onto an extra substrate (pulsed laser deposition) and back onto the laser irradiated sample (re-deposition). In a detailed study it was observed that this type of material is of high importance in different fields such as the laser induced permanent conductivity enhancement of polyimides, the formation of branched self-similar surface structures (dendrites) on polyesters and on the pulsed laser deposition of PTFE (Teflon™). We want to present new results on such deposited surfaces investigated by XPS, AFM, SEM, RBS, IR- and UV-Vis- spectroscopy. The formation of carbon nano-wires (about 80 nm wide and several micrometers long) on polyimide substrates will be demonstrated and explained on the basis of carbon nano-clusters redeposited and/or formed on the surface. The well defined nano-roughness of several 10 nm in height covering the whole irradiated surface area of PET (Fig. a) will be discussed on the basis of ablation products redeposited and partly embedded into the amorphized ablation area. Sperulitic crystal growth (Fig. b) in laser-deposited PTFE-films onto silicon substrates will be examined2 and their relation to the good electrical quality of these films with low dielectric constant and low conductivity together with high thermal stability will be discussed.
All Optical Multiplexing-Demultiplexing of Low-Intensity Pulses
Authors: Fazio E. , Biraghi A. , Sibilia C. , D’Aguanno G. , Bertolotti M. , Cojocaru C.
Published: February 2023

It is well known that it is possible to obtain all-optical switching by using the nonlinear response of materials to laser light, but it is also well known that to excite nonlinear contributions high local-electric fields are necessary. This means that high-intensity laser beams must be used for having switching of photonic devices between different states. On the same time it has been largely demonstrated both theoretically and experimentally that in optical fibers only low intensity beams can propagate for communication purposes, even in the case of solitonic beams, where the average powers should not be larger than few tens of mW. Thus until now no real applications of the proposed photonic devices have been done in real fiber communication networks. In the present paper we present from both the theoretical and the experimental points of view an all-optical multiplexer-demultiplexer for low-intensity pulses. In particular the devices has been projected to work for high-repetition rate mode-locked pulses, 100 and 35 ps long, with average powers of the order of few tens of mW. The device is working at the wavelength of 1.064 μm because of testing possibility, but there are no obstacles to let it work at 1.3 or 1.5 μm. The device is based on a thin Fabry-Perot cavity filled by a second-order nonlinear material. In particular it has been chosen a BBO with type I cut for second harmonic generation of 1.064 μm pulses. The basis of operation are the generation-amplification of the second harmonic. In particular the Fabry-Perot cavity is set out-of-resonance for the fundamental frequency: because of its low intensity the fundamental is not able to produce a relevant second-harmonic field and for this reason does not modify its out-of-resonance regime. However if a high-intensity second-harmonic field is sent together, the fundamental beam can be amplified, experiencing a phase-modulation which depends on the group-velocity mismatching between the frequencies and their intensity ratio. This cross-phase-modulation can be high enough to let the fundamental frequency switch from the out-of-resonance to the resonance regimes. In fig.s 1 and 2 the out-of-resonance / resonance conditions are shown respectively.
High Power 3×3 VCSEL Array
Authors: Miller M. , Grabherr M. , Jäger R. , Martin U. , Ebeling K.J.
Published: February 2023

Vertical cavity surface emitting lasers (VCSEL) have become superior devices for various applications in data transmission, especially parallel optical interconnects. Their output power is limited to a few mW due to the small diameter of about 10 μm and thermal rollover. To obtain higher optical power one can increase active size of a single laser at the cost of decreasing wallplug efficiencies [1] or switch to two-dimensional arrays which provide high output powers at still high conversion efficiencies.
63% wall-plug efficiency InGaAs/AlGaAs broad-area laser diodes and arrays
Authors: Heerlein J. , Schiehlen E. , Jäger R. , Unger P.
Published: February 2023

High-power large-area multimode laser diodes are important for a wide range of applications. In this work, we present our improved epitaxial quality in terms of efficiencies, intrinsic losses, far-field angles and differential resistances. Therefore, gain-guided broad-area laser diodes and arrays mounted junction-side down on diamond heat spreaders have been fabricated and investigated.
Unifused Broadband 1×N and N×N Fiber Optic Couplers
Authors: Pan J. J. , Zhou Feng Qing , Huang Yong
Published: February 2023

WDM fiber optic networks, both in 1.3 pm and 1.55 µm transmission windows, demand mass producible, low cost, low excess loss, wideband, monolithically fused miniature 1×N and N×N couplers for various system applications. Conventional approaches arrange fibers in equilateral polygon shape in a capillary to make 3×3, 4×4, 7×7 or 19×19 fiber couplers. To attain wide bandwidth, complicated fiber preparation processes such as pre-pulling, pre-etching or pre-deposition are required. To eliminate such shortcomings, a systematic theoretical analysis was performed on 1×N and N×N couplers, and a new monolithical fabrication method had been developed.
High Precision Phase Mask Without Stitching Error
Authors: Pan J. J. , Shi Y. , Zhou F. Q.
Published: February 2023

Phase mask (PM) is proved to be one of the most versatile techniques for massive production of FBGs for different applications [1]. FBG parameters can be controlled by designing control of PM's parameters. In this paper, PM production technique using precision e-beam writing and reactive ion-milling (RIM) techniques with advantages of stitching error-free and accurate period.
Optical Limiting Action of Methano Fullerenes and Fullerenes Incorporated in Cyclodextrins
Authors: Koudoumas E. , Couris S. , Seta P. , Rassat A. , Leach S.
Published: February 2023

C60 dissolved in organic solvents is known to exhibit important nonlinear optical response leading to strong optical limiting action. However its solubility is very poor in most of the organic solvents and practically negligible in water. The fullerene molecules are indeed very hydrophobic compounds with a great tendency even in organic solvents to form aggregates. Among the main routes explored to modify their solubility and properties and in order to prevent aggregation, is their insertion in host matrices such as polymer, zeolites or complexing agents such as γ-cyclodextrins and calixarenes).
Phase conjugation of red light with Sn2P2S6 crystals
Authors: Shumelyuk A. , Odoulov S. , Brost G.
Published: February 2023

Sn2P2S6 crystals ensure a rather high two-beam coupling gain factor (Γ ≥ 10 cm-1) and relatively short relaxation time (τ ≈ 5 ms) with radiation of He-Ne laser [1], they are sensitive also up to λ = 1.3 μm. In this report we present the data on phase conjugation of He-Ne laser beams in backward-wave four-wave mixing geometry and with the self pumped conjugator based on the ring-loop photorefractive coherent oscillator.
Holographic Measurements of Photopolymers for Microstereolithography Applications
Authors: Farsari M. , Huang S. , Young R. C. D. , Heywood M. I. , Chatwin C. R.
Published: February 2023

In order for a resin to be suitable for stereolithographic applications, it must have a high curing speed, high build resolution and low shrinkage during the liquid to solid polymerisation process. (1). We performed nondegenerate four-wave mixing on two UV curable resins, the DuPont Somos™ 6100 and the Ciba-Geigy Ciba- tool™ SL 5180. Gratings with spatial wavelength Λ=0.3 - 1.1 µm were written using an Argon ion laser operating on the λ0=351.1 nm line and for a range of irradiance 0.5-3 W/cm2. The gratings were then read using a He-Ne laser, operating at 632.8 nm. These experiments were carried out to prove the suitability of the photopoly, nerisation systems for microstereolithography.
Photoacoustic investigation of the excimer laser ablation of YBa2Cu3O7−x HTSC
Authors: Dogas D. , Andreouli C. , Efthimiopoulos T. , Campbell M. , Savakis C.
Published: February 2023

The photoacoustic response of the YBCO high Tc superconductor has been monitored in order to investigate the interaction of the XeCl excimer laser nanosecond pulses with bulk YBCO targets. The detection and monitoring via a piezoelectric transducer of the compression of the laser induced pressure waves propagating into the bulk YBCO samples provides information regarding the vaporization and ablation thresholds, the velocity of the pressure wave and the etching rate.
New Excitation Regimes and Pump Modes for Discharge Excimer Lasers
Authors: Fedorov A.
Published: February 2023

In this review, a possibility of efficient quasi-stationary excitation regime is shown basing on experimental data obtained by the author and by other research groups. This regime is provide by multi-circuit excitation schemes with different UV sources and results in long optical pulses [1,2]. The self-sustained discharge is necessary to obtain this regime depending from buffer gas, discharge current density, duration of UV-pulse and resonator. Multi-circuit excitation circuits with automatic stabilized preionization sources and back up. For instance, in Ne-based mixtures three-circuit scheme provided "multi-pulse" regime for XeCl-laser. It was shown that both fast and quasi-stationary excitation regime can be observed by connection of preionization source to the primary of secondary circuit. However, the duration of discharge in the case of quasi-stationary excitation regime is determined by duration of UV-preionization pulse. General requirement for laser operation with different pumping circuits and UV-sources are formulated and physical model of processes involved in discharge kinetics in the quasi-stationary regime of excitation and lasing is proposed.
Short Time Process Observation During Laser Remelting of Aluminium Diecast Alloys
Authors: Haferkamp H. , Goede M. , Thürk O.
Published: February 2023

Rapid solidification of aluminium alloys during the remelting process using high power laser radiation results in refining effects of the solidified grain texture and improved wear resistance and material hardness. High temperature gradients can be achieved as well as energy coupling into the aluminium alloy is locally restricted, and can be precisely controlled. For the adjustment of defined grain textures, the dynamic behaviour of the melted material on the irradiated material surface is of high interest. Most of the optical set-ups currently used for process visualisation only image the plasma formation within the laser beam interaction zone. Available systems for frequency-selective irradiation and visualisation provide insufficient time resolutions with respect to rapid melting and solidifying processes.
Relative intensity noise induced by fibre dispersion at zero-dispersion wavelength in singlemode fibres
Authors: Cartaxo Adolfo V. T. , Morgado José A. P.
Published: February 2023

The relative intensity noise (RIN) induced by fibre dispersion slope has been indicated as a detrimental effect in very long broadband linear transmission systems operating at the zero-dispersion wavelength since the RJN may increase strongly with frequency and transmission length [1]. In this paper, we show theoretically and numerically that the transmitted RIN spectrum over singlemode fibre at zero-dispersion wavelength is similar to the RIN spectrum at the fibre input.
The Conception for Creation of Industrial High-Power Lasers with Continuous Formation of CO Mixture and RF Discharge in a Supersonic Flow
Authors: Baranov I. Ya.
Published: February 2023

Now the possibility for creation of industrial laser with power 20÷100 kW is associated with scaling of CO2 lasers. However, the increase of laser beam path between mirrors brings to degradation of optical beam quality. This is due to the fact that the quantum efficiency of CO2 molecule is 0,41 and also in a resonator the vibrational energy is converted to heat.
Novel substrates for GaN Epitaxy
Authors: Beaumont Bernard , Gibart Pierre , Faurie Jean-Pierre
Published: February 2023

Nitride semiconductor alloys have emerged as the most promising materials for short wave lengths ligth emitting diodes (LEDs) and laser diodes (LDs). The GaInN multiquantum wells (MQW) structure was used as the active part of LDs and have presently proven to work at room temperature for 10 000 hrs. These achievements would have not been possible without the emergence of new approaches in heteroepitaxy of GaN leading to layers zexhibiting lower dislocations densities than those grown using conventional heteroepitaxy. With the Epitaxial Lateral Overgrowth (ELOG), high quality GaN layers have been obtained. Consequently, laser diodes structures were grown on these new generation of substrates.
Pulsed laser deposited (PLD) GaN and its powder precursor
Authors: O'Donnell K P , Middleton P G , Trager-Cowan C , Cole D , Cazzanelli M , Lunney J G
Published: February 2023

Pulsed laser deposition offers a fast and convenient route for preparing crystalline GaN thin films that may be used either directly in devices or as substrates for conventional growth. 3 Jcm-2 pulses from an excimer laser impinge upon a rotating compressed powder target immersed in a nitrogen or ammonia atmosphere. The resulting ablated plume of material sublimes on a heated sapphire substrate to form the PLD layer. We report here a comparitive study of PLD films and their powder precursor by low temperature photoluminescence (PL) spectroscopy and cathodoluminescence (CL) imaging.
Characteristics of Anti-Resonant Fabry-Perot Saturable Absorbers for Laser Modelocking Produced by Metal Organic Chemical Vapour Deposition and Ion-implantation
Authors: Lederer Max , Luther-Davies Barry , Tan Hoe , Jagadish Chennupati
Published: February 2023

In recent years the generation of ultra short laser pulses in the near-infrared has been achieved mainly through the use of Kerr Lens Mode-locking (KLM). However, the main drawback of KLM is the need for starting aids except for highly optimised cavity designs where self-starting is possible. One starting mechanism that has been used successfully in KLM lasers is the saturable nonlinearity of a semiconductor Anti-resonant Fabry-Perot Saturable Absorber (A-FPSA) [1]. Several different A-FPSA designs have now been used to modelock broad band laser materials like Ti:Sapphire, Cr:LiSAF and Nd:glass by mechanisms other than KLM, with the A-FPSA as the sole passive modulator (e. g. soliton mode-locking).
Quantum well wires using As implantation induced intermixing in GaAs/AIGaAs
Authors: Ooi B S. , Helmy A. Saher , Tang Y.S. , Bryce A. C. , Marsh J.H. , Paquette M. , Beauvais J.
Published: February 2023

Low dimensional structures such as quantum well wires and quantum dots have attracted much interest in the past few years.1 Quantum well intermixing is one of the promising techniques for fabricating such structures, as opposed to the conventional techniques of dry-etching2 and metal-organic vapour phase epitaxy selective growth.3 For the GaAs/AIGaAs system, Ga and As, being native matrix elements, are the most promising ions for implantation. Low dimensional structures formed using Ga implants have been reported.4 In this paper we report the fabrication of GaAs/AIGaAs quantum well wires using implantation of As at 45 keV to induce quantum well intermixing. The intermixing process was first characterised giving optimised annealing parameters of 875°C for 30 s and an implantation dose of 1× 1013 cm-2. Wire widths from 35 nm to 1000 nm were defined using e-beam lithography followed by lift-off, where SrF2 was used as a mask for implantation and annealing. Photoluminescence spectra from the non-intermixed regions, lateral wells, and the intermixed regions, barriers, were observed from samples with wires as narrow as 50 nm. The energies of the lateral wells were found to remain constant for wire widths between 1000 nm and 150 nm, and start to shift significantly towards high energy for 80 nm wires, showing 1-D confinement effects. The signal from the lateral well eventually merges with that from the lateral barrier for 35 nm wires, as can be seen in Fig. 1, hence an intermixing radius of about 17 nm was estimated for the process. Photoreflectance measurements were also carried out on these wire samples, showing that the wires appear to have a parabolic lateral potential and clear interwire coupling was observed from samples with barriers narrower than 50 nm, as can be seen in Fig. 2.
Excimer Laser Corneal Shaping System: Principles, Realization and Clinical Applications
Authors: Husinsky W. , Homolka P. , Biowski R. , Blaas C. , Baumgartner I. , Grabner G.
Published: February 2023

Corneal grafts are needed in ophthalmology for curative surgery on a regular basis. Thus transplants are often used in connatal abnormalities like a dermoid, to replace scarred tissue or in healing dystrophical defects like pemphigoid. There are several possibilities for their production, the most common being mechanical shaping and cutting of donor tissue.
Afterglow Ground-State Copper Density Behaviour in Kinetically-Enhanced Copper Vapour Lasers
Authors: Mildren R.P. , Withford M.J. , Brown D.J.W. , Carman R.J. , Piper J.A.
Published: February 2023

The use of halogen donor additives in conventional high temperature (1500°C) copper vapour lasers (CVLs) has recently yielded significant enhancements in laser performance. Using a technique called ‘kinetic enhancement’ (KE), H2 and HCl buffer-gas additives have been found to increase the output power ~3× that observed for the same device operating with pure neon buffer-gas. For a 38mm bore CVL, it was shown that using H2-HCl-Ne gas mixtures increased output 1.5× and 1.3× that when using pure Ne and Ne with H2 additive respectively at the nominal CVL pulse repetition frequency (PRF) of 6 kHz. When increasing PRF, output increased linearly up to 22 kHz at which point the output power (150W) corresponded to 2.8× and 2.3× the maximum output power recorded for the tube when operated with either neon buffer-gas without or with hydrogen additive (53 W and 65 W respectively). In addition to the output power increases, the spatio-temporal characteristics of the KE-CVL
Hybrid integrated 4x4 matrix optical switch using silica based planar lightwave circuit
Authors: Shimoda T. , Sasaki J. , Kato T. , Hatakeyama H. , Tamanuki T. , Kitamura N. , Yamaguchi M. , Itoh M. , Kitamura M. , Kitamura S.
Published: February 2023

Hybrid integration of semiconductor optical amplifier gates (SOAGs) onto a silica based planar lightwave circuit (PLC) platform is one of the most suitable way to realize a matrix optical switch with high extinction ratio and nanosecond switching time. For the hybrid integration, it is highly desired that V-grooves for optical fiber assembly and signal transmission lines can be formed on a PLC platform with high quality optical circuits. In this paper, we demonstrate the successful operation of a hybrid integrated 4x4 matrix optical switch module. The PLC platform, with V-grooves for optical fiber assembly, and signal transmission lines, has been fabricated by low temperature process of TEOS/O3
In-Plane Diode-Bar Pumped, Multi-Watt, Nd:Y3Al5On Planar Waveguide Lasers
Authors: Bonner C.L. , Brown C.T.A. , Shepherd D.P. , Clarkson W.A. , Harris R.D. , Tropper A.C. , Hanna D.C. , Ferrand B.
Published: February 2023

There is a growing interest in using planar waveguides for high-power diode-pumped laser devices due to their geometrical compatibility with diode-bars and good thermal management capabilities. Here we report on our progress in constructing and characterising diode-bar, end and side-pumped Nd:YAG waveguide lasers.
Hybridisation Issues for Optoelectronic Components
Authors: Crean G.M. , Paineau S. , Corbett B. , O’Connell D. , Rodgers K. , Stain F. , Kelly P.V. , Redmond G.
Published: February 2023

In the absence of a truly integrated silicon optoelectronics technology, III-V components are likely to be an indispensable part of optoelectronic integrated systems for the foreseeable future. The development of manufacturable hybridisation technologies for III-V optoelectronic components, compatible with silicon and CMOS substrates, is therefore an essential research topic. In this paper, a review of current and emerging hybridisation technologies for optoelectronic components is presented. Technologies relevant to optoelectronic component hybridisation, including substrate removal, epitaxial lift-off, component alignment techniques, bonding and wiring processes are reviewed. Emerging novel self-assembly technologies, based on molecular tagging and recognition approaches, are also introduced. The state-of-the-art in hybridisation technology is reviewed with reference to recent US and European developments.
Manufacturability-compatible R&D in optoelectronics
Authors: Mukherjee Sayan D
Published: February 2023

The nature of research and development in optoelectronics has changed quite rapidly over the last years due to several reasons. Some of them are the maturing of the technologies, the gradual transition of research roles at Universities into R&D roles at industrial laboratories, the impatience amongst industries that invested continually over many years to reap the benefits in ROIs (return on investments), and last but not the least, realization of the existence of the tremendous cost barriers in optoelectronic packaging and implementation methods that have forbade large volume use of optoelectronics so far.
Yb:YAG fiber laser
Authors: Griebner U. , Schönnagel H.
Published: February 2023

The development of miniaturised diode pumped solid-state laser systems has received much attention due to their enormous potential for widespread applications. Consequently there is a great interest in fiber lasers based on crystal hosts, despite the technological difficulties to draw such fibers. Composite structures of thermally bonded crystals offer the prospect to manufacture short multimode crystal fibers.
Efficient, low threshold, collinear and noncollinear BBO optical parametric oscillators
Authors: Oien AnnMarie L , McKinnie Iain T , Jain Piyush , Russell Noah A , Warrington Donald M , Gloster Lawrie A W
Published: February 2023

High power, broadly tunable visible and infrared sources based on optical parametric oscillators (OPOs) and difference frequency generation (DFG) are being developed for applications in areas such as remote sensing, lidar and spectroscopy. In may cases these sources are based on critically phase-matched (CPM) processes in highly biréfringent materials such as ß-barium borate (BBO). OPO operating efficiencies, particularly in the high power regime, are limited by crystal acceptance angles and Poynting vector walkoff of e-polarised beams. Recent results1,2 indicate that improved operating efficiencies can be achieved using noncollinear CPM configurations. Poynting vector walkoff compensation (PVWC) and increased pump crystal acceptance angle at the onset of tangential-phase-matching (TPM) have been proposed as possible mechanisms for the enhanced operation.
Dental Er:YAG laser system
Authors: Jelínková Helena , Dostálová Taťjana , Miyagi Mitsunobu , Wang You , Shi Yi-Wei , Hamal Karel , Krejsa Otakar , Kubelka Jiří , Procházka Stanislav
Published: February 2023

The summarization of the results which were obtained with the constructed ErYAG dental laser system (500 mJ maximum energy and 200 μsec length of pulses) whose radiation interacts with the hard dental tissue are presented. The influence of the increasing energy and number of pulses on a profile and depth of drilled holes was investigated when the laser radiation delivery system were an articulated arm or a fluorocarbon polymer coated silver hollow glass waveguide. Also the test with the cutting speed were made.
Inactivation of Staphylococcus aureus and Escherichia coli with high-power Nd:YAG laser and UV radiation
Authors: Yeo C B Allen , Watson Ian A , Stewart-Tull Duncan E S , Armstrong Graham N
Published: February 2023

Recently, medical and dental applications of lasers have been increasing due to their non-invasive and selective characteristics. This includes for example, drilling teeth and removing port wine stains. Laser inactivation processes have been previously studied [1,2]. Ultra-violet radiation processes are well known, in which thymine dimers inhibit correct replication of the DNA during the cell's reproduction. However, UV radiation sterilization systems are often restricted because of their low penetration power.
8 ns Ho:YLF 3 micron laser
Authors: Kornev A.F. , Nikitichev A.A. , Pokrovskiy V.P. , Soms L.N. , Stoupnikov V.K.
Published: February 2023

Short pulse 3 µm laser is promising for medical applications, remote sensing techniques, and as the pump source for OPO operating in 5 µm spectral range. Unfortunately, low gain on the working transition of the most common diode pumped Er: YLF laser makes it difficult to obtain short pulses using Q-modulation techniques.
Phaselocking of multichannel lasers with a ring distributed individual channels by the unstable resonator with an internal W-axicon
Authors: Ageichik A.A. , Rezunkov Yu.A. , Stepanov V.V.
Published: February 2023

Multichannel laser systems which are designed according to the module principle are the most promising ones for development of the compact laser units. At present, the problems of multichannel laser designs and phaselocking of a number of individual resonators have been examined theoretically and experimentally mainly for continuously wave lasers, [1]. But, the compactness of high power laser device is poor. Besides, the requirements for the increase in output radiation power lead to further increase in the laser overall dimensions directly with the output power magnitude.
Nonlinear Operation of Hollow-Waveguide Slab Lasers with Gaussian Output Mirror
Authors: Witoński Piotr , Szczepański Pawel
Published: February 2023

Among different waveguide gas lasers. CO2 lasers have been extensively investigated theoretically as well as experimentally. Next, the use of slab waveguide structures in lasers were studied (see [1] and its references).
The Zig-Zag Resonator of the Coaxial High Power 6 kW CO2-Laser in Comparison to the Resonator With a Toroidal Mirror
Authors: Bohrer M. , Basalka H. , Le T. , Schuocker D.
Published: February 2023

A new high power CO2-laser with a coaxial resonator has been developed for industrial welding applications. The resonator is due to the philosophy of this product - to be cheap and reliable - very simple. A toroidal end mirror and a plane outcoupling window is used. The focus radius is limited to about 200 μm, which is typical for welding. An experimental setup of an alternative resonator has been developed. This resonator is a zig-zag resonator with eight or ten folding mirrors on each side. The beam has a gaussian mode. Therefore of course this laser can do cutting applications in high quality. Theoretical consideration are discussed in comparison to experimental results.
2D-Simulations of Tapered Amplifiers Comparison to Experimental Results
Authors: Chazan P. , Mikulla M. , Morgott S. , Wetzel A. , Kiefer R. , Walther M. , Braunstein J. , Weimann G.
Published: February 2023

The constant evolution of high power semiconductor laser sources has encouraged many groups to develop numerical methods for the calculation of the field intensity in the laser cavity. However, very few results have been reported about the comparison of experiment and simulations. In this contribution we present a 2D-model of tapered lasers and amplifiers, compare the calculations with experiment and derive some design tools for the optimization of tapered amplifiers and lasers.
Reliable high-power InGaAs/AlGaAs ridge waveguide laser diodes
Authors: Beister G. , Bugge F. , Erbert G. , Maege J. , Ressel P. , Sebastian J. , Thies A. , Wenzel H.
Published: February 2023

In application of RW laser diodes with monomode emission, like pumping sources for fibre amplifiers in optical communication systems, very high output powers are desirable. During the last years, remarkable success has been achieved to stabilize the facets of InGaAs/AlGaAs diodes, with emission wavelengths of about 1 μm, what allowed the production of highly reliable lasers. But along with these efforts, a lot of work has been done for further enhancement of device stability by replacing AlGaAs with Al-free materials. We show here, that the “pure" AlGaAs structures itself allows best performance at output powers of 300 mW.
Optimisation of flared semiconductor lasers and MOPAs
Authors: Kent A. , Skovgaard P. M. W. , McInerney J. G. , Moloney J. V. , Indik R. A. , Ning C. Z.
Published: February 2023

Semiconductor lasers which emit several watts into a single diffraction-limited lobe are extremely promising for a large range of applications such as free-space communication and pumping of fibre lasers and amplifiers. To date the most successful of these have been flared oscillators [1] and master oscillator-power amplifier (MOPA) [2] devices. Both classes of device are limited by filamentation, transverse beam instabilities and. in the case of the MOPA. reflection induced noise.
Polarization self-modulation in vertical-cavity surface-emitting lasers
Authors: Li Hua , Hohl Angela , Gavrielides Athanasios , Hou Hong , Choquette Kent D.
Published: February 2023

We experimentally and numerically investigated the characteristics of polarization self-modulation in vertical-cavity surface-emitting lasers (VCSELs). Polarization self-modulation was induced by using feedback from an external reflector with a quarter-wave plate to rotate the polarization direction by 90° [1]. We obtained a switching frequency of 9.18 GHz. The time traces clearly showed that the square-wave output for long cavity lengths changed to sinusoidal output for short cavity lengths indicating that the modulation characteristics are determined by a fundamental decay time. We also found that the external cavity system for short cavity lengths assumes eigenstates that are different from the free-running VCSEL eigenstates.
A new type of tunable solid-state far-infrared lasers
Authors: Mikhailov S. A.
Published: February 2023

A general analytic theory of voltage tunable solid-state far-infrared (FIR) amplifiers and generators, based on a current-driven instability of two-dimensional (2D) plasmons in a grating-coupled 2D electron system (ES) is presented.
Polarization and Transverse Mode Dynamics of Birefringent Index-guided Vertical Cavity Surface-Emitting Lasers
Authors: Valle A. , Martín-Regalado J. , Pesquera L. , Balle S. , Miguel M. San
Published: February 2023

In previous works [1] we numerically studied the polarization and transverse mode behavior of gain-guided Vertical Cavity Surface-Emitting Lasers (VCSELs) which can operate in several transverse modes corresponding to the same longitudinal mode. For this purpose, we used a generalized model which included (i) transverse effects, such as optical diffraction and carrier diffusion: (ii) the gain and dispersion spectra in a two-level Maxwell-Bloch approach: and (iii) the basic physical mechanisms of polarization dynamics such as saturable dispersion. VCSEL anisotropies and spin dynamics. Even though our results showed qualitative agreement with the experimental observations, it was not possible to identify completely the physical mechanisms governing the selection of the polarization state mediated by the transverse mode dynamics. The analysis of these mechanisms is difficult in gain guided VCSELs since transverse modes are not determined by the waveguide structure.
Femtosecond Autocorrelator Based On An AlGaInP Diode Laser
Authors: Bums D. , Lee S. T. , Dawson M. D. , Ferguson A. I.
Published: February 2023

We report on a sensitive autocorrelator for the 680-1300nm wavelength range, capable of sub-100fs resolution, based on two-photon-absorption (TPA) in an AlGaInP waveguide. The waveguide device is a low cost, commercially available, diode laser (SONY SLD 151V) which emitted at ~660nm under forward bias. We demonstrate that such lasers are eminently suitable for use as a stand-alone, processing-free, non-linear waveguide autocorrelator. Furthermore, the long interaction length due to the confinement in the waveguide results in high sensitivity. Autocorrelations of 100fs duration pulses have been achieved with single-beam incident powers as low as ~20μW. Similar AlGaAs-laser based detectors should be suitable for use in the 900nm-1.8μm range, and InGaAs(P) devices would extend the useful operating range to beyond 3μm. In principle, these detectors should be capable of operating down to ~1μW of incident power for ~100fs laser pulses.
Fast revision of spectral phase masks for femtosecond pulse shaping with neural network
Authors: Suzuki ML , Shiozawa M. , Takasago K. , Kannari F.
Published: February 2023

A complex shaped ultrashort waveform whose time-dependent amplitude and phase can be arbitrarily specified is generated from a single incident femtosecond pulse by Fourier synthesis. In principle, waveforms with arbitrary shapes can be formed if both spectral phase and amplitude are properly manipulated. However, when the reduction in energy that necessarily accompanies amplitude manipulation is undesired, spectral phase-only manipulation is required. A proper phase-only mask that generates a specified waveform can be found by using numerical optimization techniques, such as simulated annealing (SA) algorithm, similar to those widely used to design filters for spatial beam shaping. However, some femtosecond waveforms generated by phase-onlv filters are very sensitive to variations in the input spectrum. Therefore, one must always redesign the phase-only mask through some iterative algorithms when the input spectrum varies. The process takes relatively long time.
Attosecond pulse generation using high-order harmonics
Authors: Suda Akira , Le Kien Fam , Midorikawa Katsumi
Published: February 2023

Recent advances in femtosecond laser technology enable us to generate high-order harmonics in the extreme ultraviolet region. A number of studies have been performed with models which lead to the understanding of physics involved in the harmonic generation. It is expected that attosecond pulses are formed by superposition of equidistant frequencies from the high-order harmonics in a given spectral range.
Fluorescence lidar imaging of building monuments for remote assessment of algal and lichen growth
Authors: Raimondi V. , Cecchi G. , Pantani L. , Sundnér B. , Weibring P. , Johansson Th. , Edner H. , Svanberg S.
Published: February 2023

Remote fluorescence monitoring of the stone facades of historical monuments may provide valuable information in connection with damage assessment and restoration planning, since no scaffolding is needed and large areas can be covered in comparatively short times1. We report on first imaging measurements of this kind using a scanning fluorescence lidar system placed at about 50 m distance from the Lund Cathedral, the oldest part of which dates back to the 11th century.
Lidar Determination of the Mixing Layer Formation Delay in the Presence of a Fog
Authors: Tatarov Pl. Savov B. , Kaprielov B. , Kolev I.
Published: February 2023

The lidar investigation of dense atmospheric formations such as clouds and fogs is of great interest both for the fundamental and applied meteorology.
Integral Method of Multiposition Lidar Sounding of Aerosols and its Effectiveness
Authors: Perelman A. Ya. , Yegorov A. D.
Published: February 2023

The integral solutions of the lidar equation (Klett, 1981) commonly in use suffer from the fact of a priori assumed boundary values and relationship between backscattering and extinction coefficients. The integral method of the multiposition lidar sounding of the atmospheric aerosols was developed to exclude traditional systematic errors. The method is based on sounding of investigated atmospheric volume by lidar system transmitting pulses from different points in space and receiving the backscattering signals. It gives possibility to find a posteriori relationship between measured coefficients and the unknown boundary values using Bernulli solutions of lidar equation for beampaths segments forming polygons with common points. The effectiveness of the method is analysed for the ruby lidar system (Yegorov, 1996).
Organic Nonlinear Optical Materials
Authors: Bosshard Christian
Published: February 2023

Organic materials hold a large promise for second- and third-order nonlinear optical and fast electro-optic applications due to the large nonlinearities of the basic molecular units and the almost purely electronic origin of the nonlinearity. We here discuss the new development in this field with respect to molecules, polymers, and molecular crystals.
Time-resolved analysis of laserinduced birefringence in side-chain azobenzene polyesters
Authors: Hegelich M. , Hildebrandt R. , Keller H.-M. , Marowsky G. , Hvilsted S.
Published: February 2023

In certain types of azobenzen polyesters birefringence can be induced by irradiation with intense light of defined polarisation [1]. The induced birefringence is permanent but reversible. It is permanent in a sense that it remains stable when the pump laser is turned off and all short term relaxations ceased. The oldest sample holds its birefringence for more than five years. The direction of the birefringence can be influenced by the polarisation of the pump beam. That offers the possibility of erasing an already written value of birefringence by choosing the polarisation orthogonal to the original one.
Oxide-confined high-performance resonant-cavity light-emitting diode grown by solid source molecular beam epitaxy
Authors: Köngäs J. , Toivonen M. , Orsila S. , Savolainen P. , Pessa M.
Published: February 2023

A novel conception of light-emitting diodes, namely resonant-cavity light-emitting diode, has been proved to have several improvements over conventional LED’s including better spectral purity and enhanced output intensity [1]. However, the fabrication process remains comparable to that of a conventional LED. This makes an RCLED a competitive challenger for a vertical-cavity surface-emitting laser (VCSEL) for various applications in local area networking, optical computing measurement systems and densely packed displays.
Photonic crystal microcavity enhanced LEDs
Authors: Krauss Thomas F. , Boroditsky Mikhail , Coccioli Roberto , Painter Oskar , Scherer Axel , Yablonovitch Eli
Published: February 2023

One of the main motivations of pursuing research into photonic crystals is to modify the spontaneous emission rate in active material. In particular, the aim is to a) increase the extraction efficiency in LEDs, which is typically around 3-5% in commercial devices and b) to decrease the spontaneous emission lifetime, which is currently in the ns-regime, in order to enable high speed modulation. These goals can be achieved by suppressing the undesired electromagnetic modes into which the emitter can radiate, and by, concurrently, enhancing the desired modes [1].
The Characterisation of a Diesel Spray using Combined Laser Induced Fluorescence and Laser Sheet Dropsizing
Authors: Lockett R.D. , Richter J. , Greenhalgh D A
Published: February 2023

Combined planar Mie scattering and laser induced fluorescence (LIF) obtained from a spray seeded with a fluorescent agent permits droplet sizing, and is termed Laser Sheet Dropsizing or LSD [1]. This technique has enabled the characterisation of the spray in terms of the relative drop size distribution, the relative drop number density, and the relative liquid volume fraction.
Singlemode and Multimode Taper Optical Fibre Devices: Modelling, Testing and Fabrication
Authors: Moar P.N. , Katsifolis J. , Cahill L. W. , Huntington S.T. , Nugent K.A. , Roberts A. , Love J. D.
Published: February 2023

The evanescent field intensity outside a fibre can be increased several orders of magnitude by tapering it. Several tapered optical fibre based evanescent field devices have been reported in the literature. Cambridge University, UK, reported work on miniature dye lasers using a tapered fibre in a loop arrangement; but more importantly, a tapered single mode fibre bent into a small loop. This latter tapered device was used as an imunoassay for cholera antitoxin immunoglobulins and was based on fluorescence spectroscopy. The Naval Research Laboratories, USA, have reported on a MM tapered fibre which is chemically tapered to a point and can be used as a fluorescence based biosensor.
A New Method for Generation of a Variety of Narrow-Band Lines of High-Power Radiation in the UV Spectrum Region
Authors: Kachinsky A.V. , Ermakov A.V. , Orlovich V.A.
Published: February 2023

The progress established over the last decade in creation of UV radiation sources and highly sensitive multichannel detectors made it possible to successfully conduct the experiments in UV Raman spectroscopy with application to fundamental and applied studies in biology and material science. Among these are studies of the protein structure and dynamics along with diamond film growth. In these experiments, CW or pulsed UV radiation sources are normally used. Argon-and Crypton-ion CW frequency-doubled lasers. Nd:YAG pulsed lasers with harmonic generators and non-linear optical converters, based on stimulated Raman scattering (SRS) in gases, allow generation of radiation at a limited number of wavelengths, most of which lie in the λ ≥ 230 nm region. Dye-lasers excited with the second harmonic radiation of Nd:YAG- and XeCl-lasers allow continuously-tunable radiation to be generated in the λ ≥ 200 nm region. These laser systems, however, are very complicated.
Superbroadband laser for near IR, visible and UV spectral regions
Authors: Zverev Petr G. , Fedorov Vladimir V. , Basiev Tasoltan T.
Published: February 2023

In this report we discuss principles of recently developed superbroadband laser (SBL) oscillation and namely with
LiF:F
2
−
 and LiF:F
2
+
color center crystalline active element [1]. SBL optical scheme provides three types of laser oscillation spectrum: simultaneous superbroadband; multi-frequency or single-line tunable at the fundamental wavelength in the near IR from 850 to 1250 nm wavelength. The oscillation was realized due to a new laser cavity configuration [2]. The main idea of SBL operation consists in the independent oscillation of different parts of the active element with certain wavelengths from the amplification band of the active medium. The near IR output radiation of SBL has a spatially spread "rainbow'' spectra.
Synthesis and Spectroscopic Investigations of Yb3+-Er3+-Codoped LaLiP4O12 Glasses Relevant for Laser Applications.
Authors: Obaton A-F. , Bernard J. , Parent C. , Le Flem G. , Labbé C. , Le Boulanger P. , Boulon G.
Published: February 2023

We are involved in Yb3+-Er3+-codoped phosphate glass research for eye-safe laser source near 1535 nm, wavelength corresponding to the 4I13/2→4I15/2 Er3+ transition [1]. Undoped and doped glasses of the composition La2O3-Li2O-P2O5, with LaLiP4O12 formula, have been synthesised.
DPSSL with 2D Intracavity Beam Scanning Using Liquid Crystal Spatial Light Modulators.
Authors: Berenberg V. , Kornev A. , Onokhov A. , Pokrovskiy V. , Soms L. , Stoupnikov V.
Published: February 2023

The laser beam spatial distribution control can be obtained by the placing a Spatial Light Modulator (SLM) inside a special laser cavity. The opened pixels of the SLM determine the generating modes configuration (such SLM can be called "driven mirror"). The earlier works [1,2] has shown the possibility to obtain output energy level of solid-state scanning laser of several Joules on Q-switch operation, and high speed of scanning. At the same time, 2D random-addressing of laser beam by the single computer-driven SLM unit was the problem unsolved.
Inter Configuration Excited-State Absorption of Nd3+-Doped Fluoride Crystals
Authors: Guy S. , Guyot Y. , Joubert M. F.
Published: February 2023

The search for tunable blue-UV solid-state lasers has led to the recognition that 4fn-1 5d to 4P transitions of rare earth ions can potentially be useful for these types of laser systems. Such laser actions has been observed with Ce3+ or Nd3+-doped fluoride crystals. Nevertheless, these lasers suffer from solarization mechanisms which has been found to involve two-photon creation of color centers (via the 4fn →4fn-15d → conduction band pathway). One way to overpass this problem is a stepwise multiphoton excitation of 4fn-15d states with photons of low energy.