bluuebunny/crossref_metadata_2025 huggingface dataset:
All Solid State Blue Room-temperature Thulium-doped Upconversion Fibre Laser
Authors: Barber P. R. , Mackechnie C. J. , Lauder R. D. T. , Pask H. M. , Tropper A. C. , Hanna D. C. , Butterworth S. D. , McCarthy M. J. , Archambault J.-L. , Reekie L.
Published: February 2023

Following the report by Grubb [1] we describe an all solid state, single wavelength pumped, cw, room temperature, upconversion laser which has operated in the blue between 475 nm and 483 nm or in the near infrared at 778 nm.
Guided-Wave Distributed Bragg Reflectors With 0.7-μm Period Fabricated By Ion-Exchange in KTP
Authors: Risk W. P. , Lau S. D. , McCord M. A.
Published: February 2023

There is currently much interest in blue light sources based on quasi-phasematched frequency doubling of semiconductor diode lasers using periodically-poled nonlinear waveguides.
Demonstration of artificially structured tuning curves and enhanced acceptance bandwidths for quasi-phasematched frequency conversion in LiNbO3 waveguides
Authors: Bortz M. L. , Fujimura M. , Fejer M. M.
Published: February 2023

Quasi-phasematched second harmonic generation (QPM-SHG) in periodically poled LiNbO3, LiTaO3, and KTP waveguides is an attractive technique for the generation of short wavelength radiation from infrared laser diodes.
Structural Characterization of Rb+ Exchanged KTiOPO4 by Micro-Raman Spectroscopy
Authors: Tuschel David D. , Paz-Pujalt Gustavo R. , Risk William P.
Published: February 2023

Partial ion exchange of the alkali cation in single-crystal transition metal oxides that have a high nonlinear susceptibility is a convenient way of fabricating waveguides for second harmonic generation.1-3
Dopant induced birefringence tuning of KTiOPO4 for short wavelength frequency conversion.
Authors: Cheng L. K. , Cheng L. T. , Harlow R. L. , Bierlein J. D.
Published: February 2023

The excellent phase matching properties of KTiOPO4 (KTP), such as its high nonlinearity, broad temperature tolerance and large angular bandwidth have make KTP the preferred material for frequency doubling 1 μm lasers.
KTP and KTA Quadratic Non-Linearities
Authors: Boulanger B. , Feve J. P. , Marnier G. , Menaert B. , Cabirol X. , Villeval P. , Bonnin C.
Published: February 2023

KTP has five independent coefficients of the second order electric susceptibility tensor χ(2) (2ω = ω + ω) in the optical frame : χ15, χ24, χ31,χ32 and χ33.
Self-Frequency Doubling in Nd,Sc2O3:LiNbO3 Laser Crystal
Authors: Yamamoto Joyce K. , Sugimoto A. , Yamagishi K.
Published: February 2023

Nd doping of LiNbO3 combines the efficient laser oscillation of Nd with the strong linear or nonlinear optical properties of the host material.
Epitaxial LiNbO3 thin films grown on A12O3 by rf-sputtering
Authors: ARMANI-LEPLINGARD Florence , KINGSTON John J. , FORK David K.
Published: February 2023

Thin film technology is very attractive since it can allow integration of optical devices on the same substrate.
Generation of blue light by using potassium lithium niobate crystal
Authors: Mori Yusuke , Obana Takahiro , Sasaki Takatomo , Ohnishi Norio , Fukuda Tsuguo , Tanaka Hiroyuki
Published: February 2023

Potential application of a compact blue laser includes reprographics to data strage, biomedical diagnostics and so on.
Preparation of Gallium Nitride Epitaxial Films by Use of Low Energy Ion Beam Deposition
Authors: Fuguang Qin , Zhizhang Ren , Zhenyu Yao , Zhikai Liu , Dading Huang , Zhanguo Wang
Published: February 2023

Gallium nitride (GaN) is a direct transition type semiconductor with a band gap of 3.39 eV at room temperature, and thus has a potential for application to some novel optoelectronic devices working in the wave band from blue to ultraviolet.
A Frequency-doubled Diode Laser at 486 nm
Authors: Laurell F
Published: February 2023

Blue and green solid-state lasers are expected to replace gas lasers in certain low-power applications when a reliable technology is available.
Generation of violet-blue light by SHG of infrared laser diode in New Organic crystal -MHBA
Authors: Jiang M. H. , Yuan D. R. , Zhang N. , Tao X. T. , Xu D.
Published: February 2023

As a compact solid-state coherent source operating from the near UV to the green regions of the spectrum , laser diode-based second-harmonic generation (SHG) device hold much promise for use in optical storage and laser printer devices.
SHG of Green, Blue and Violet Light in LN Optical Superlattices
Authors: Ming N.-B. , Lu Y.-L.
Published: February 2023

It has been demonstrated that the enhancement of SHG can be realized by QPM1 in an Optical superlattice of LiNbO3 crystal, a LN single crystal with periodic laminar ferroelectric domains2,3, and the blue light were obtained by this method4,5.
0.6 W, Stable, Single-Frequency, Green Laser
Authors: Nightingale J. L. , Johnson J.K.
Published: February 2023

Intracavity-frequency-doubled, diode-pumped lasers are attractive sources of visible light.
KTiOPO4 blue laser using segmented waveguide structures
Authors: Bierlein J. D. , Roelofs M. G. , Brown J. B. , Tohma Teruo , Okamoto Sota
Published: February 2023

Several approaches are being evaluated for developing compact blue laser sources that can be used for optical storage, medical diagnostic, printing, and other applications.
Phase-unifying unstable resonators for excimer lasers
Authors: Fiori D. , Giuri C. , Perrone M. R. , Piegari A. , Scaglione S.
Published: February 2023

For some years now phase-unifying (PU) mirrors have been proposed as an alternative to graded reflectivity mirrors to improve the laser output beam quality.1,2 These mirrors can also have the advantage of a simpler fabrication. The PU mirrors that exhibit a stepwise reflectivity profile along the radius are made by deposition of a proper coating on a substrate so that no phase variations are introduced in the reflected and transmitted beam. A properly shaped substrate (with stepwise groove) has been used in most cases to cancel out the phase difference between the two beams passing through the internal and external regions of the coupler.3 The same effect, however, can be achieved by the coating design without substrate machining.
A N-(4-nitrophenyl)-L prolinol (NPP) near-infrared optical parametric oscillator tuned by pump frequency
Authors: Josse D. , Khodja S. , Samuel I. D. W. , Zyss J.
Published: February 2023

Rapidly tunable coherent sources of near infrared radiation are required for high speed multichannel optical communication networks, photonic switching systems, and other applications. Optical parametric oscillators (OPOs) are promising in this context, and the use of the organic crystal N-(4-nitrophenyl)-L-prolinol (NPP)1 has enabled very low thresholds to be achieved.2,4
Efficient frequency conversion of cw mode-locked tunable ps pulses in the visible and near infrared spectral region
Authors: Socha U. , Hussong J. , Beigang R.
Published: February 2023

Generation of ultrashort light pulses tunable in the whole visible and infrared spectral region is of considerable interest for a wide range of applications. Nonlinear frequency mixing techniques are well suited to generate such ultrashort tunable light pulses with a high repetition rate in these wavelength ranges. In particular, second-harmonic, sum, and difference frequency generation allow for the generation of tunable light pulses in a wide wavelength range depending on the laser sources used. Femtosecond pulses, e.g., have been generated in the wavelength range from 1.3 μm to 1.6 μm by difference frequency mixing of the cw mode- locked radiation of a Nd:YAG laser and a dye laser.1,2 In this contribution we report on the generation of tunable picosecond pulses in the wavelength range from 620 nm to 680 nm, 725 nm to 900 nm, and 2.6 μm to 4 μm by frequency conversion processes between the cw mode-locked radiation of a NaCl:OH color center laser and a Nd:YAG laser which is also used as the pump source for the color center laser.
Tuning of picosecond synchronously pumped sodium vapour OPO
Authors: Vaičaitis V. , Piskarskas A.
Published: February 2023

The synchronous two-photon excitation of 3-D sodium level has been carried out using the output of KDP optical parametric oscillator (OPO), and second-harmonic of a pulsed Nd:YAG laser with passive mode-locking and negative intra cavity feedback. Nd:YAG laser with three-stage amplifier system was delivering 60-80 pulses with a total energy of 60-80 mJ at 1 Hz repetition rate. Two light beams were used for excitation of the 3-D sodium level: the one, which was the signal wave of the KDP OPO (the wavelength λp1 = 962 nm, spectral width Δνp1 = 2,5-3,5 cm-1, energy of the train of 30-35 pulses Ep1 = 0,1-0,4 mJ, pulse duration τp1 = 12-18 ps, and the peak intensity of collimated beam Ip, = 0,04-0,16 GW/cm2), and the second-harmonic of the fundamental beam (λp2 = 532 nm, Δνp2 = 0,8-0,9 cm-1, Ep2 = 10-20 mJ, τp2 = 15-20 ps, and Ip2 = 2-4 GW/cm2). The second-harmonic train was used for KDP OPO as well as for sodium OPO pumping. The length of nonlinear medium in sodium vapour cell was 15 cm. When sodium vapour density was 1013-1017cm-3, the four-photon parametric luminescence in the 589-nm (signal wave) and 820-nm (idler wave) regions was observed. To achieve the positive feedback for four-photon parametric gain the ring cavity, formed mainly by Al-coated mirrors, was used.
Photon avalanche upconversion: an alternative model
Authors: Maciel G. S. , Goines A. S. L. , Acioli L. H. , de Araújo Cid B.
Published: February 2023

The avalanche upconversion process in rare-earth doped crystals has been dis covered few years ago1 and has attracted much interest. The effect is characterized by a sudden decrease in transmission above a certain intensity, and the rise time of upconverted fluorescence is intensity dependent.
Measurement of femtosecond time delay in optical materials using type-11 parametric downconversion
Authors: Sergienko A. V. , Shih Y. H.
Published: February 2023

Correlated pairs of photons generated in nonlinear Type II spontaneous parametric downconversion can be used to develop a new approach for the measurement of time delay between orthogonally polarized wave packets with femtosecond time resolution. This technique does not require the use of sophisticated and expensive femtosecond laser sources.
High-efficiency multicolour Q-switched Nd3+:KGd(WO4)2 laser
Authors: Stankov K. A. , Marowsky G.
Published: February 2023

Recently a new neodymium-doped crystal, Nd3+:KGd(WO4)2 (or Nd:KGW), lasing at 1067 nm, was demonstrated to exhibit highly efficient operation.1 The host crystal structure allows high doping (3-8 atomic percentage) without concentration quenching. Thus, higher specific energies can be achieved as compared to Nd:YAG. The crystal possesses other attractive features like broader luminescence bandwidth (24 cm-1) (which is promising for subpicosecond pulse generation) and large Raman-scattering cross section allowing for simultaneous generation of Stokes-shifted lines.
The 2 micron cw oscillation due to sensitization of Tm3+ions luminescence by Cr4+ions in YAG:Tm3+,Cr4+,Ca2+crystal
Authors: Borodin N. I. , Okhrimchuk A. G. , Smolin D. V.
Published: February 2023

In Ref. 1 authors supported that a four-fold coordinated four-valent chromium ion

Cr

t

4
+

may be used as a sensitizer of luminescence of some rear-earth ions in YAG crystal, but no oscillation experiments had been performed. For the first time we report about laser action on the 3H4→ 3H6transition of Tm3+ion when it is excited due to energy transfer from

Cr

t

4
+

ions.
Graded-phase mirror resonators
Authors: Paré C. , Bélanger P.-A.
Published: February 2023

Optical resonators designed for low- to medium-gain lasers generally consist of "stable" cavities using spherical mirrors. The nearly ideal Gaussian fundamental mode profile of such resonators is advantageous in terms of beam quality and reduced diffraction losses. However, for laser applications requiring single transverse mode operation, the stable geometry presents a serious drawback in terms of energy efficiency. The small beamwaist of the confined fundamental mode exploits only a reduced fraction of the available gain section and the poor modal selectivity limits the degree of saturation that can be reached in the single mode regime. The idea of using aspherical mirrors (graded-phase mirrors GPMs) has been proposed in the early days of laser development. The objective was to increase the effective mode cross section by improving the uniformity of the fundamental mode. However, in absence of guidelines, those studies were made on a trial-and-error basis and the conclusions were far from exhaustive. The interest for aspherical mirrors was also refrained by limitations in technology.
Analysis of higher-order waveguide modes via frequency offset re-injection
Authors: Pearson G. N. , Harris M. , Hill C. A. , Vaughan J. M.
Published: February 2023

CO2 waveguide lasers are usually designed with a view to obtaining operation exclusively on the lowest order resonator mode (often closely similar to the fundamental EH11 waveguide mode). However, this is not always achieved in practice because of various factors including the complications resulting from the incorporation of several intracavity elements and mirror misalignments. Higher-order resonator modes may come above threshold resulting in the mode-beating behaviour often referred to as hooting? For applications requiring single-frequency operation, such as coherent lidar, this is undesirable.
Bandpass switching based on a nonlinear optical loop mirror and an in-fibre grating reflector
Authors: Kean P. N. , Pattison D. A. , Forysiak W. , Bennion I. , Doran N. J.
Published: February 2023

The potential of the nonlinear optical loop mirror (NOLM)1 as a device for all optical switching applications has already been demonstrated at multigigabit repetition rates. Self switching of optical pulses within the NOLM requires breaking the loop symmetry to enable the counter propagating pulses to acquire a differential π phase shift. This is achieved with either an asymmetric fused fibre coupler at the input1 or by the inclusion of an asymmetrically located gain or loss element within the loop.2,3 By introducing a frequency selective loss element, non linear switching may be confined to a narrow band of wavelengths or multiple wavelengths. This configuration may have applications in time-wavelength demultiplexing. We demonstrate this technique of bandpass switching in the soliton regime using a fibre-Bragg grating reflector as the wavelength dependent loss.
Low power all-optical switch in a passive InGaAsP multiple quantum well waveguide
Authors: Snow P. A. , Day I. E. , Penty R. V. , Jiang Z. , White I. H. , Davies D. A. O. , Fisher M. A. , Adams M. J.
Published: February 2023

In recent years there has been much interest in all-optical switching in nonlinear semi-conductor waveguides, because of their potential for high-speed switching. To date much of the published work on all optical switching at wavelengths around 1.55 μm has concentrated on utilising the nonresonant Kerr nonlinearity in GaAs/AlGaAs structures.1 Whilst these devices exhibit switching times of approximately 100 fs, they require peak optical powers of the order of a hundred watts to operate. This makes them unattractive for telecommunications applications due to the high powers required. We demonstrate here the use of the resonant bandfilling nonlinearity in an InGaAsP/InGaAsP Multiple Quantum Well (MQW) waveguide due to photo generated carriers to obtain switching at pulse powers, which can readily be obtained from an erbium amplified diode laser source. In order to produce gating a polarisation rotation gate was used, which relies on an asymmetry in the nonlinear refraction on the principle axes of the waveguide.2 It has recently been shown that this nonlinearity can have a relaxation time as low as 18 ps.3
Soliton switching using cascaded nonlinear optical loop mirrors
Authors: Pattison D. A. , Kean P. N. , Forysiak W. , Bennion I. , Doran N. J.
Published: February 2023

Ultrafast soliton switching using the nonlinear optical loop mirror (NOLM) has been demonstrated both theoretically and experimentally.1,2 In addition, it has been shown that device cascading leads to an overall sharpening of the switching char acteristic.3-5 To date, however, the effects of cascading NOLMs operating in the soliton regime have not been considered. For the first time, we experimentally demonstrate a NOLM with a multiple peaked switching characteristic and, by feeding the switched signal back through the device in a double-pass configuration, use the first two response maxima to generate an enhanced switching response. We verify that solitons switched through the cascade maintain their temporal and spectral integrity. Since the construction of all-optical switching systems requires sequences of simple devices combined to produce higher level functionality, our results further demonstrate that the NOLM is a suitable building block for more complex soliton based switching scheme.
Efficient all-optical switching in a nonlinear AlGaAs X-junction
Authors: Aitchison J. S. , Villeneuve A. , Krijnen G. , Stegeman G. I.
Published: February 2023

Recently there has been a considerable amount of interest in all-optical switching using semiconductor waveguides operated at a wavelength corresponding to the half band gap.1 In this spectral region there is an enhancement in the nonlinear refractive index coefficient, n2, and the detrimental effects of two-photon absorption are minimised. By proper choice of material parameters, devices can be designed to operate in the 1.55 μm, low-loss window.
Diode laser bar beam shaping technique
Authors: Clarkson W. A. , Neilson A. B. , Hanna D. C.
Published: February 2023

Due to their relative cheapness and wide commercial availability high-power di ode bars are becoming increasingly at tractive as pump sources for high-power solid-state lasers. Unfortunately, because of the highly elliptical output beam (~1 μm × 10 mm) and highly nondiffraction-limited nature of these devices, they cannot readily be focused into small, circular spots, which are suitable for efficient end-pumping of solid-state lasers. To date, many of the end-pumping schemes, which have been employed with diode bars, have either produced a rather large focused pump beam diameter (typically ~ 1mm),1,2 or have employed relatively complex resonator designs (e.g., the tightly-folded resonator).3
Coherent laser radar based on semiconductor laser technology
Authors: Renhorn Ingmar , Broberg Björn , Vilhelmsson Kennet
Published: February 2023

Range, Doppler, and vibration measurements are used in a variety of applications, both military and civilian. The rapid laser development has brought about an increasing diversity in technology. Eye safety, low observability, and cost have been driving forces. A preferred wavelength is 1.54 μm, a wavelength that can be obtained by several types of lasers, one of which is the semiconductor laser. Semiconductor technology can lead to small, robust, and reasonably priced systems. The technology is compatible with fiber optics, which brings about the possibility to use a distributed sensor system. A special case already being exploited is in the area of time domain reflectometry. Due to the limited peak power capability of semiconductor lasers, direct detecting systems based on this technology have been background limited and only reached a limited capability. By using coherent detection and frequency modulation, close to quantum limited systems can be achieved. Similar capability might be obtained in a direct detecting system but only by making use of very advanced filter techniques. The linewidth of DFB and DBR lasers is now narrow enough for many applications. The advancement of semiconductor laser technology has motivated us to develop a compact and versatile coherent FMCW semiconductor laser radar.
Performance optimisation of an e-beam sustained CO2 laser for spaceborne Doppler wind lidar
Authors: Wallace S. , Schwarzenberger P. M. , Miller A. W.
Published: February 2023

The European Space Agency's programme for development of an e-beam sustained CO2 laser for Spaceborne Doppler Wind Lidar1 includes the performance optimisation study reported here, which primarily addresses the efficiency requirement.
Theory of semiconductor microlasers
Authors: Koch S. W.
Published: February 2023

Summary not available.
Approximate solution of the whispering gallery modes and estimation of the spontaneous emission coupling factors for microdisk lasers
Authors: Chin Mee-Koy , Ho Seng-Tiong
Published: February 2023

The threshold current of a microcavity laser with low transparency current is dependent mainly on the spontaneous emission coupling factor, β, which is the spontaneous emission rate into the lasing mode divided by the total spontaneous emission rate. The spontaneous decay may be modeled as stimulated decay due to stochastic vacuum field fluctuations.1 The decay rate, γ, of a dipole due to a mode (either radiation mode or guided mode) depends on the spatial mode area and the modal density of states.1 To estimate the β value for a microdisk laser2 where exact solutions are difficult to obtain, a simple approximate method for solving the waveguide modes and the density of states is developed here.
Occupation of higher conduction and valence subbands by resonant tunneling in CaAs/AlAs superlattices
Authors: Klann R. , Grahn H. T. , Ploog K.
Published: February 2023

The nonthermal occupation of higher subbands in superlattices by sequential resonant tunneling can give rise to new light emitting devices in the far-infrared spectral region, e.g., by using optical intersubband transitions. In contrast to luminescence spectroscopy,1 where a homogeneously distributed electron-hole plasma is generated optically, in possible device applications the electrons and holes are injected by ohmic contacts and occupy states according to their vertical transport properties.2 Therefore, we have studied the occupation of higher subbands by resonant tunneling in undoped GaAs/AlAs-superlattices (21-nm GaAs, 2.2-nm AlAs, 40 periods) via electroluminescence (EL) spectroscopy at T = 5 K.
Carrier capture and escape times in ln0.35Ga0.65As/GaAs multiple quantum well lasers determined from high-frequency impedance and modulation response measurements
Authors: Esquivias I. , Weisser S. , Tasker P. J. , Ralston J. D. , Rosenzweig J. , Romero B.
Published: February 2023

Although several models have been proposed to account for the influence of carrier transport, capture, and re-emission on the high-speed properties of multiple quantum well (MQW) lasers,1,2 very little experimental work has been carried out to directly determine the effective capture time into the QW's, τcap and the escape time out of the QW's, τesc. In the present work we utilize for the first time high-frequency impedance and modulation response measurements3 to evaluate τcap and τesc for In0.35Ga0.65As/GaAs MQW lasers with record 30 GHz modulation bandwidth.4
Room temperature green continuous wave Er3+:LiYF4 laser pumped by 810-nm Ti:sapphire radiation
Authors: Heine F. , Heumann E. , Danger T. , Schweizer T. , Koetke J. , Huber G. , Chai B.
Published: February 2023

Upconversion pumped visible solid-state lasers could be an interesting alternative to frequency-doubled infrared lasers or visible laser diodes in high-density data storage applications.
Orange, red, and deep-red flashlamp- pumped Pr3+:LiYF4 laser
Authors: Eichler H. J. , Liu B. , Meindl P. , Lu Zukang , Kaminskii A. A.
Published: February 2023

Praseodymium ions (Pr3+) exhibit very rich fluorescence radiation in the visible range.1 However, applications of flash-lamp-pumped Pr3+ lasers were restricted by the low slope efficiency, which results mainly from the narrow spectral range of Pr3+ absorption due to only three-four narrow lines in the spectral range of 420–480 nm.2,3
Art conservation studies by excimer laser
Authors: Hontzopoulos E. , Fotakis C. , Doulgeridis M.
Published: February 2023

Excimer lasers have been employed in a variety of diverse surface cleaning and surface modification applications. The present work investigates the application of excimer lasers for cleaning paintings of the ingrained layers of dirt from paintings that have accumulated from the surrounding atmosphere over the years, and for the removal of overpaintings.
Self-Q-switching of XeCI lasers by stimulated Brillouin scattering
Authors: Perrone M. R.
Published: February 2023

There has been considerable interest in the use of resonators with a phase-conjugate mirror to enhance the performance of pulsed lasers. Stimulated Brillouin scattering (SBS) is often chosen as the phase conjugation mechanism because of its relative simplicity and high efficiency. A further interesting feature of SBS mirrors used in phase-conjugate resonators (PCR) is represented by their capability of providing passive self-Q-switching because of their intensity-dependent reflectivity.
Stimulated Brillouin scattering techniques for phase-locked phase conjugation
Authors: Ridley K. D. , Scott A. M.
Published: February 2023

Phase-locked phase conjugation is the process of phase conjugating a number of laser beams whilst preserving their relative phases. Phase-locking is necessary when parallel laser amplifier channels are combined using phase conjugation, or when a depolarised beam is split into two orthogonal polarisations and phase conjugated.
Laser diagnostics of surface and film properties by surface acoustic wave pulses
Authors: Szabadi Martin , Kolomenski Alexandre , Hess Peter
Published: February 2023

Surface Acoustic Wave (SAW) pulses were excited by a frequency-trippled pulsed Nd:YAG laser of 200 ps pulse duration. The 355-nm radiation from this laser was focused onto the surface by a cylindrical three-lens-objective. In this way, a line focus of about 7 μm width and 7 mm length was formed. The total pulse energy in the line focus was typically 10 to 1000 μJ. This line focus could be scanned across the sample with a precision of better than 1 μm.
Sub-100 fs traveling wave parametric generator pumped by high repetition rate Ti:sapphire regenerative amplifier system
Authors: Siefert F. , Petrov V. , Noack F.
Published: February 2023

The traveling wave optical parametric generator (OPG) has been established now as a suitable tool for the generation of powerful tunable femtosecond pulses in the near infrared.1 All femtosecond OPGs reported so far have been pumped by amplified, colliding pulse mode-locked dye lasers operating at ≈10-Hz repetition rates and generated pulses comparable in duration with the pump pulse (of the order of 150 fs). They are characterized, however, by poor pulse-to-pulse reproducibility and bandwidths exceeding the Fourier limit, which reduces their applicability in time-resolved spectroscopy. The availability of commercial femtosecond Ti:sapphire amplifier systems operating at high repetition rates (1–10 kHz) offers the unique possibility of pumping an OPG with highly reproducible femtosecond pulses.
Low threshold 1.64 μm operation of a Yb,Er:YAG waveguide laser
Authors: Large A. C. , Hanna D. C. , Shepherd D. P. , Tropper A. C. , Warburton T. J. , Borrel C. , Ferrand B. , Rameix A. , Thony P. , Auzel F. , Meichenin D.
Published: February 2023

Er3+-doped Y3A15012 (YAG) is an interesting system with several useful laser transitions. Laser operation has previously been demonstrated on the 1.6 μm, 2.94 μm, and 561 nm shown in the level diagram of Fig. 1.1–3 Co-doping with Yb3+ allows these transitions to be pumped on the strong, diode compatible absorptions at 940 and 970 nm. Low-loss YAG waveguides grown by liquid-phase epitaxy have operated as low threshold lasers in Nd3+4 and Yb3+-doped systems. In the present work we have investigated the laser performance at 1.6 μm of Yb,Er codoped YAG epilayers grown on an undoped YAG substrate.
Advanced semiconductor laser structures for gas analysis spectroscopy
Authors: Sandström Lars , Höjer Svante , Ahlberg Henrik , Broberg Björn
Published: February 2023

Near infrared semiconductor lasers, operating in the 0.6–2.0-μm wave-length range, for gas monitoring applications is a fast-growing area. Semiconductor lasers have many advantages such as room temperature operation, several mW of output power in a single longitudinal mode, and compatibility with silica fibers and a variety of other fiber-optic components already developed. Commercially available semiconductor lasers are today optimized for the communication market, that in many cases favorize parameter settings of the laser structure in adverse of what is desired for spectroscopic use. Therefore, advanced multisection laser structures such as DFB (Distributed Feed Back) and DBR (Distributed Bragg Reflector) lasers are a necessity since each section can be controlled individually to a final performance opti­mized for spectroscopical need, such as large tunability, high SMSR (side mode suppression rate), and a low level of higher order harmonics of the modulation signal.
A novel concept for optical interconnects based on organic semiconductors and heterostructures
Authors: Ammermann Dirk , Rompf Christoph , Kowalsky Wolfgang
Published: February 2023

Modern high speed integrated circuits and computer boards for parallel distributed processing require a high degree of interconnectivity. Their performance, however, is often limited by the inherent characteristics of electrical interconnection: electromagnetic interference between parallel channels, signal dispersion and delays at high data rates, and low packing density. Optical interconnects offer an attractive alternative to overcome these limitations.
Photoassisted poling of spiropyrans in polymer films—experiments and theoretical model
Authors: Hosotte S. , Froc G. , Dumont M. , Atassi Y. , Nakatani K. , Delaire J. A.
Published: February 2023

Three years ago, we demonstrated Photo-Assisted Poling1,2 (PAP), a new optical technique for breaking the centrosymmetry of some dye-doped polymer films, in order to induce Second Harmonic Generation (SHG) and Electro-Optic (EO) properties. The first experiments have been performed with azobenzene derivatives, particularly Dispersed Red 1 (DR1), in which the photoassisted poling is due to the Trans-to-Cis photoisomerization (N=N double bond). When molecules relax back from the bent Cis shape to the linear Trans state, their orientation is modified: this process induces an anisotropic angular distribution of molecules, because of the anisotropy of the pumping light and a noncentrosymmetric distribution, if a DC electric field is applied during the optical pumping. In PMMA-DR1 copolymer films, PAP has produced large and stable χ(2).
Nonlinear optical properties and electroinduced effects on second harmonic generation in Si/SiO2 superlattices
Authors: Aktsipetrov O. A. , Fedyanin A. A. , Golovkina V. N. , Murzina T. V. , Keller O. , Pedersen K. , Zayats A. , van Hasselt K. , Rasing T.
Published: February 2023

Last year there was an increasing interest in the fabrication and the investigation of low-dimensional structures such as quantum dots, quantum wells, superlattices (SL), etc. The semiconductor superlattices demonstrated a lot of interesting optical and nonlinear optical properties associated with their periodical structure. In this report we present our results on second-order nonlinear optical properties of Si/SiO2 superlattices, the influence of the external DC electric field, as well as Si and SiO2 thicknesses on the optical second harmonic intensity in this type of SL.
Simultaneous generation of sum, difference, and harmonics of two laser frequencies by spread spectrum phase matching
Authors: Horowitz Moshe , Bekker Alexander , Fischer Baruch
Published: February 2023

Nonlinear parametric processes, that now seem to be the most promising means for providing laser light beams with very large tuning ranges, have a critical limiting factor due to the phase matching requirement. Violation of this requirement is possible when the interaction length is limited to very "thin" crystals. The common method to solve this problem is by using the crystal birefringence. This allows a limited degree of wavelength tunability by changing the angle of the beam propagation in the crystal. Another solution is quasi-phasematching by "artificial" spatial modulation of the optical nonlinearity, or the refractive index also restricts the phase matching to a specific input wavelength. In recent works1 we have demonstrated a new method for broadband second harmonic generation (SHG) by controllable spread spectrum quasi-phase matching. The broad spectrum of the domain grating period provided the broadband capability. We have also demonstrated second harmonic generation for prespecified discrete or continuous beam wavelengths by tailored quasi-phase matching.2
Experimental investigation of supermode output waveguide CO2 laser resonator
Authors: Xin Jian Guo , Zang Er Jun , Wei Guang Hui
Published: February 2023

In the recent few years, some researchers have paid a great interest in RF discharge excited waveguide array CO2 lasers for their advantages over single channel structure lasers. A variety of waveguide array coupling techniques and structures have been proposed and reported. In this paper, we shall present the results of experimental studies of a new type of optical waveguide resonator that is combined with an RF discharge excited large aspect ratio waveguide to produce a far field highly suppressed supermode output beam. This type of waveguide optical resonator laser has demonstrated the characteristics of a linear waveguide array CO2 laser. At near field, the intensity distribution of the output beam manifests itself as many horizontally lined separate beam spots; at far field, the intensity distribution of the output beam shows horizontally a highly spatially suppressed single peak. Experimental study has revealed that for the supermode beam, the surface curvature of the waveguide optical resonator mirrors plays a very important role, and as the length of the waveguide optical resonator varies, the far field intensity distribution of the output beam changes periodically. The experimental results have also shown that the aspect ratio of waveguide cross section has less influence on the output beam characteristics of this type of waveguide optical resonators.
Lifetime measurements in annealed proton exchanged Nd:LiTaO3 waveguide
Authors: Nouh S. , Baldi P. , de Micheli M. , Monnom G. , Ostrowsky D. B. , Lallier E. , Papuchon M.
Published: February 2023

Following the recent success in fabricating laser devices in rare-earth-doped lithium niobate,1 it appeared interesting to develop similar elements in rare-earth -doped lithium tantalate in view of this latter material's reputation for having a considerably higher optical damage threshold. Unfortunately, first attempt,2 using proton exchanged waveguides on Nd:LiTaO3 was not very successful due to a reduction of the 4F3/2 excited state lifetime of Nd3+. In order to understand this phenomena and improve the laser performance, we monitored the lifetime as a function of the proton concentration, which was varied by successive annealing.
Synthetic multilevel diffractive optical elements for beam shaping and harmonic separation applications in high power laser systems
Authors: Miller J. Michael , Blair Paul , Barton Ian M. , Taghizadeh Mohammad R. , Bett Thomas H. , Stevenson R. Martin
Published: February 2023

Diffractive optical elements offer many advantages over conventional optical elements in high power laser systems; e.g., focussing beam sampling and splitting elements.1 Typical benefits include the ability to perform multiple optical functions with one element, high laser damage thresholds,2 reduced nonlinear phase retardation and the possibility of mass production using VLSI fabrication techniques. Here, we present the design procedure and experimental results for a 16- level on-axis near-field Gaussian to flat-top generator with low fidelity and an harmonic separation filter for purging 3λ0 and 2λ 0 wavelengths from a laser beam to leave only the desired λ0.
Micro-regional temperature measurements of biological membranes irradiated by optical tweezers
Authors: Liu Y. , Cheng D. , Sonek G. J. , Berns M. W.
Published: February 2023

Single-point thermometry, or the measurement of localized temperature changes, is a key technique for characterizing the physical, chemical, and biological process at a specific biological site, especially for a medium that can be heated up by a highly focused laser beam. Herein, we report on the development of a technique for the nondestructive local temperature measurement of optically irradiated biological membranes, based on fluorescence from an environmentally sensitive dye1 in an organically engineered liposome.2 An optical multichannel analyzer (OMA) is combined with a microscope to measure spectral fluorescence (see Fig. 1) to offer a high temperature sensitivity, submicron spatial resolution, high speed, and large signal-to-noise (S/N) ratio. In addition, this technique is nondestructive. The most sensitive temperature regime for this measurement is in the vicinity of the phase transition temperature of the liposome, which depends on its membrane molecular structure. Using this technique the temperature in a micrometer region has been measured, with a 0.1°C sensitivity.
Microscopic correlation imaging through scattering media
Authors: Kempe M. , Rudolph W.
Published: February 2023

Optical imaging through scattering media with sub-mm spatial resolution using short light pulses and suitable correlation techniques has been proven successfully by several groups (see for example Refs. 1–4), with interesting application potentials in biology and medicine. The short light pulse (or broadband coherent light) illumination serves to separate the imaging signal from the scattered background. To achieve µm spatial resolution these techniques need to be combined with microscopic imaging. Here we describe a linear correlation technique that not only provides the gating but also spatial resolution similar to ordinary confocal imaging. The schematic diagram of the apparatus is shown in Fig. 1. Pulses from a fs Ti:sapphire laser (800 nm, 100 fs) are coupled into a Michelson interferometer that contains a (home-made) laser scanning microscope. The reference arm is terminated by a loudspeaker that is driven by a frequency of f = 2kHz, producing an oscillation amplitude of about 5µm. The fringe modulation (if both arms have the same length) is detected by a photodiode D1. The amplified and rectified signal is then sent to a lock-in amplifier operating at 2/. An improvement of the signal to noise ratio can be achieved by using a second detector D2 at the other output of the Michelson and processing the difference signal D1-D2.
Laser fourier holographic microscope and a problem of speckle-noise removal
Authors: Karpov Vladimir B.
Published: February 2023

Optical microscope (OM) is one of the human instruments that will hardly fall into oblivion in awhile. Nevertheless, it posseses the disadvantage of considerably limiting the obtainable volume of information about an investigated sample.
Hypocrellin (HA) probing of cardiovascular atherosclerotic deposits and cervical malignancies via laser induced fluorescence spectroscopy
Authors: Papazoglou T. G. , Liu W. Q. , Manolopoulos A.
Published: February 2023

Laser-induced fluorescence spectra were recorded during the exposure of normal, atherosclerotic cadaveric aortic tissue, and cervical biopsy samples taken during hysterectomy to He-Cd (442 nm) laser irradiation. Eleven abdominal aortic and femoral artery samples from two autopsies and three by-pass operations were obtained in an unfixed state within 12 hours of their excision. Similarly, twelve tissue samples from three hysterectomies were obtained within 3 hours from the operation. Following gross inspection, three aortic samples and nine cervical lesions were classified as normal and the rest as either samples of various degrees of atherosclerosis (fibrous, fatty plaque, aneuresmal thrombus, calcified plaque) or malignant lesion of the cervix and uterus. Simple algebraic algorithms, based on the relative intensity of two spectral regions (516–525 nm and 590–600 nm), implemented on the emission spectra were sufficient to discriminate between fibrous and aneuresmal tissue and normal aortic samples (Fig. 1). After treatment with Hypocrellin (10-3 M in CH2C12), the same semi-empirical algorithms were able to discriminate between normal and fatty-calcified samples, as well as normal and malignant cervical tissue (Fig. 2).
Synthetic discriminant filtering techniques for laser cutting process control
Authors: Huang M. Y. , Chatwin C. R. , Wang R. K.
Published: February 2023

Characteristic spark cone images are produced beneath the workpiece during reactive gas-assisted laser-cutting processes. Laser-cutting quality is controlled using robust optical pattern recognition and classification of the spark cone images. High irradiance fully formed spark cones are characteristic of a high quality dross-free cut; whereas, a sparse cone indicates a poor quality cut with dross attachment to the lower surface of the workpiece. It was found that by incorporating both the out-of-class image, sparse spark cone, and the in-class image, fully formed spark cone, into a Wiener filter construction, the discriminant ability of the imaging control system was significantly enhanced, the incorporation of three out-of-class images gave optimum performance. The Wiener filters formed from spark cone images, recorded when cutting different thickness materials, were integrated into a synthetic discriminant function (SDF) filter. When spark cone images from the laser cutting process were cross-correlated with the SDF, it gave a high output peak for a good quality cut, and a low output noise signal for a poor quality cut.1-5
Wide gap laser welding with filler powder
Authors: Ferravante L. , Fraschini P. L. , Mor G. P. , Balbi M. , Molinari O.
Published: February 2023

In laser welding one of the most critical factors is a tight fit of the seam joint, because any gap in the seam produces voids or undercuts in the finished weld.
Laser cutting of aluminium alloys
Authors: Dabezies B. , Alarçon C.
Published: February 2023

In the case of rail transportation, one of the great challenges for the future is to improve the mass capacity without increasing the weight of the vehicles. One of the solutions is to introduce, at the place of steel, aluminium alloys. In this case, the first step is to show the capability of the high productive cutting setup, such as lasers, to machine aluminium plates.
Absorption spectra of photosensitizers measured in vivo by time-resolved reflectance
Authors: Cubeddu R. , Musolino M. , Pifferi A. , Taroni P. , Valentini G. , Canti G.
Published: February 2023

The absorption properties of photosensitizers for the photodynamic therapy of tumors (PDT) may be significantly influenced by their interactions with the biological substrate, leading to an in vivo spectrum, which cannot be predicted on the basis of in vitro studies. Therefore, for the development of an optimized clinical protocol, it is fundamental to estimate the absorption spectrum in vivo non-invasively, thus determining the best irradiation wavelength. This measurement can be performed by means of time-resolved reflectance, which allows to evaluate both the absorption and the scattering coefficients, and therefore provides also information on the light penetration in tissues, useful to define the optimal light dose for therapeutical purposes.
Experimental and numerical investigations of two-dimensional "Antiresonant Reflecting Optical Waveguides'' (ARROWs) based on AlGaAs/GaAs
Authors: Freye Roland , Delonge Thomas , Bönsch Peter , Fouckhardt Henning
Published: February 2023

The device concept of a two-dimensional ARROW and its technological realization is reported. ARROWs belong to the class of leaky Bragg waveguides in integrated optoelectronics.1 Despite core sizes of dc = 5 µm quasi-monomode waveguiding is achieved by reflection at Bragg layers. These layers operate in antiresonance for the fundamental mode, i.e., due to its optical path length the attenuation coefficient is rather small (typically α < 0.5 dB/ cm) for this mode only compared to every other leaky mode (typically α > 20 dB/cm). The device exhibits antiresonant guiding in both cross sectional dimensions, so the ARROW fundamental mode profile is similar in shape and size to that of a monomode glass fiber. Hence, efficient ARROW based fiber-chip coupling can be achieved with coupling coefficients of η ≃ 95%. We used AlGaAs/ GaAs as an exemplary material system.
Embossed polymer waveguide devices
Authors: Harvey T. G. , Allen S. , Bone D. J. , Bone E. L. , Carter N. , Cinderey M. B. , Laidler D. , Quinn S. , Ryan T. G. , Summersgill P. , Thorne A. J. , Cush R. , Goodwin M. J. , Salik M. D. , Stewart W. J. , McRobbie G.
Published: February 2023

Recently there has been renewed interest in moulding and embossing of polymers as potentially cheap methods of mass producing passive waveguide devices.1,2 Manufacturing components with good optical performance by these methods requires careful control of the fabrication process and the use of materials with optimised properties. Ideally the materials should have low intrinsic optical loss at 1.3 and 1.55 micron, should be refractive index matched to silica, and should provide acceptable thermal stability. Also, they must be processible. We have synthesised deuterated and non-deuterated fluoromethacrylate resins, which satisfy these criteria. They have intrinsic losses of 0.1 dB/cm at 1.3 micron and 0.6 dB/ cm at 1.55 micron whilst their refractive index is 1.45 at both wavelengths. Furthermore, their reflective index can be tuned by changing the amount of fluorine in the resin formulation. We have produced single mode waveguide power splitters using this material by embossing.
Large-core, high-bandwidth polymer optical fiber and its application
Authors: Ishigure Takaaki , Nihei Eisuke , Koike Yasuhiro
Published: February 2023

For expanded data communication networks, silica-based single-mode (SM) optical fiber has been widely used especially for long haul communication because of its high transparency and high bandwidth. However, the small core diameter of the SM fiber such as 5-10 µm requires the accurate fiber coupling technology, and will significantly increase the total costs in the FTTH and Interconnection.
Single-mode monolithic ring laser with vertical grating coupler
Authors: van Roijen R. , Horikx J. J. L. , van der Heijden J. M. M. , van Dongen T. , Verbeek B. H. , van Stralen M. J. N.
Published: February 2023

Monolithic ring lasers in InP are well suited for application in integrated components in the telecommunication optical window. A number of methods for coupling light out of a ring have been reported,1-4 but often these methods are very demanding on technology. Wavelength selection and stability in monolithic ring lasers are also important issues.
Surface mode-coupling in GaAs/AlGaAs laser diodes—a new technique for a single mode laser
Authors: Köck A. , Gmachl C. , Gornik E. , Korte L. , Rosenberger M. , de Souza P. Lustoza
Published: February 2023

Single longitudinal mode laser diodes are of high interest for optical fiber transmission systems. Among the many types of single mode laser diode structures the distributed feedback (DFB) laser diode presently seems to be most promising.
Modelling of quantum-well second-order distributed Bragg reflector lasers
Authors: Bonnefont S. , Lozes-Dupuy F. , Dagens B. , Arguel P. , Leymarie H. , Martinot H.
Published: February 2023

Distributed Bragg reflector (DBR) semiconductor lasers have received considerable attention because of their superior operating characteristics and their suitability for integration into a surface-emitting or edge-emitting device to provide a coherent and high-power light source.1,2 Recent reports have demonstrated that a DBR laser is a key component in mono-lithically integrated master oscillator power amplifiers (M-MOPAs) and mono-lithically integrated active grating master oscillator power amplifiers (MAG-MO-PAs). These devices have shown considerable promise as efficient sources for a variety of applications including freespace optical communication, remote sensing, optical printers, and nonlinear frequency conversion.