bluuebunny/crossref_metadata_2025 huggingface dataset:
Compact Nonlinear Wavelength Conversion Devices with Distributed Bragg Reflectors on Periodically Poled LiNbO3
Authors: Hsu Chih-Wei , Yang C. C.
Published: February 2023

Typically, placing a quasi-phase matched nonlinear optics crystal in a resonance cavity, such as the cases of optical parametric oscillator (OPO) and second-harmonic oscillator (SHO), can lead to efficient wavelength conversion. With the end faces well polished and HR-coated, compact devices can be achieved. Because we have successfully developed a simple laser ablation method for grating formation on LiNbO3, here we propose an alternative of making compact OPO’s or SHO’s by using distributed Bragg reflectors (DBR’s). Such a device has the advantage of smaller output spectral widths due to the use of gratings. In this paper, we present the results of our numerical simulations for DBR SHO’s and OPO’s based on periodically poled LiNbO3 (PPLN). The basic device design is to first fabricate a channel waveguide on a PPLN crystal and then make two gratings at the ends of the waveguide. The longer (shorter) grating serves as the end mirror (output coupler). The fundamental (pump) for a SHO (OPO) is incident from the side of the end mirror. The grating period is designed for the Bragg reflection and hence oscillation of the second harmonic (signal) of a SHO (OPO). We have found that the numerical results of the output of such a device depended on the cavity dimensions, pump power level and phase mismatch parameter of the grating. Therefore, it is expected that for fixed cavity dimensions and pump power, the device should provide the output with the optimum phase mismatch parameter. Figure 1 (filled circles) shows the second harmonic output vs. the normalized phase mismatch parameter (δ/κ) of a DBR SHO when the fundamental input is 10 KW/cm2. There are two peak values when the normalized mismatch parameters are 0.225 and 0.668. For comparison, the dashed line shows the result when the gratings are removed (single pass second-harmonic generation). Note that with the DBR’s, the output can be enhanced by at least 13 dB.
Efficient tunable red-yellow solid state laser based on second harmonic generation of Cr:forsterite in KTP
Authors: Giffin Shirin M , McKinnie Iain T
Published: February 2023

A new approach to developing efficient tunable visible solid state lasers is demonstrated. Broadband tunability in the yellow-red region is obtained using intra-cavity second harmonic generation of gain-switched Cr:forstente lasers in KTP. Tunable lasers in this region are attractive for remote sensing, dermatology and isotope separation. The devices described here provide an alternative to solid state dye lasers and OPOs which are limited by short operating lifetimes and strict spatio-temporal pump laser tolerances, respectively. The 1150-1350 nm wavelength range of Cr:forsterite is well-suited for frequency-doubling to the red-yellow region. Second harmonic generation of femtosecond forsterite pulses has previously been reported1 but, to our knowledge, characterisation of efficient frequency doubling has not been carried out for gain switched pulses.
All-Solid-State Deep-Ultraviolet Continuous-Wave Coherent Light Source with External Enhancement Cavities
Authors: Matsubara K. , Tanaka U. , Imajo H. , Hayasaka K. , Ohmukai R. , Watanabe M. , Urabe S.
Published: February 2023

A compact tunable ultraviolet coherent light source based on diode lasers would have wide application. However, there are only a few reports on that at wavelength below 250 nm. We have generated continuous-wave coherent light at 214.5 nm by frequency-quadrupling an output of a high-power diode laser system through two frequency doubling stages [1]. Our motivation to this subject is a development of an all-solid-state light source for laser cooling of Cd+ ions, which we propose as a candidate for a future frequency standard [2].
Using the ultraviolet laser beam for control of radio-protective effect during the action of hard ionizing radiation on DNA macromolecules
Authors: Vysotskii V.I. , Pinchuk A.A. , Kornilova A.A. , Samoylenko I.I.
Published: February 2023

Combined effects of UV-laser radiation and hard ionizing radiation (neutrons, X(γ)-quantum) on depolymerisation, repairing and stability of DNA are studied. The investigations have been aimed at determining die conditions under which double breakages of DNA macromolecules chains (owing to detrimental action of hard radiation) become self-eliminable when the UV-laser radiation helps to recover the viability of the biosystem. Strict quantum-electrodynamic considerations suggest that die forces of interaction between the two nucleotides on die opposite sites of a break are totally under the control of the width of the break L as well as of dispersion features of dielectric permeabilities εi(ω) of die nucleotides (Adenine, Thymine, Cytosine, Guanine) and intermolecular salt-aqueous medium ε3(ω) through all the range of frequencies.
Spectral and lasing properties of Er3+: YVO4 crystals
Authors: Zhang Z.G. , Wang J G. , Xu J.R. , Fu P.M. , Eichler H.J. , Liu B. , Taeuber U. , Diening A. , Huber G. , Yan X. L. , Wu X. , Jiang Y.D.
Published: February 2023

Er3+-doped cry stals, glasses and fibers exhibit fluorescence and laser activity in a broad spectral range from infrared down to the ultraviolet owing to the complex energy level schemes of Er3+-ions. In recent years extensive investigations on Er3+-doped fluorides [1-2] and oxides [3] were carried out to find out appropriate laser materials for 3 µm and visible emissions for diverse applications. Spectral properties and laser behavior of new Er3+-doped host materials are especially interesting for comparison.
Determination of the thermal lens in laser materials by measuring the fluorescence distributions
Authors: Siegel Ch. , Graf Th. , Balmer J.E. , Weber H.P.
Published: February 2023

The performance of a solid-state laser is strongly influenced by thermally induced distortions (temperature-and strain-induced variation of the refractive index and curvature of the end face). All these effects contribute to the thermal lensing in the rod. To measure the dioptric power, we make use of the cylindrical symmetry of the pump and rod geometry and the optical isotropy of the crystal. During laser operation the stimulated emission reduces the amount of spontaneous emission at the location of the laser mode. With a CCD camera the distribution during laser operation and without laser emission is recorded through a planar facet along the rod axis. Under presumption of cylindrical symmetry the three-dimensional distributions can be reconstructed with a numerical code. By comparing these two distributions we developed a method to directly determine the radius of the fundamental mode in the crystal (Fig. 1). Using the propagation matrix method, the dependence of the mode radius w on the pump power P can be derived [ref 1], w(P) contains a material constant f*. the specific focal length, which can be found by comparing the calculated mode radius in the crystal with the mode radius determined in the experiment. The measurements were performed with a single end-pumped Nd:YAG rod and f* was fond to be 4.03 m-W/mm2 (Fig 2)
Time evolution of the beam quality factor in Gaussian cavities of different length
Authors: Perrone M.R. , Diso D.
Published: February 2023

The improvement of the optical quality of the laser radiation delivered by high-power excimers is strongly demanded to achieve a greater utilization of their laser energy. Moreover, in applications in which excimers are used for precision drilling, cutting and writing diffractive optical elements, laser beams of low divergence and with a quite uniform intensity profile are needed. Recently, plane-parallel cavities with a Gaussian-reflectivity-profile mirror as full reflector have been applied to a XeCl laser and it has been shown that excimer lasers fitted with plane-parallel Gaussian cavities deliver laser beams with quite uniform intensity profiles and with beam-quality-factor M2 more than 50% smaller than that of laser beams delivered by plane-parallel cavities using conventional high reflectivity mirrors as full reflectors [1].
Laser resonators with the given output by using adaptive mirrors
Authors: Cherezova T.Yu. , Chesnokov S.S. , Kaptsov L.N. , Kudryashov A.V.
Published: February 2023

The problem of formation of the given intensity distribution at the surface being treated has become particularly topical because of the widespread use of lasers in technological processes and medicine. This problem was solved previously by use of compensators, kinoforms, spatial filters, etc. However these optical elements were developed for beams with the given structure (mostly Gaussian). Varying the illumination conditions, the efficiency of such elements deteriorates appreciably. Another way to solve this problem is to use graded reflectivity mirrors [1] inside laser cavity. This appears to be the optimum solution for the lasers with an unstable geometrv. But for stable ones with small gain the intrinsic loss of a graded reflectivity mirror is Too high. Then it was suggested to extend the same fabrication technology for stable lasers and to develop graded-phase mirrors [2], But the shortcoming of such correctors is the narrow sphere of their application: every change of laser parameters needs its own unique graded phase mirror.
Q-Switch behaviour of different solid state laser hosts
Authors: Falter S. , Schröder O. , Du K.-M. , Loosen P. , Poprawe R.
Published: February 2023

From experiments with Q-switched solid state lasers it is known that a typical repetition rate exists, being characteristical for the employed laser crystal. If the actual repetition rate is below this value the pulsewidth τ is small but the average power

P
¯

decreases, while for a higher repetition rate the pulses become broad and

P
¯

increases. The first case is preferable in order to achieve high peak powers, and crystals with a long fluorecence lifetime like Nd:YLF are the preferable choice. Nevertheless, for applications like marking or drilling the repetition rate is of high interest because it increases the processing speed. Investigating the three classical crystals Nd:YAG, Nd:YVO4, and Nd:YLF under comparable circumstances we found, that in a plot of the ratio

P
¯

/
τ

vs. the repetition rate v a maximum occurs. This maximum corresponds to the repetition rate at which the conversion efficiency of the external frequency doubling process becomes maximal and processing effect on metallic surfaces stays considerable. Upon the rate-equation based Q-Switch theory described in References (1,2) we are able to explain the experimental laser-behaviour illustrated in figure 1. Furthermore, predictions for other four-level solid-state laser hosts can be made and conclusions concerning the crystal quality can be drawn.
Improvement of a short pulse KrF excimer laser by an unstable resonator with super-Gaussian mirror
Authors: Pätzold H.-J. , Woggon S. , Grunwald R. , Ehlert R. , Griebner U.
Published: February 2023

Short pulse excimer lasers are an ideal tool for material processing. The poor beam quality results in large focus diameters and prevents a cutting directly with the focused laser beam. An improvement in beam quality can be obtained by replacing the plane-parallel resonator by an unstable resonator with an output coupler of super-Gaussian reflectivity profile. For such type of lasers, a low number of round trips (n=2) and geometrical limitations in cavity magnification M (max. M=5) caused by the discharge chamber and electrode dimensions are significant. For this conditions, beam parameters and output energy for different resonator types have been calculated using the beam propagation method. The beam quality was characterised by the M2-factor on the basis of the second moment of the energy density distribution. For the plane-parallel cavity, the variation of parameters like cavity length and diameter of intra-cavity apertures showed a remarkable correspondence between simulation and experimental behaviour for the M2-factor and output energy in the vertical beam direction. In horizontal beam direction, an additional introduction of diffuse scattering at the electrodes was necessary to complete the model. The temporal gain behaviour has the strongest influence on the correlation between theory and experiment and its exact measurement was quite difficult in our case.
Strong optical asymmetry of unequal-reflectivity mirrors interference wedge as a base of a new technique for noise-free coupling of tunable laser oscillator and amplifier
Authors: Stoykova E. , Nenchev M.
Published: February 2023

A strong spectrally dependent optical asymmetry of unequal-reflectivity mirrors interference wedge (IW) was recently reported (theory, experiment). Deriving a set of equations for laser illumination with beam diameters of 0.2-0.6 mm, we demonstrated a qualitatively different structure of the resonant reflected intensity for both directions of beam falling [1]. Reflected beam profiles were calculated on the IW surface. First, in the present report we model the interference profiles at a distance from the IW using diffraction integral and the complex amplitude distribution on the wedge surface. We confirm that far from resonance both reflected beams propagate in accordance with Snell’s law. At resonance, the main part of the beam (more than 70% at R1~ 70-80% and R2~96-99%) reflected from the lower-reflectivity side of the wedge propagates in direction different from the off-resonant beam direction.
Numerical Analysis of Laser Beam Width and Beam Quality of Q-switched Lasers Using Different Definitions of the Beam Width
Authors: Ajer Halvor
Published: February 2023

With the increasing number of laser applications, there is a need for unambiguous and simple methods for measurement of laser beam parameters such as beam width and beam quality. There have been numerous approaches to this, see e.g. [1], which all have their limitations, depending on the application of the laser beam. Even further complications arise when trying to characterize the time-varying output from pulsed lasers, in which case the propagation properties of the beam will in general vary throughout the pulse.
Design of Variable Reflectivity Output Coupler for High Power CO2 Lasers
Authors: Bartels Heike , Habich Uwe , Poprawe Reinhart
Published: February 2023

In order to increase the laser power of CO2 lasers the active volume has to be enlarged. For CO2 lasers there are two possibilities: to increase either the resonator length or the tube diameter. A larger tube diameter means a higher Fresnel number and the laser will be most likely operated with an unstable resonator configuration, which extracts a beam with higher beam quality than a multimode stable resonator. Increasing the resonator length while the diameter remains constant leads to a smaller Fresnel number and a stable resonator configuration becomes reasonable. However, in both cases diffraction effects will be observed due to the limiting apertures, which affect the beam quality especially for high laser powers. To reduce these effects so called variable reflectivtiy mirrors (VRM) have been introduced (1) and investigated especially for solid state lasers (2). So far most investigations have been carried out on unstable VRM-resonators.
Asymmetric, low confinement GaAs/AlGaAs DQW laser diode with optical trap layer for high power operation
Authors: Buda M. , van der Vleuten W. C. , Iordache Gh. , Acket G. A. , van de Roer T. G. , van Es C. M. , van Roy B. H. , Smalbrugge E.
Published: February 2023

This paper reports on low confinement (Γ= 7.5 x 10-3/well), DQW 2 x 8 nm asymmetric laser diode structure designed for high power operation [1]. The low value of Γ is achieved by adding an optical trap layer at one side of the QW’s. A significant part of the optical field is trapped in the n-type Al0.20Ga0.80As optical trap layer with a thickness cf about 0.2 μm, as shown in fig. 1.
Optimisation of flared amplifier heatsinking by finite element analysis
Authors: Jubber M. G. , McIlvaney K. , McLaughlin A. J. , Marsh J. H. , Aitchison J. S. , Troupe C. E. , John P. , Wilson J. I. B.
Published: February 2023

Diamond is an ideal material for use in a diode laser heatsink as it has the highest room temperature thermal conductivity of any material. However, until now it has only been available in a planar, polished format. We describe the fabrication of a diamond heat-spreader with an integral optical fibre alignment V-groove. Firstly a sacrificial silicon substrate was patterned by anisotropic wet etching to produce V-shaped ridges and grooves. The diamond was then deposited by microwave plasma chemical vapour deposition (CVD) [1] over the micromachined silicon features. Figure 1 shows a free standing diamond V-shaped structure after removal of the silicon template. The thickness of the diamond film was conformal over the micromachined silicon ridges and grooves.
Transverse mode selection in external—cavity vertical—cavity surface-emitting lasers: Noise properties and thermal effects
Authors: Valle A. , Dellunde J. , Pesquera L. , Shore K. A.
Published: February 2023

The modification of the transverse mode structure owing to optical feedback (OF) has been studied in a vertical-cavity surface-emitting laser (VCSEL) supporting the two lowest order modes (LP01 and LP11) [1]. Preferential excitation of either mode can be effected by appropriate choice of optical feedback delay, τ [1]. On the other hand, solitary VCSEL supporting those modes has low mode partition noise (MPN) as is seen from its double peak RIN spectrum [2] (see Fig. 1a). In this work we study the RIN spectrum of a multi-mode cylindrical weak index guided VCSEL subject to weak optical feedback. The model incorporates the spatial dependence of carrier and optical field profiles, and Lang-Kobavashi rate equations [1]. We show that the RIN double peak structure and low MPN are maintained in the presence of OF. Variations in τ are shown to alter the RIN spectrum from a twin peak to a single peak structure due to transverse mode selection. It is also shown that multiple reflections in the external cavity can affect the mode selection depending on τ. The impact of thermal effects is also taken into account through the consideration of typical current dependent wavelength shifts. Narrower current ranges in which a particular transverse mode is selected are obtained when ohmic heating is considered. Finally, the effect of ohmic heating on RIN characteristics will be also addresed.
Novel Hot Electron Light Emitter
Authors: Vickers A. J. , Aiyarak P. , Walker A. B. , Watling J. R. , Roberts J. S.
Published: February 2023

One current growth area in the field of optical communications is that of wavelength division multiplexing (WDM). One demand of WDM is a set of devices or a single device capable of emitting a range of wavelengths.
Annealing and degradation effects under intense laser excitation in ZnSe based laser diode structures.
Authors: Jordan C. , Donegan J. F. , McCabe E. M. , Taniguchi S. , Hino T. , Nakano K. , Ishibashi A.
Published: February 2023

Green laser diodes based on II-VI wide band gap semiconductors are subject to degradation under current injection. Considerable progresses have been made in material quality and a 100 h cw operation was reported by Sony in early 1996.
Optical Gain Calculations for Near-Infra-Red Intersubband Semiconductor Lasers
Authors: Cheung C Y L , Rees P. , Shore K A
Published: February 2023

Intersubband semiconductor lasers have attracted considerable attention following the development by Faist, Capasso et al of Mid-Infra-Red (MIR) Quantum Cascade lasers. Quite considerable progress has subsequently been made in improving the performance of those devices and work has been undertaken to assess the operating characteristics and specifically including the direct current modulation capabilities of such lasers [1]. More recently a self-consistent analysis of the laser dynamics was undertaken using calculated carrier lifetimes and optical gain in these devices[2].
Thin-film microstriplines with Bencocyclobutene probed by Electric Field-induced Second-harmonic Generation
Authors: Nagel M. , Heiliger H.-M. , Dekorsy T. , Kurz H. , Hey R. , Ploog K.
Published: February 2023

Polymer materials strongly improved the propagation properties in several types of waveguides.1 Another important advantage of the polymer is, i.e. that the polymer itself can be utilized as a probe for contactless and non-invasive on-chip measurements of high frequency electric fields up to 2 THz via electric field-induced second-harmonic (EFISH) generation.2
Coherent quantum-well absorber mode locking for excitation dependent dephasing
Authors: Kalosha V. P. , Müller M. , Herrmann J.
Published: February 2023

Recently the shortest pulses directly out of a Ti:sapphire laser as short as 6.5fs has been generated by use of single quantum well (SQW) GaAs absorber [1]. Since this laser produces pulses with durations shorter than or comparable to the polarization dephasing time and sufficient power for Rabi flopping of the excited carrier density, the noninstantaneous response of the absorber polarization has to be taken into account. We develope the theory of coherent absorber mode locking taking into account also inhomogeneous broadening of the semiconductor transition by freely movable carriers and Coulomb renormalization of the transition frequency in the scope of semiconductor Bloch equations. Photo-echo measurements in highly excited GaAs yield a decreasing of the effective dephasing with increasing of the laser excited carrier density as T2 ∝ N-1/3. In the SQW absorber the center wavelength of 750nm is well above the bandedge of the GaAs SQW at 870nm and the broad pulse spectrum excites mainly 3D carriers above the confinement depth. We have shown that Rabi-flopping is self-consistently produced due to sub10fs pulse formation at TW/cm2 intensities corresponding to an excited carrier density up to 1020cm-3.
Measurement and calculation of the critical pulsewidth for gain saturation in semiconductor optical amplifiers
Authors: Borri P. , Mørk J. , Hvam J. M. , Mecozzi A.
Published: February 2023

Active semiconductor optical waveguides are essential components in many recently proposed devices for high-speed optical signal processing. It is well known that ultrafast carrier dynamics, like carrier heating and spectral holeburning, lead to gain non-linearities, which restrict the modulation bandwidth of semiconductor lasers. In the case of pulse amplification, these non-linearities lead to a pulsewidth dependence of the gain saturation [1]. A critical pulsewidth can be defined [2], which separates two qualitatively different regimes: a long-pulse regime, where the gain is determined by the pulse energy only, and a short-pulse regime, where the gain also depends on the pulsewidth. Calculated critical pulsewidths are on the order of several picoseconds [1], which is getting in the range of pulses being explored for ultrafast optical signal processing. Experiments that we are aware of. however, do not investigate the detailed dependence of the saturation energy versus pulse duration, and subsequently do not allow extraction of the critical pulsewidth.
Gain at the End Configuration of a diode-pumped, Kerr-lens mode-locked Cr:LiSGaF Laser
Authors: Ruβbüldt P. , Gäbel K. , Du K. , Lebert R. , Loosen P. , Poprawe R. , Valster A.
Published: February 2023

Currently the widespread application of fs-lasers is limited by price and complexity. One approach for user-friendly systems are diode-pumped Kerr-lens mode-locked (KLM) fs-lasers with Cr:LiSGaF or Cr:LiSAF as the gain-medium. However bulky optical systems are necessary, to focus the laser diodes through the folding mirrors of a standard x- or z-fold cavity into the crystal. Efficient KLM and a small lasing threshold requires to focus the resonator mode tightly into the laser crystal. But in this case the poor beam quality of available red single emitter diode lasers prohibits an efficient mode matching.
Influence of higher-order phase dispersion in a femtosecond Kerr-lens mode-locked forsterite laser: dispersive wave and pulse splitting
Authors: Chassagne B. , Jonusauskas G. , Oberlé J. , Rullière C.
Published: February 2023

The effects of higher-order intracavity phase dispersion are studied: third-order dispersion (resp. fourth-order) gives rise to a linear dispersive wave (resp. pulse splitting). Experimental observations fit well with those of theoretical calculations.
Two-Photon Photoconductivity in Semiconductor Waveguide Autocorrelator.
Authors: Skovgaard Peter M. W. , Mullane Rory J. , Nikogosyan David N. , McInerney John G.
Published: February 2023

Recently autocorrelation measurements of short pulses has been accomplished using simple semiconductor devices such as photodiodes, a technique which offers several advantages in cost, simplicity, sensitivity and robustness over conventional autocorrelation technique based on second harmonic generation (SHG) in thin (10 - 100 μm) nonlinear crystals.
Frequency Agile CO2-Tea Laser Based Dial-Lidar System for Range-Resolved Urban Pollution Monitoring
Authors: Gasmi T. , Zeaiter H. , Ropero G. Miñana , Casado A Navas , Ureña A González
Published: February 2023

In this paper, the use of a single and compact pulsed infrared CO2-TEA laser Dial system for range-resolved remote sensing of atmospheric urban pollution is presented. The Use of CO2-TEA lasers in this context requires operation at maximum output energy or peak power throughout a wide spectrum of CO2 transitions in the 9 to 11 μm bands. This lidar system uses a CO2 transversely excited atmospheric (TEA) frequency agile laser that achieves rapid tunability by using a small, flat copper minor mounted on a non-resonant galvanometer. The copper mirror folds the laser mode onto a grating at discrete angles to select each wavelength. The laser is capable of switching reliably between lines at a rate of 200 Hz. The most dominant time constant attributed to CO2-TEA laser pulses whose nitrogen tail can extend for several microseconds, limiting the range resolution of the lidars to some hundreds of meters unless pulse-deconvolution techniques1 are adopted, is circumvented in this work by the use of a plasma shutter. Of course, electro-optic crystals such as CdTe and CdSe could be used between polarisers to achieve the same results. However, the minimum permissible clear aperture due to the large laser beam diameter is approximately 9 to 30 cm2, requiring an excessively large and expensive electro-optic crystal; telescopic reduction of the beam diameter could be performed to reduce the required aperture at the expense of the beam divergence. This sealed plasma-shutter pulse clipper filled with helium to an optimum pressure of 500 mbars is shown in Fig. 1.
TE-CO2 Injection Laser: Status and Perspectives
Authors: Martellucci S. , Richetta M. , Bellecci C. , Gaudio P.
Published: February 2023

Within the framework of our LIDAR activity, devoted to air pollution measurements, we realised the injection of a continuous carbon dioxide laser into a high power TE-CO, laser, to get the possibility of better analyse return signal responses and to realised a Doppler wind velocimeter.
Imaging Bypass System with Correction for Primary Mirror Distortions
Authors: Vasil’ev M.V. , Berenberg V.A. , Leshchev A.A. , Semenov P.M. , Venediktov V. Yu.
Published: February 2023

Dynamic plain (thin) holograms, recorded in the optically addressed liquid crystal spatial light modulators (OA LC SLM) can be successfully used for correction for distortions, imposed by the elements of imaging telescopes1,2. In this case one can realise dynamic correction and real time imaging of various objects, including self-luminous.
Electro-Optic Properties of Poled and Unpoled Copolymers
Authors: Michelotti F. , Taggi V. , Bertolotti M.
Published: February 2023

The knowledge of the nonlinear optical properties of organic polymers has reached a stage of maturity after a couple of decades of intense investigations. In particular the second order nonlinear optical properties of poled polymer films have been widely explored; their application targets in integrated optoelectronics start to be met, opening the way to a whole generation of high frequency electro-optic modulators. However, in order to make these materials really applicable in the manifacturing of long living and reliable devices, a serie of problems still have to be completetely solved. In particular the temporal stability of the orientational distribution of the nonlinear guest chromophores, the chromophores’ chemical stability under intense illumination conditions and the presence of parasitic χ(3) contributions to the second order nonlinear optical response.
Enhanced Second Harmonic Generation in Organic Crystalline Microcavities
Authors: Josse Dominique , Ledoux Isabelle , Gauvin Serge , Zyss Joseph
Published: February 2023

The strong enhancement of optical electromagnetic fields inside microcavities based on laser or nonlinear optical (NLO) materials opens promising perspectives in terms of reduction or even cancellation of laser threshold or demonstration of highly efficient frequency conversion in very thin nonlinear samples. We report here on the elaboration and optical characterization of Fabry-Perot (FP) type microcavities made of 4-Nitrophenyl-L-prolinol (NPP) crystal, and experimentally evidence cavity-enhanced second harmonic generation (SHG) around 1.15 µm. The FP cavity is made of a NPP crystalline layer (thickness 11 µm) sandwiched between two dielectric mirrors (maximal reflectivity R = 95% centered at 1.15 µm). After capillary filling, the polycrystalline sample is placed inside a furnace with a transparent window allowing for microscope observation of the corresponding area, which creates a «cold » zone where recrystallization may be seeded. Large single crystalline domains (5×2mm2) are obtained at the outcome of the cooling process.
Diode-pumped continuous wave laser oscillation of Yb,Ho:YSGG at 1.2µm
Authors: Diening A. , Fomasiero L. , Kueck S. , Huber G.
Published: February 2023

The Yb-Ho system is well known for its multiple possibilities of laser transitions from the visible to the middle infrared spectral region. The ytterbium codoping offers the possibility to use laser diodes at 970 nm as efficient pump sources. The energy is absorbed by Yb3+ and then transfered to the 5I6-level in Ho3+, which is the upper laser level. The bleaching of the 3I8 ground state which is the lower laser level is realized by the following processes: First of all, via the energy transfer from ytterbium. Furthermore, the 5I7-level with its long lifetime of 10 ms is used as a reservoir. From this level efficient upconversion and excited state absorption processes to higher lying levels take place which not only feed population to the upper laser level but moreover prevent Ho3+-ions from relaxing to the ground state (Fig. 1).
Cr4+:forsterite: What is the optimum pump wavelength?
Authors: Kuleshov N.V. , Podlipensky A.V. , Shcherbitsky V.G. , Lagatsky A.A. , Mikhailov V.P.
Published: February 2023

Cr:forsterite is one of the first laser materials from the family of Cr4+-doped crystals. The efficiency of Cr:forsterite lasers does not exceed 37% and is much lower then the quantum defect limited value of 87%[1-3]. Thus, the choice of optimum pump wavelength for Cr:forsterite is still important, especially for diode laser pumping. One of the possible loss mechanisms is excited state absorption at pump wavelength [4].
Direct diode-pumped room-temperature Cr4+:YAG laser
Authors: Sorokina I. , Naumov S. , Sorokin E. , Wintner E. , Shestakov A. V.
Published: February 2023

The Cr4+:YAG laser, first reported in [1], is a unique laser source, tunable over an attractive for many applications wavelength range of 1.34-1.6 µm [2]. The diode-pumping of Cr4+-doped materials, however, remains a challenging task due to difficulties in growing of the crystals with high Cr4+concentration. The recently reported diode-pumped operation of Cr4+:forsterite and Cr4+:Ca2GeO4 required the ideal beam of the MOPA source [3] and no results on direct diode-pumping of any Cr4+-doped material with conventional diode arrays are known to us at the moment.
Polarization threshold switches based on ordered GaInP
Authors: Krauß J. , Kippenberg T. , Kiesel P. , Döhler G.H. , Greger E. , Schweizer H.P. , Moser M.
Published: February 2023

The material system (Al) GaInP is very interesting for opto-electronic devices in the visible spectral range. Under suitable growth conditions (Al)GaInP epitaxial layers show a spontaneous self ordering of the CuPtB-type [1]. For growth in the [100]-direction this ordering results in alternating Ga-rich and In-rich {111}B planes. The mono-atomic superlattice causes significant changes of the electronic structure compared to the normal disordered alloy. In particular, ordered crystals exhibit a band gap reduction and a valence band splitting at the T-point. As a consequence of dipole selection rules, transitions between the highest valence band and the conduction band are forbidden for light polarized parallel to the ordering direction. This leads to a strong polarization anisotropy even for light propagating normal to the {100} crystal surface.
Theoretical and Experimental Studies of Back-Gated Metal-Semiconductor-Metal Photodetectors
Authors: Vickers Anthony J. , Mashayekhi Hamid R.
Published: February 2023

The back-gated metal-semiconductor-metal photodetector is a hybridisation of a metal-Semiconductor-metal Photodetector and a pin photodiode. Top contacts are made to two n-regions which are isolated by etching down to the intrinsic region. A third contact is made to the bottom p-region(see figure 1).
Metal-Semiconductor-Metal Near Infrared Light Detector Based on Epitaxial Ge on Si
Authors: Colace L. , Masini G. , Galluzzi F. , Assanto G. , Capellini G. , Di Gaspare L. , Palange E. , Evangelisti F.
Published: February 2023

Due to the ever growing use of optical fibers in communications, for both long distances and local area networks, there is an increasing effort toward the realization of high speed and high efficiency optical detectors, operating in the low-absorption regions (1.3-1.55µm) of silica fibers. Although III-V semiconductors provide high detection efficiency in the range of interest, incorporating them in the well-established Si-based very large scale integration technology is difficult and expensive[1]. Ge-on-Si structures represents a viable alternative solution for near infrared photodetection, owing to their narrow band gap and full compatibility with silicon technologies. Pure germanium, indeed, represents the best candidate for absorbing in 1.3-1.55 µm photodetectors, due to its direct bandgap of 0.85eV. However, owing to the high lattice mismatch with Si, it is not easy to obtain Ge films with characteristics suitable for integrated electronics: thickness (efficiency of the device), flatness (realization of submicron lithography), defect-free structure (high-speed).
Room temperature CW operation of InGaAsP/InP microdisk lasers
Authors: Courtney D , O’Brien P , McInerney J G , Corbett B
Published: February 2023

Microcavity lasers (and the closely related photonic bandgap materials) use wavelength scale dimensions to filter and select photon modes. They have enormous potential both for fundamental research and development of new optoelectronic devices and systems [1]. Although one-dimensional microcavities (such as most VCSELs) are relatively straightforward to fabricate, they do not produce strong mode quantization effects: the standard semi-classical theory predicts that a 1-d microcavity will modify the radiative transition by at most a factor of three 3, and observed enhancements have been considerably less due to nonideal effects.
Crosstalk due to Longitudinal Spatial Hole Burning in Gain-Clamped Semiconductor Optical Amplifiers
Authors: Pleumeekers J.L. , Dupertuis M.-A. , Hessler T. , Selbmann P.E. , Deveaud B.
Published: February 2023

Gain-clamped semiconductor optical amplifiers (GCSOA’s) are promising candidates for wavelength division multiplexing (WDM) applications due to their low inter-channel crosstalk and high saturation output power, obtained by the gain-clamping [1]. However, in this presentation we will show that, although the gain is clamped, some inter-channel crosstalk still occurs due to longitudinal spatial hole burning.
Reduced Wavelength-Count Vector-Addressed Multi-Stage Access Network Based on Phased-Array Optical Routers
Authors: Parker M.C. , Farjady F. , Walker S.D.
Published: February 2023

Wavelength-routing [1] in the access network offers the prospect of high security and Gbit/s capacity to the end user. However, for large numbers of wavelengths (e.g. >32) issues of stability and precision become important. In this paper, we present a novel 3-stage switched ATM access architecture, shown in fig. 1, which (while maintaining the above benefits) can route to large numbers of customers using a minimal set of wavelengths, and also allows an evolutionary path from current passive optical networks (PONs). We exploit the functionality of cascaded programmable and passive arrayed-waveguide gratings (AWGs) [2], to provide a multi-dimensional bi-directional addressing strategy, based on spatial, wavelength and temporal multiplexing. The same network can be used for independent upstream routing by utilising the reciprocal input and output AWG ports, and taking advantage of their cyclic-shifting properties to avoid potential collisions. Stage 1 in the proposed architecture is a P-way splitter with semiconductor optical amplifiers (SOAs), stage 2 is an active coarse AWG with Q output ports, and stage 3, located at the distribution point (DP) near the end users, is a passive coarse AWG with R output ports. To upgrade from existing PONs, the 3rd stage can also equally consist of an R-way optical splitter, with coarse wavelength-filters at the customer end. At the DP, the coarse AWGs (insensitive to temperature changes > 70°C) each have R=24 output ports, which allows the architecture to map onto 99% of the current UK network topology. The parameter R also defines the number of wavelengths to be 24. The total number of customers served is the product PQR=6912, where P=12, Q=R=24. Since only coarse demultiplexing is performed, the need for stable and accurately defined wavelength sources at the exchange and end user is obviated.
Detection of HCl at the ppb level with a DFB laser based spectrometer
Authors: D'Amato F. , De Rosa M. , Corsi C. , Modugno G. , Inguscio M.
Published: February 2023

In several industrial processes there is a growing demand for a fast and sensitive detection of HCl, in order to reduce the pollution due to that molecule. We realized a compact spectrometer based on distributed feed-back (DFB) diode laser, which adopts a two-tone frequency modulation technique, for reaching a detection limit of few ppb. This technique moves the demodulation frequency in a region where the laser excess noise can be reduced to a lower level (10 MHz - 1 GHz).
Diagnostics of Surface and Bulk Structural Phase Transitions in SrTiO3 Single Crystal by Second Harmonic Generation
Authors: Sherstyuk N.E. , Sigov A.S. , Mishina E.D. , Rasing Th. , Misuryaev T.V. , Aktsipetrov O.A.
Published: February 2023

Second harmonic generation (SHG), has often been used to study structural phase transitions in solids, in particular the phase transitions from a non-centrosymmetric to a centrosymmetric phase, as it is extremely sensitive to this. We show here that the sensitivity of SHG to the spatial fluctuations of the order parameter allows one to study the details of a phase transition from a centrosymmetric to another centrosymmetric phase and to distinguish the contributions to the SHG intensity from the bulk and from subsurface layers of a crystal.
Simple method for compensation of thermally-induced birefringence in high-power solid-state lasers
Authors: Clarkson W. A. , Felgate N. S. , Hanna D. C.
Published: February 2023

Progress in power-scaling diode-pumped lasers has been hindered by thermal effects; notably thermal lensing and stress-birefringence. For applications requiring a linearly polarised output (e.g. nonlinear frequency conversion and Q-switching), the most serious problem is the depolarisation loss resulting from stress-induced birefringence which dramatically reduces the efficiency of low gain lasers at high pump powers. Various techniques for compensating stress-induced birefringence have been described (e.g. [1],[2]), but which are not well-suited for low gain end-pumped lasers employing a single laser rod.
A High Repetition Rate Electro-Optically Q-switched Diode Pumped Nd:YVO4 Laser
Authors: Bente E. , Robertson G. , Ferguson A. I. , Barr J.
Published: February 2023

Several laser applications require visible or near ultraviolet light, sometimes tuned, at average powers of the order of Watts or higher and in a high quality beam. Also repetition rates of tens of kHz are often a necessity for reasons of productivity. The required wavelengths can be generated using non-linear optical techniques such as OPO’s pumped by a Q-switched diode pumped solid state laser operating around 1 micron. Acousto-optically Q-switched lasers have high repetition rates and can have high average powers, but produce relatively long pulses (typically over 100 ns) [1]. The efficiency of the non-linear conversions will increase when the pulse length can be reduced to the order of tens of ns. This argument led us to the development of a diode pumped electro-optically Q-switched Nd:YVO4 laser, operating at 1064 nm, with a pulse length between 10 and 20 ns at repetition rates up to 20 kHz, output powers of over 10 Watt in a high quality, polarised output beam. The challenge in this development is the combination of these requirements in one device.
High average power diode end-pumped passively Q-Switched solid state laser
Authors: Wu N. , Du K.-M. , Falter S. , Loosen P. , Poprawe R.
Published: February 2023

Passively Q-Switched solid state lasers are of high interest for many applications like marking that do not require accurate repetition rates. With Cr4+ doped YAG as a saturable absorber it is possible to design cost effective passively Q-Switched solid state lasers operating highly efficient. Up to now powers higher than 180W have been reported in lamp pumped NdYAG lasers [1] at more than 70% efficiency. However the highest reported power for diode-laser end-pumped Systems to our knowledge is about 1.5W [2]. We investigated a NdYAG laser end pumped by fibre coupled diode bars at pumping wavelength. With the Cr4+ crystal in the cavity passive Q-switching could be obtained. Different crystals with varying small signal transmission have been tested as well as different resonator designs and output copuling rates. Our highest yet achieved value is 5.6 W averge power at 1064nm at 22.7 W input power a saturable absorber, whose small signal transmission was 89% . The average repetition rate at this value is 11.5 kHz and the pulsewidth 32ns. The cw-output without the saturable absorber at this value is 9.2 Watts. A plane/plane cavity with a length of 116 mm was employed. Further optimisation should lead to an increase of either the Q-Switch effiency and the overall efficiency. The application of different laser crystals like Nd:YVO4 promises even higher repetition rates and average powers at comparable pulselengths. Experiments on the verification and optimisation as well investigations on the pulselength are in progress and will be reported. Furthermore, frequency doubling of the laser output power is targeted and the results will also be reported.
Semiconductor Ring Laser Gyroscopes
Authors: Ikeda Masahiro , Taguchi Kozo , Fukushima Kaname , Ishitani Atsuyuki
Published: February 2023

Semiconductor ring lasers have many capabilities of realizing new functional devices. One interesting application of a semiconductor ring laser is a semiconductor ring laser gyroscope, hereafter called a S-RLG. S. Oku et al. demonstrated the low threshold current cw operation of 50 μm square-shaped ring-resonator-type semiconductor laser[1] which consisted of straight wave guides and four total reflection minors. M. Ikeda et al. proposed self-detection method of lasing characteristics for semiconductor ring lasers without branching optical lasing power[2]. The lasing power and the line width as a function of the injection current have been measured with detecting the RF power by the terminal voltage change of a ring LD. If a semiconductor ring laser operates as an optical inertial rotation sensor, a very small and simple optical gyroscope can be realized. To our knowledge this is the first demonstration of a S-RLG.
Room-Temperature Laser Pumped 2-μm Holmium Lasers.
Authors: Sandulenko A.V. , Sandulenko V.A. , Tkachuk A.M. , Titov A.N. , Reiterov V.M. , Ivanov V.N.
Published: February 2023

This work aimed at studying the laser action in YbLiF4:Ho, YbLiF4: Ho,Tm and KYb(WO4)2:Tm,Ho crystals under selective pumping with the 1.047 μm Nd:YLF laser. Also we considered the inverse population formation of working levels of the 2-μm transition in holmium ions.
A synthetic model for the Nd-doped fiber laser
Authors: Chartier T. , Sanchez F. , Stéphan G.
Published: February 2023

The Nd-doped fiber laser operating at 1.08 μm has remained an excellent candidate for the study of dynamics in fiber lasers. Dynamical polarization properties of Nd-doped fiber lasers have first been reported in [1]. From the experimental point of view, the Nd-doped fiber laser behaves as a two-mode system where the modes correspond to the intensities of the fields polarized along the eigenaxes of the fiber. This fact led to a theoretical modeling of the experimental results in terms of standard two-mode laser equations where phenomenological population inversions and pumping parameters were introduced.
Ultrastable solid state lasers for space science missions
Authors: Peterseim M. , Brozek O.S. , Freitag I. , Tünnermann A. , Danzmann K. , Welling H.
Published: February 2023

Laser metrology has been identified as a key technology of many 21st century space science missions. In particular, this applies to the space-borne gravitational wave detector LISA and the large baseline stellar interferometers. Common features of these interferometers are that under current design they consist of multiple individual spacecraft, formation flying at large separations, and that the relative optical pathlengths over these distances need to be known or even controlled to the nanometer level. Therefore a stabilised laser system and a metrology gauge are required to monitor the optical pathlengths.
Efficiency of Yb-TR3+ Energy Transfer in Up-conversion Pumped Double Fluoride Laser Crystals
Authors: Tkachuk A.M.
Published: February 2023

The double fluoride crystals doped with rare-earth ions are well known as active laser media for laser operation in a wide spectral range from 0.325 to 7.2 μm under laser diode pumping including also the cases of resonant up-conversion pumping and non-resonant avalanche pumping.
Upconversion in Tm:LaF3 under pulsed excitation
Authors: Lim Ki-Soo , Oh Yoo-Mi , Lee Soo-Cheon , Nakamura Arao
Published: February 2023

Upconversion emission at 480 nm in Tm:LaF3 crystals was reported with continuous excitation in the red[l] and the excitation at 635.2 nm produced photon avalanche upconversion emission. However, the upconversion emission has not been investigated in this crystal for pulse laser excitation. In this paper, we report the separation of two kinds of two-step upconversion processes for the blue upconversion emission in the crystal. One process is a single pulse sequential two-step absorption process of the 3H6 → 3F2 and 3H4 → 1D2 transitions and the other two-step absorption process is produced by the successive pulse excitations from 3H6 to 3F2 and from 3F4 to 1G4. Pulse repetition rate dependence of the emission at 480 nm with an excimer-laser pumped dye laser excitation in Fig.1 shows the separation of two upconversion processes. The emission at 656 nm excitation even with 1 Hz indicates the single pulse two-step upconversion, although it increases due to the accumulation of the population in the 3H4 level when the repetition rate does.