bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface-enhanced second-harmonic generation using gratings: phase-matching conditions
Authors: Neviere M. , Popov E.
Published: February 2023

There is a general belief that phasematching between resonances at pump and signal frequency can significantly enhance the performance of nonlinear corrugated systems. These resonances can be plasmon-polariton surface waves in case of metallic substrates and/or waveguide modes inside the nonlinear dielectrics. This belief in the phase-matching comes from general physical arguments—guided wave excitation leads to field enhancement at the pump frequency that can be properly coupled to a mode at the second harmonic frequency. However, only recently with the development of rigorous methods for studying the nonlinear effects, it becomes possible to check the role of the phase-matching.
Prospects of nuclear-pumped lasers
Authors: Dyachenko P. P.
Published: February 2023

The physical basis of a nuclear-pumped laser (NPL) operation is a fundamental phenomenon—the excitation and relaxation of nuclear-induced plasmas. Nuclear-induced plasmas is the state of matter that arises when charged products of nuclear reactions are stopped in matter and simulate the ionization and excitation of its atoms. The most important feature of such plasmas is its recombination nonequilibrium which virtually means that stopping of nuclear reaction products forms practically “ready" laser active medium in a matter. Thus it is possible to say that NPL is a device that produces a direct conversion of nuclear energy into energy of laser radiation.
Ablation of tissue by 308-nm excimer laser pulses is accompanied by explosive water bubble formation
Authors: van Leeuwen Ton G. , Jansen E. Duco , Motamedi Massoud , Welch A. J. , Borst Cornelius
Published: February 2023

Currently, various types of pulsed lasers are used for ablation of tissue. Owing to their small penetration depth, mid-infrared and ultraviolet lasers are attractive candidates for precise tissue cutting. Furthermore, both the mid-infrared and ultraviolet laser pulses can be delivered via flexible fibers, which allows ablation of tissue in a water environment and in the human body. The mid-infrared holmium (wavelength λ = 2.09 μm) and thulium (λ = 2.01 μm) laser ablation is based on the absorption and subsequent vaporization of tissue water. As a result, with each laser pulse, a rapidly expanding and imploding vapor bubble (lifetime τ ≈ 500 μs, diameter ∅ up to 3 mm) is formed.1
Safety device for fiber-optic delivery systems
Authors: Schena A. , Falciai R.
Published: February 2023

Fiber-optic delivery systems for laser sources are now widely used in the biomedical field. In this work a control device that improves the safety of the system is described. The proposed device has been designed and realized in order to interrupt the laser emission in case of fiber damage, in any point of the fiber, and in presence of misalignments between input optic and fiber, source anomalous behavior, or input optic damage.
A low drive voltage LiNbO3 electro-optic modulator for 2.5 Gbit/s and beyond B-ISDN application
Authors: Pan J. J. , Su W. H. , Xu J. Y. , Cao S. , Shih M.
Published: February 2023

Broadband SONET (Synchronous Optical Network), SDH (Synchronous Digital Hierarchy), and ATM (Asynchronous Transfer Mode) are widely deployed in public and private networks. OC-48/SDH-16 equipment of 2.5 Gbit/s and high speed network components beyond 2.5 Gbit/s are gaining popularity in various B-ISDN systems. Wavelength chirping of laser diode (LD) creates a hurdle in Gbit/s directly modulated optical transmitter design. Practically, transmitter consisting of a narrow linewidth LD source and an external electro-optic modulator (EOM) can provide a minimum chirping effect and is suitable for multigigabit transmission.1,2 Currently, the typical drive voltage of 3 GHz LiNbO3 EOM is about 3~4 V at 1310 nm. Therefore, the required high speed electronic drive circuits are costly and thus limits the mass deployment of the external modulated transmitter modules. In this paper, we report the demonstration of a low drive voltage (Vx = 1.7 V) EOM with optical modulation bandwidth of 5 GHz.
High harmonic generation
Authors: Burnett Keith
Published: February 2023

It is now possible to describe the response of single electron systems to laser fields around one atomic unit. In such intense fields an atom or ion may generate a comb of harmonics that extends far into the XUV. Many experimental and theoretical groups are now studying this process and assessing the relative merits of different species and laser wavelengths for the efficient production of harmonics. This is a very complex matter indeed involving microscopic—single electron multiphoton response as well as macroscopic propagation of intense light in an ionising medium—issues.
Cavity QED in multiple quantum wells
Authors: Weisbuch C.
Published: February 2023

Summary not available.
High average power, diode-pumped solid-state lasers
Authors: Krupke William F.
Published: February 2023

The recent development of semiconductor laser diode arrays producing high average power (CW or near unity pulsed duty factors) at high efficiency is enabling the design, development, and commercialization of high average power-diode-pumped solid-state lasers (DPSSLs) with excellent output beam quality. The high compactness, high reliability, and radiation-delivery-by-fiber achievable with all solid-state lasers with high output beam brightness has prompted interest by a wide variety of applications users. Although near resonant pumping with narrowband diode-pump arrays reduces specific thermal loadings of typical laser gain media by factors of several-fold compared to flashlamp pumping, the realization of high average power DPSSLs (tens of watts to kilowatts) requires the development and/or implementation of novel laser architectures, laser cavity resonators, laser medium geometries, and pump array coupling optics.
Detection of amplitude-and-phase structure of ultrashort pulses by the method of spectral nonlinear optics
Authors: Mazurenko Yu.T. , Putilin S.E. , Spiro A.G. , Beliaev A.G. , Yashin V.E. , Chizhov S.A. , Vavilov S.I.
Published: February 2023

Spectral nonlinear optics uses nonlinear interaction of spatially decomposed ultrashort pulses [1,2]. In the present work we show the possibility of the amplitude-and-phase imaging of ultrashort pulses based on three-wave spectral nonlinear optics.
Wavelength Conversion of Sub-Picosecond Optical Pulses by Four-Wave Mixing in a Semiconductor Optical Amplifier
Authors: Kawaguchi Hitoshi , Inoue Jun
Published: February 2023

Nondegenerate four-wave mixing (NDFWM) in semiconductor optical amplifiers (SOA's) was studied both as a spectroscopic tool and as a wavelength conversion technique. The pump-probe detuning has been extended up to 4.3 THz based on ultrafast nonlinear gain dynamics including carrier heating and spectral-hole burning [1]. Unlike wave mixing in passive nonlinear media, the NDFWM efficiency in SOA's is limited by the gain saturation [2]. This limit can be overcome by mixing short optical pulses.
Two-micron CW laser operation and spectroscopic investigation of Tm3+ doped CaYAlO4 single crystals
Authors: Moncorge R. , Kerbrat Ph. , Borel C. , Wyon Ch.
Published: February 2023

As reported recently [1], some of the infrared spectroscopic properties of Tm doped CaYAlO4 such as a large and broad 3H6 → 3H4 absorption cross section (~ 1.5 × 10-20 cm2) near 800 nm and a large and broad 3F4 → 3H6 stimulated emission cross section (~10-20 cm2) near 1900 nm, are very attractive for tunable two-micron laser operation using diode pumping with relaxed diode wavelength control.
Neodymium-doped gallium lanthanum sulphide glass laser
Authors: Schweizer T. , Hewak D.W. , Payne D.N. , Jensen T. , Huber G.
Published: February 2023

Chalcogenide glasses are compound glasses containing one or more of the chalcogen elements S, Se, and Te and metals such as Ga, As, and Ge1. The main applications of these glasses are their use as infrared transmitting windows and as "light pipes” for infrared radiation when pulled into fibre form. The infrared transparency is caused by the low phonon energies of the glass structure. The low phonon energies also reduce the non-radiative decay rates in rare-earth doped chalcogenide glasses making them interesting for applications such as lasers and fibre amplifiers2,3,4.
Integrated Grazing Incidence Cavity for Single Mode Pulsed Lasers
Authors: Gloster L. A. W. , Binks D. J. , King T. A. , McKinnie I. T.
Published: February 2023

Tunable single longitudinal mode (SLM) operation is essential for many spectroscopic applications. Often, however, reaching the required spectral purity in dispersive cavity geometries can compromise the output power of the laser and cause high oscillation thresholds. We report on a grazing incidence cavity which has been integrated with a linear cavity to form a Michelson interferometer with the inclusion of an inexpensive optic. Dramatic improvements in output efficiency and threshold are observed in this cavity over the conventional grazing incidence design1,2. The additional optic, in this case, is a glass slide known as the zero-order mirror (figure 1). The interferometric nature of the cavity places an additional constraint on the allowed resonant modes, since each cavity must be simultaneously satisfied, resulting in an increase in the cavity mode spacing. This allows a single mode to be readily isolated. By modelling the cavity geometry, we can predict the mode behaviour accurately and position the optical components to maximise the mode spacing. In order to demonstrate this, we have designed a pulsed Ti:sapphire laser pumped at 532 nm, although in practise other gain media could be used. Using our software-driven piezoelectric transducer (PZT) on the zero-order mirror, we are able to lock the cavity to a single mode with a bandwidth of 200 MHz, limited by the resolution of the 10 GHz etalon used, whilst maintaining a tuning range of > 100 nm.
Excimer Laser Crystallisation and Processing of Polysilicon Thin Film Transistors
Authors: Pribat D.
Published: February 2023

Although some polysilicon-based products, such as liquid crystal light valves, are already on the market, it is generally agreed that they are too costly for consumer applications, because they need to be fabricated al high temperature, on quartz substrates, An order to extend the application of polysilicon, low temperature, glass compatible processes have been actively studied over the past few years and pulsed excimer laser processing is new emerging.
Parametric Study of C-N Film Deposition By Reactive Laser Ablation
Authors: Luches A. , Martino M. , Perrone A. , Alexandrescu R. , Mihailescu I.N. , Mengucci P.
Published: February 2023

The interest about carbon films has recently increased because of the deposition of diamond films and the prediction of the existence of a covalently bound C-N solid with characteristics comparable or better than those of diamond [1]. Reactive laser ablation could represent the simplest technique for carbon nitride synthesis and deposition.
Laser plasma diagnostics by Time of Flight Mass Spectrometry in Laser Ablation of Aluminium Target
Authors: Berardi V. , Amoruso S. , Bruzzese R.
Published: February 2023

Laser ablation by nanosecond high power laser pulses is a topic of increasing interest in plasma physics and material processing technologies. It is applied as thin films deposition technique to a wide range of materials (e g. metals, semiconductors and superconductors). In particular, for metals the value of laser fluence required for significant vaporisation is nearly the same as the threshold value for plasma formation Thus in laser ablation of metals the plume results significantly ionised, and one of the characteristic features resides in the presence of ions with high kinetic energy in the flux of ablated particles. Moreover, the evaporation process is dependent on laser wavelength. Target irradiation by long wavelength (1-10 μm) causes a "thermal evaporation" process, whereas irradiation by short wavelength (e g. 193, 266, or 248 nm) often results in "non-thermal evaporation" processes. On the other hand, operating at intermediate wavelength region (e.g. 532, 355 or 351 nm) usually produces evaporation neither thermal nor photo-physical in nature.
Research on the Ablation Characteristics and Increasement of Electrical Conductivity of C60 Film by 308nm Excimer Laser
Authors: Lou Q. , Ning D. , Dong J. , Wei Y.
Published: February 2023

Direct photoetching or ablation of some materials by pulsed ultraviolet excimer laser and the feasibility of using this for "dry" lithography in microelectronics now promotes wide research interesting. To date, most studies in this field focus on organic polymer. As a direct gap semiconductor, because of some unusual properties derived from its unique football- like molecular structure, C60 material may cause a great influence on the development of semiconductor industry. In this paper, we studied the ablation characteristics of C60 film irradiated by XeCl excimer laser in air and low vacuum. The ablation rate curve and ablation threshold in air were calculated. The physics in ultraviolet photoablation of C60film and the effect of O2 gas was analyzed through comparing the result in air low vacuum. The results of experiment are shown in Fig 1.
Ultrabroad-band sub-10fs Ti:sapphire ring oscillator
Authors: Xu Lin , Spielmann Christian , Krausz Ferenc , Szipöcs Robert
Published: February 2023

Approaching the gain-bandwidth-limit in Kerr-lens-mode-locked (KLM) lasers has been primarily limited by the finite high-reflectivity bandwidth of quarterwave multilayer dielectric mirrors and the finite constant-group-delay-dispersion bandwidth of prism pairs. Although the discovery of chirped multilayer dielectric mirrors and their subsequent use in KLM Ti:S lasers improved the situation,1 several problems have remained to be solved: i) a quarterwave dichroic mirror used for pump beam coupling and a quarterwave output coupler were employed and hence limited the bandwidth also in mirror-dispersion-controlled systems,1 ii) initiating mode locking becomes more and more difficult for shorter pulse durations. This latter problem relates on the one hand to the low negative GDD required for sub-10fs pulses. On the other hand, self amplitude modulation can not be maximized as suggested before2 due to saturation problems at very short steady-state pulse durations.
Synchronization of Solitary Femtosecond Pulses in a Widely Tunable Two-color Ti:Sapphire Laser
Authors: Fürst C. , Leitenstorfer A. , Laubereau A.
Published: February 2023

Synchronized femtosecond pulses of different wavelengths are desirable for many applications in ultrafast spectroscopy of semiconductors and molecules. Generation of synchronized pulse trains at high repetition rates (~ 80 MHz) was demonstrated in two-color Ti:sapphire lasers [1-3]. Unfortunatly, the tunability of these previously reported systems was strongly restricted, while the pulse durations were limited to above 50 fs. These limitations turned out to be a serious hindrance for widespread applications in experiment.
Oxidation of InAlAs for Long Wavelength Vertical-Cavity Laser Diodes
Authors: Sowada D. , Chung H.Y.A , Stareev G. , Grabherr M. , Weigl B. , Wipiejewski T. , Ebeling K.J.
Published: February 2023

The excellent performance of vertical-cavity surface-emitting lasers (VCSELs) in the wavelength range below 1mm is largely due to the superior properties of the epitaxially grown AlAs-GaAs distributed Bragg reflectors (DBRs). For long wavelength VCSELs there is no material combination for Bragg reflectors with properties as good as AlAs-GaAs. Therefore we decided to explore the possibility of employing InP and oxidized InAlAs as high and low index material in highly reflecting Bragg mirrors at a wavelength of 1 55mm. Here we describe initial results on the oxidation of InAlAs layers.
Titanium Diffused Waveguides in Sapphire
Authors: Hickey I. M B , Anderson A A , Wilkinson J S
Published: February 2023

The development of a broadly tunable waveguide laser offers important advantages in the application of integrated optics to fields such as sensing and spectroscopy. A waveguide laser based on the well known Ti:sapphire laser system, where the gain bandwidth extends over 400nm in the near infra-red, presents an attractive candidate. The realisation of such a device in low cost, high quality sapphire substrates, requires the development of both optical waveguides and the introduction of the active ion. In this paper we report the demonstration of optical waveguides in sapphire, fabricated by the thermal diffusion of titanium, and identify conditions appropriate for the development of a Ti:sapphire waveguide laser.
Relative Intensity Noise of Ti:Er:LiNbO3 Waveguide Lasers
Authors: Sciancalepore D. , Scarano D. , Montrosset I. , Brinkmann R. , Sohler W.
Published: February 2023

The Relative Intensity Noise (RIN) of the Ti:Er:LiNbO3 waveguide lasers [1] has been theoretically analyzed for the first time and compared with experimental data.
Intracavity sum frequency mixing in a Nd:YVO4 miniature laser
Authors: Olson M , Karlsson H , Laurell E
Published: February 2023

Compact blue-green light sources are attractive for many applications. There are several examples of intracavity frequency doubled sources in the blue wavelength region. However, these sources do not prospect well for high-frequency modulation applications, due to the long lifetime of the meta-stable state in the laser host. Risk et al have demonstrated a scheme to circumvent this [1]. J. They utilized intracavity frequency mixing in KTiOPO4 (KTP) of pump at 809 nm and the laser wavelength 1064 nm in a Nd:YAG miniature laser. This non-linear process is non-critically phasematched at room temperature with exceptionally broad temperature and angular tolerances. Nd: YAG, however, has the disadvantage of emitting unpolarized light, thereby prohibiting an efficient energy conversion of the 1064 nm radiation.
Dark Build-up of Photorefractive Gratings After Nanosecond Pulse Recording in BaTiO3 with Two Secondary Trapping Centres
Authors: Ramos-Garcia R. , Damzen M.J.
Published: February 2023

We report on the detailed observation of dark evolution of photorefractive gratings and induced absorption in BaTiO3 after illumination with a single 15 ns pulse from time scales of 500 μs to 50 s. The initial photorefractive grating written by the short pulse evolves into three distinct phases: (1) a fast growth component ~50 ms, (2) slow growth component ~2-3 sec, and finally, (3) a ultralong decay ~30 min. Fig. 1 shows a typical dark evolution of the diffracted signal after single pulse writing. The diffracted signal is observed to increase by an order of magnitude in a few seconds.
Observation of Reflection-grating Photorefractive Double Phase Conjugation
Authors: Roh Won B. , Hengst Gordon T.
Published: February 2023

Photorefractive phase conjugation is one of the most novel nonlinear optical techniques with applications in such areas as image processing, adaptive optics, laser coupling, and pointing and tracking, to name just a few.1 Although almost all of the devices demonstrated thus far have exploited a transmission grating written in a photorefractive crystal because of the lower threshold gain required, devices based on a reflection-grating geometry have the potential for a higher gain and faster speed.. In view of the fact that slow speed has been one of the most serious shortcomings of photorefractive devices in many practical applications, it is evident that a configuration that gives a faster response would be highly desirable. For this reason there has been an increased amount of research activity to develop reflection-grating phase conjugation devices in recent years. Indeed, besides the theoretical analysis by Zozulya, et. al. and Stemklar,3 D’yakov et.al.4 and Honda, et. al5. demonstrated a reflection-grating self-pumped photorefractive ring mirror.
Polarization Characteristics of InGaAs/GaAs Vertical Cavity Surface Emitting Lasers Grown on GaAs(311)A-Oriented Substrates
Authors: Takahashi M. , Vaccaro P. , Fujita K. , Watanabe T. , Mukaihara T. , Koyama F. , Iga K.
Published: February 2023

The vertical cavity surface emitting laser (VCSEL) is recognized as one important device in applications such as optical interconnects, optical communications and so on. Most of VCSELs have been fabricated on (100)-oriented substrates, and exhibit linear polarization. But usually it is unstable due to the small polarization selectivity [1]. The polarization control is, therefore, an important subject for polarization-sensitive applications. One of the control methods is to use the effect of optical anisotropy of strained quantum wells (QWs) grown on (n11)-oriented substrates [2]. We present here the first result on the stable polarization characteristics of a (311)A-oriented InGaAs/GaAs VCSEL operated at room temperature
Noise Behavior of Sub mA Threshold Single-Mode Oxidized VCSELs
Authors: Fiedler U. , Weigl B. , Reiner G. , Ebeling K.J.
Published: February 2023

Oxidized VCSELs show improved performance with respect to optical output power and wall-plug efficiency compared to their proton implanted counterparts [1]. For broadband digital transmission lasers with low intensity noise are required to avoid noise floors [2]. In this paper we study the noise properties of single-mode oxidized VCSELs.
Temporal Pulse Shape of Quantum-Well Vertical Cavity Surface Emitting Lasers
Authors: Schneider H.C. , Jahnke F. , Koch S.W.
Published: February 2023

We analyze the dynamic response of a quantum-well Vertical Cavity Surface Emitting Laser (VCSEL) after optical excitation by femtosecond pulses. For this purpose, a self-consistent treatment of medium and light properties in the VCSEL is necessary since the carriers, which are generated in the active medium of a VCSEL, do not only interact with themselves and the lattice but also with the electromagnetic field in the microcavity. This carrier-photon interaction is of the same order of magnitude as the carrier-carrier and carrier-phonon interaction. Furthermore, the photon density of states is altered appreciably in the high-Q resonator. In our approach all these effects are treated consistently by a quantum mechanical non-equilibrium theory [1].
Monolithically Integrated Semiconductor Optical Sensors
Authors: Zappe Hans P.
Published: February 2023

The use of photonic integrated circuits (PICs) for sensor applications is lucrative due to the ruggedness, compact size, volume manufacturability and high functionality of a monolithic sensor chip. Monolithically integrated optical sensors, being small and with reduced critical physical alignment requirements, may be employed in high-performance optical microsystems, compact multi-sensor arrays or micro-electromechanical systems (MEMS). In the following, we discuss two prototype monolithic sensor devices.
Integrated Optical High-Voltage Sensor Based On a Polymeric Digital Optical Switch
Authors: Lee Sang-Shin , Shin Sang-Yung
Published: February 2023

The integrated optical high-voltage sensors are useful for remote fiber-optic monitoring of high voltages under the dangerous high-voltage environments including poner distribution systems, without electromagnetic interference. They have been mainly implemented utilizing lithium niobate guided-wave diveces such as Mach-Zehnder interferometric modulators, cutoff modulators [1]. However, the modulator type voltage sensors with a single output port are inevitably affected by the changes in the light source power. In this paper, we report a high-voltage sensor utixzing a polymeric Y-branch digital optical switch [2] in an electro-optic polymer. The measurement of ac high voltages is accomplished by using the linear transfer characteristics of the digital optical switch. The logarithmic ratio of optical powers of two output ports may be also used to remove the noise caused by the power fluctuations of a light source, since the logarithmic ratio is independent of the light source power and linearly proportional to applied voltages around the operating bias point. The passive polymeric high-voltage sensor requires no electrical dc biases and no voltage dividers. It is also wavelength insensitive and fabrication-tolerant since it uses the mode evolution effect instead of interference Moreover, the sensing voltage range can be easily extended by controlling the process parameters of polymeric waveguides such as poling voltage, photobleaching time, and polymer layers thickness.
Spatial Mode Analysis of Electromagnetic Fields
Authors: Jenkins R M , Devereux R W J , Blockley A F
Published: February 2023

A novel form of electromagnetic field analyser is proposed and demonstrated. The analyser is based on the use of a coherent local oscillator which is tuneable, in an orthogonal spatial mode sense. The propagation of a complex transverse electromagnetic field F(x,y) can be described in terms of a set of orthogonal spatial modes: Here, E
p
(x,y) is the p
th
mode of the set; A
p
is its modulus and ϕ
p
its phase. Figure 1, illustrates the situation where this field is coherently mixed with the mode E
q
(x.y) from a mode tuneable local oscillator.
Ultrafast All-Optical Switching with Low-Temperature-Grown Semiconductor Materials
Authors: Smith Peter W. E.
Published: February 2023

We will review recent work on the development of low-temperature-grown semiconductor materials that has demonstrated the potential of these materials for ultrafast all-optical device applications. This work has led to an understanding of the dynamics of optically-induced absorption and refractive index changes, and the way m which the optical properties can be tailored by adjusting material growth and annealing conditions. We will then discuss some ultrafast switching and signal-processing devices based on these materials.
Passive fiber ring flip-flop memory based on polarization dynamics
Authors: García-Mateos Jorge , Canal Fernando , Haelterman Marc
Published: February 2023

Optical storage devices are essential elements of future ultra-high bit-rate fiber communications systems in which they will find applications to various vital functions. Pulse pattern storage has been demonstrated in various fiber loop devices [1] that involve pulse control techniques in order to provide timing stability of the bit patterns. Most of these stabilization techniques are based on electrooptic modulation which limits the bit rates to a tenth of Gb/s. Moreover, erasing the data in these storage fiber loops requires switching off the system elect rooptically. Individual bit addressing is therefore impossible, which considerably restricts the functionality of the devices. We investigate here the possibility of developing a new type of all-optical fiber loop storage device. This device consists of a simple nonlinear passive fiber ring resonator synchronously and coherently pumped by a cw mode-locked train of ultrashort pulses. It is well known that this system exhibits rich nonlinear dynamics, in particular, optical bistability which is a feature naturally suited for applications to optical storage. However, erasing the data in an optical bistable element requires to switch off the holding beam and is therefore not practical. Recently, Haelterman et al. [2] have studied the polarization dynamics of nonlinear dispersive ring cavities with cw pump and have shown that these devices exhibit a polarization symmetry breaking characterized by a pitchfork bifurcation. This feature can be applied to the development of a set-reset flip-flop all-optical fiber loop pulsed memory. This work aims at presenting the results of a preliminary investigation of such a storage device.
Optical switches with low crosstalk based on low cost polymer waveguide technology
Authors: Keil N. , Yao H. H. , Zawadzki C.
Published: February 2023

Optical switches are considered to represent attractive components in all-optical networks as, for example, for circuit protection switching to by-pass a faulty system or cable, and in optical cross connects. Switching of cable TV in LANs, of high bit rate data in the optical backplanes of a computer and optical signals in sensors and vehicles (fly-by-wire) may be further applications in the telecommunications, microsystems and automotive area. High performance at low cost may be achieved if polymer waveguide technology is used.
Subpicosecond All-Optical Switching in Thin-Film Fabry Perot Interferometers with Quasi-Zero-Dimensional Intermediate Layers
Authors: Goncharova Olga V.
Published: February 2023

Thin-film semiconductor Fabry-Perot interferometers with nonlinear intermediate layers are of particular interest as components for optical data processing since under certain conditions they can perform optical switching and modulation. The principle of such operations is the sweeping of the cavity transmission (or reflection) peak in response to control pulses. For a high-finesse Fabry-Perot cavity, a small change in the intracavity refractive index can translate into a large change in the cavity reflection and transmission. Optical bistability in thin-film interferometers (TFIs) with semiconductor intermediate layers of ZnS, ZnSe etc., synthesised by thermal deposition and molecular beam epitaxy, have been achieved earlier by a long-wavelength shift of the transmission profile due to the thermo-optic nonlinearity mechanism with microsecond relaxation times [1, 2].
Record performance Near-IR (765 nm) AlAs/AlGaAs VCSELs
Authors: Gulden K.H. , Moser M. , Schweizer H.P. , Epler J.
Published: February 2023

We have fabricated AlAs/AlGaAs Vertical Cavity Surface Emitting Lasers (VCSELs) emitting at 765 nm with record performance. The VCSELs were fabricated using MOVPE and a combination of dry and wet etching for the lateral structuring of the laser posts. Minimum threshold currents of 600 μA and threshold voltages of 1.9 V are achieved for VCSELs with a mesa diameter of 26 μm. The maximum slope efficiencies are 0.46 W/A with wallplug efficiencies of 11.2 % at an output power of 1 mW. The maximum output powers for larger devices exceed 5 mW. To our knowledge these are the best performance characterstics for VCSELs operating in the 760 - 780 nm wavelength range. Compared to recently published data on 780 nm VCSELs in the GalnAsP/AlGalnP material system, the threshold currents ate more than a factor of 4 smaller, the wallpug efficiencies are a factor of 1.7 larger. We attribute the high performance to the accurate control over growth rates and aluminum contents, the layer design and the improved lateral current confinement by an additional lateral selective etching step. Spectral measurements show that the lasers operate single transverse mode over a wide current range with single mode output powers above 1 mW. A comparison with conventional mesa-etched VCSEL structures is made to demonstrate the impact of the additional lateral etching step on the device performance.
The near-field far-field transition in interferometric microscopy: Implications for superresolution approaches
Authors: Totzeck M. , Tiziani H.J.
Published: February 2023

A modified moment-method was developed for the rigorous calculation of 2D-electromagnetic near-fields of arbitrary structures in a stratified medium for obliquely incident, plane waves. These near fields serve as starting point for the calculation of the resulting images according to conventional bright- or darkfield, interferometric or confocal scanning microscopy (Fig. 1).
Optically levitated stylus for scanning force microscopy
Authors: Friese M. E. J. , Rubinsztein-Dunlop H. , Heckenberg N. R.
Published: February 2023

A single-beam optical gradient trap could potentially be used to hold a stylus for scanning force microscopy1. An optically trapped particle can be modelled as a harmonic oscillator and can thus be characterised by its spring constant. We have determined the spring constants for particles trapped in both Gaussian and donut beams2, using a novel technique of measurement of the backscattered light.
Interface Characterization by Second-harmonic Microscopy
Authors: Flörsheimer M. , Bösch M. , Brillert Ch. , Fuchs H.
Published: February 2023

The technique is based on the interface specific generation of second-harmonic (SH) light if the sample is illuminated with high laser intensities. The SH light is used to create a magnified image of the interface structure on the target of an electronic low light-level camera. The response of the camera is calibrated. Hence, the second-order optical susceptibility tensor of any structure resolved in the images can be measured.
Surface feature reconstruction using scanning beams
Authors: Friedmann Michael , Paquet Eric , Shamir Joseph
Published: February 2023

This work presents an alternative to imaging investigation methods for structures with details smaller than the diffraction limit. We describe an optical setup capable of sampling the space and the spatial frequency domain of the target. The spatial information is achieved by monitoring the scanning process, and the frequency data is measured in the far field of the scattered beam.
Holographic Memory and the Problem of Interconnects
Authors: Mikaelian A.L.
Published: February 2023

A holographic memory in parallel information recording and the effect of carrier and interference noises are investigated. Noises are shown to influence the limit data storage density when information is recorded as one-dimentional holograms. A relation between the holographic memory storage capacity and the readout signal/noise ratio is determined. The use of one-dimentional holograms for interconnects in optical neural networks is considered. Another approuch for generating interconnects relies on multiplicators and beamsplitters built around special computer-synthesized HOEs. The fabrication of experimental samples of such elements for the visible spectral range by means of e-beam lithography is reported on. Combined liquid and plasmachemical development was used to provide a required relief depth. The minimum zone width is 300 nm and the maximum depth is 800 nm. Examples of beamsplitters for 630 nm and 530 nm with up to 1000 beams are given. Their possible use as auxiliary elements for making 3D holographic interconnection devices is considered.
GeSb-Based Thin Films for Optical Storage Applications
Authors: Morilla M.C. , Afonso C.N. , Solis J. , Siegel. J.
Published: February 2023

There are several applications of information technologies that can benefit from the large advances achieved in the field of ultrashort pulse generation. These include, among others, optical switching, routing or storage. The need for mass storage media compatible with all-optical information processing schemes using ultrashort laser pulses has lead us to investigate the feasibility of performing reversible phase change optical recording with ultrashort laser pulses. This work reports on the investigation of the optical writing/erasing (W/E) characteristics of Sb-rich GeSb based films with ps laser pulses. The optical contrast, W/E thresholds, amorphizability, amorphous phase stability and transformation time of these phase change media have been determined as a function of several parameters including pulse energy, film composition and thickness, and substrate properties. The write and erase operations are performed in static conditions using 10 ps laser pulses at 583 nm. The laser beam is spatially filtered and focused on the sample surface while the evolution of the reflectivity of the irradiated surface is measured in real time with a resolution of about 1 ns by means of a HeNe probe laser (633 nm). The films are initially either in crystalline or amorphous phase and are irradiated with a single pulse or with two pulses in order to reverse (erasing) the phase transformation induced by the initial (writing) pulse. In some cases, multiple laser pulses were accumulated in order to perform repetitive cycling among the amorphous and crystalline phases.
Four-wave mixing and gain-gratings in laser materials
Authors: Brignon A. , Huignard J.-P.
Published: February 2023

Phase conjugal ion by degenerate four-wave mixing (DTVVM) in saturable gain media is a nonlinear process of major interest for applications to dynamic holography and phase-distortion correction of an optical wave propagating in laser media [1,2,3]. The use of laser amplifiers for such operations presents very attractive features including the automatic matching of the nonlinearity with the laser wavelength, a fast response time and a high efficiency of the nonlinear process due to the laser amplification of all interacting beams. This process is based on the possibility of writing dynamic gain gratings when interfering beams are propagating in a laser medium by gain saturation.
Near infrared pulsed phase conjugation in Cr4+:YAG saturable absorbers
Authors: Brignon A. , Huignard J.-P.
Published: February 2023

Optical phase conjugation via degenerate four-wave mixing (DFWM) in saturable absorbers presents the advantages of being a fast response time and passive technique. What makes this process attractive is also the possibilitv of using solid-state and compact materials [1,2]. Recently, it has been shown that tetravalent chromium (Cr4+) doped GSGG and VSGG can be used for phase conjugation at the fundamental wavelength of neodymium lasers at λ = 1.06 μm [3,4]. In this Communication, we demonstrate a more efficient DFWM process by using Cr4+-doped yttrium aluminium garnet (YAG) at λ = 1.06 μm in the nanosecond regime.
Edge Dislocation of FWM Dynamic Grating in Photo-Refractive Medium
Authors: Khyzniak A. I. , Bougaychouk S. A.
Published: February 2023

Four wave mixing (FWM) (fig. 1) in photorefractive material (FRM) is being studied intensively [1]. One of interesting mode is double phase conjugate mirror (DPCM), when beams (1) and (4) are absent in their inputs. It is possible to have FWM incoherent beams (3) and (2) [1]. For this case fig.2 shows the variation intensity of all interaction beams (1,2,3,4) across the slab of FRM, The dynamic grating has plane iso­phase surfaces and variable amplitude (curve 5 on fig.2).
CW Laser Performance of Yb-doped KY(WO4)2 and KGd(WO4)2
Authors: Kuleshov N.V. , Lagatsky A.A. , Sheherbilsky V.G. , Mikhailov V.P. , Heumann E. , Jensen T. , Dienning A. , Huber G.
Published: February 2023

Yb-doped materials attract interest as promising active media for 1 μm all-solid-slate infrared lasers pumped by InGaAs laser diodes. In the present paper we report, for the first time to our knowledge, room-temperature cw laser performance of two Yb3+-doped crystals KY(WO4)2 (KYW) and KGd(WO4)2 (KGW) under Ti-sapphire and diode laser pumping.
Mid-Infrared Diode Lasers Based on III-V Alloys for the Spectral Range 3-4 µm
Authors: Yakovlev Yury P.
Published: February 2023

The main applications of mid-infrared diode lasers are high-resolution molecular spectroscopy and gas pollutant detection. III-V semiconductor lasers based on InAs alloys are of great interest for the spectral range 3-4 µm. However, there are some reasons limiting high temperature operation of III-V mid-infrared lasers. Main of them is non-radiative Auger-recombination that influence strongly temperature dependence of threshold current, especially in narrow-gap semiconductors. Last year some novel physical approaches have been proposed to overcome Auger-recombination problem including non-traditional structures (type II superlattices, quantum cascade laser).
Optically pumped mid-infrared intersubband emission and lasing in coupled quantum wells
Authors: Sa’ar A , Lavon Y , Julien F. H. , Moussa Z , Wang J. , Leburton J -P , Planel R
Published: February 2023

Mid infrared semiconductor lasers that are based on population inversion between conduction subbands of a quantum well (QW) structure have attracted much attention recently. Faist el al [1] demonstrated the operation of the quantum cascade laser which is a unipolar intersubband injection laser Another scheme to generate population inversion between conduction subbands is by optical pumping [2], In this contribution we summarize our recent experimental and theoretical results including the observation of mid-infrared emission from a GaAs/AlGaAs coupled QWs (CQW) structure [3-4] (see Fig. 1).
Optical gain in ZnCdSe-ZnSe quantum well structures
Authors: Rees P. , Heffernan J.F. , Logue F.P. , Donegan J.F. , Jordan C. , Hegarty J. , Taniguchi S. , Hino T. , Hiei F. , Ishibashi A.
Published: February 2023

ZnSe-ZnCdSe quantum well structures are the most likely candidate for the fabrication of commercial blue-green semiconductor lasers. Devices incorporating these wells have achieved room temperature cw lasing at 510nm with operating lifetimes of up to 100 hours. In wide band gap semiconductors the increased binding energy and higher effective masses cause an increase in the Coulomb enhancement of the recombination rate and a decrease in the scattering lifetime of the carriers. The dependence of the optical matrix element on the inverse of the energy gap also means that the available gain in wide band gap materials is significantly lower than in narrow band gap semiconductors. Therefore the prediction of a wide band gap semiconductor light emitting device’s performance is not simply an extrapolation from that of a device incorporating narrow band gap III-V materials.
Laser Induced Structure Modification on Ceramics
Authors: Nicolas G. , Langlade C. , Autric M.
Published: February 2023

Using a UV laser radiation focused on a ceramic material, many transformations occurs on the irradiated area and in depth. These laser induced transformations are of crystallographic, mechanical and chemical origins.
Quantifying CO2 and Nd:YAG laser cleaning of polluted blonde sandstone
Authors: Tiedemann Jörg , Watson Ian A
Published: February 2023

Laser renovation is still a rather new field of study, and on most occasions reasonable results have to be obtained by “trial and error” The reason for this is the difficulty in handling the vast amount of parameters associated with the degree of pollution, type of stone and the laser. There is still a lack of measuring techniques to indicate how much of the pollution has been ablated (state assessment) and, in particular, how much of the pollution is being ablated during the cleaning process (process monitoring). The aim of this work, therefore, was to find a way to quantify the ablation process in-line.
Photonic Integrated Transceivers for Low Cost and High-End Applications within Bidirectional Optical Communication Systems
Authors: Kaiser R. , Hamacher M. , Heidrich H. , Löffler R. , Malchow S. , Rehbein W. , Schroeter-Janßen H. , Steingrüber R.
Published: February 2023

Full duplex transceivers, which transmit and receive optical signals at different wavelengths/frequencies, are key components within todays and future high capacity bidirectional optical communication systems (e.g. local acces networks, computer data links, measurement and control systems). For those commercial applications they have to meet several specifications and requirements, for example fabrication at low cost, high temperature stability, very low electrical and optical near-end crosstalk levels, low power consumption, high compactness and robustness, and good reliability.
Conjugated Resonators and the Problem of Transverse Pattern Controlling
Authors: Lyubimov V.V.
Published: February 2023

Conjugated resonators are best suited for the transverse pattern controlling because their modes are practically degenerated in frequency and losses. The minimum controlling action is defined by the eigenvalue spectrum splitting. The method of action is defined by the losses minimization condition for given transverse pattern and by the requirements to its stability. The controlling spatial light modulators characteristics impact on the modes and sensitivity to active medium optical inhomogeneity and to the precision of resonator components fabrication is investigated. The conjugated resonator schemes that provide reduction of the radiation load on the controlling spatial light modulators are discussed.
Potential and Future Aspects of Laser Beam Welding
Authors: Sepold G.
Published: February 2023

The main factors influencing the potential of laser beam welding are defined by the product, the quality of the welded component and the available laser system. At the beginning of the production chain stands the laser oriented design. Using conventional design guidelines will not allow to achieve the full benefit of laser beam welding. The need for laser oriented design will be shown e.g. for the substitution of riveting by User beam welding in the aircraft industry [1]. An other example is the substitution of MAG-welding technology by laser beam welding in the ship building industry.
On-line quality visualization on thin metal laser-Cutting
Authors: Hutflesz Georg , Bohrer Markus , Schuöcker Dieter
Published: February 2023

There still exist permanent problems in obtaining high quality laser cuts on thin metal sheets, when producing small and delicate geometric structures. It is of great interest to get a reliable diagnosis about the quality of the cutting curve. We use two sensors of different spectral sensitivity, on the one hand to observe the intensity, on the other to compute temperature of the process. Correlation between the on-line calculated optical signals and the varying cutting quality is shown.
Lossless beam-cleaning for linear CO2 waveguide laser arrays
Authors: Lapucci A. , Lescroart G. , Bourdet G. L.
Published: February 2023

The undesired side lobes in the far field emission of a linear array of phase coupled lasers can be reduced by using a single phase correcting mirror outside the laser array cavity [1]. Even in that case the beam has strong asymmetry and astigmatism, that can be corrected by an off-axis spherical mirror We show the beam obtained experimentally with this kind of correction The global optical set-up consists in three reflective optical elements producing a lossless transformation of the field distribution from a periodic repetition of small highly divergent sources to a quasi-gaussian symmetric beam.
Method of statistical simulation of laser energy storage
Authors: Denisov V.I.
Published: February 2023

In this work the method of statistical simulation allowing to calculate an interaction of a laser pulse with nonlinear absorbing many-level medium when the time duration of the pulse is equal to longitudinal characteristic relaxation time has been suggested and realized. The two problems were solved by this method. The first problem was the one of laser energy storage on the metastable level of the medium atoms. The space and time characteristics of this inverted medium of plane geometry were calculated. The amplification coefficient of forbidden transition versus different parameters of this problem was obtained. Using Asl as an example the mechanism of two-step photoionization of atoms and mechanism of formation of inversion of the population between a metastable level and a ground state (mechanism of accumulation of laser radiation energy in volume) are investigated. It is shown that due to the "imprisonment" (trapping) of reemited photons leads to the sharp decrease both of the length of interaction between laser radiation and medium, and the length of accumulation of laser radiation energy in volume. In this case the gain factor of inverted medium is one order of magnitude less than that obtained by theoretical estimates (neglecting this effect). The algorithm suggested allows solving these problems within multi-pulse mode taking into account the collision and diffusion processes.