bluuebunny/crossref_metadata_2025 huggingface dataset:
High repetition rate intracavity optical parametric oscillator
Authors: Victori S. , Dubois A. , Lépine T. , Georges P. , Brun A.
Published: February 2023

Optical parametric oscillators (OPO) are of particular interest to produce tunable coherent radiations, especially in the near infrared where no efficient solid state lasers are available. Usually, the OPO and the pump laser are separate oscillators (extracavity configuration). Another alternative is to place the OPO cavity inside the laser cavity to obtain an intracavity optical parametric oscillator (IOPO). This idea, proposed in the beginning of the 70s, has led to only a few recent experimental studies [1]. The advantage to place the OPO inside the laser cavity is to benefit of the fluence inside this cavity larger than the fluence available outside.
Investigation of the tuning behaviour of a single-frequency Tm:YAG laser with external feedback
Authors: Dicks B.-M. , Diening A. , Heumann E. , Huber G.
Published: February 2023

The 3F4 → 3H6 ground state transition of the Tm3− ion leading to eyesafe laser emission around 2 μm is interesting for a variety of applications. Of special interest for Doppler-LIDAR applications is a high-power pulsed single-frequency laser tunable to wavelengths with high atmospheric transmission (e.g. at 2021.8 nm). This can be achieved using a stable cw single­frequency oscillator of the required wavelength as a seed laser for a high-power Q-switched amplifier.
Characterization of dispersion managed solitons for small energy
Authors: Cautaerts Vincent
Published: February 2023

By using an appropriate scheme of dispersion in a fiber, the so-called dispersion-managed pulses have been shown to exist in the non-linear regime of propagation [1]. The use of alternatively positive and negative dispersion fibers leads to the propagation of a breathing pulse, which seems to present a lot of advantages, like a higher energy, reduced modulational instability, smaller jitter caused by collisions between signals, reduced Gordon-Haus effect….
Demonstration of time division demultiplexing from 40Gb/s to 10Gb/s via polarisation switching in a semiconductor optical amplifier
Authors: Stephens MFC , Kelly AE , Nesset D , Wonfor A , Penty RV
Published: February 2023

There has been much recent interest in the use of semiconductor optical amplifiers (SOAs) as ultrafast (40Gb/s and higher) nonlinear switching elements. In particular, SOAs have been employed as wavelength conversion devices for use in wavelength division multiplexing networks and as optical time division de/multiplexing (OTDM) elements such as that reported by Patrick et. al [1]. Here we demonstrate for the first time we believe, a polarisation switching technique in which a 40Gb/s OTDM signal is optically gated by a 10GHz pulse train, affording high extinction ratio, error free demultiplexing from 40Gb/s to 10Gb/s.
Low Noise Avalanche Photodetectors
Authors: Li K.F. , Ong D.S. , David J.P.R. , Tozer R.C. , Rees G.J. , Button C.C. , Robson P.N.
Published: February 2023

Avalanche photodetectors (APDs) for 1.0 to 1.6μm wavelengths are known to be more sensitive than p-i-n photodiodes because of the internal multiplication provided by impact ionisation. However the multiplication process also produces avalanche noise which impairs the signal to noise ratio and limits sensitivity at high values of multiplication. The widely used theory of McIntyre[1] shows that the excess noise factor, F, falls for a small (≪1) ratio of ionisation coefficients k=β/α, where α is the ionisation coefficient of the initiating carrier.
Continuous-wave, singly-resonant optical parametric oscillator based on periodically poled RbTiOAsC4
Authors: Edwards T.J. , Turnbull G.A. , Dunn M.H. , Ebrahimzadeh M. , Karlsson H. , Arvidsson G. , Laurell F.
Published: February 2023

The advent of periodically poled nonlinear materials offering high deff and the flexibility of grating-engineered phase-matching has had a broad impact in the field of nonlinear optics. In particular, the development of periodically poled (PP) LiNbO3 (PPLN) has placed the once prohibitively high oscillation thresholds of externally pumped singly-resonant optical parametric oscillators (OPOs) within the domain of conventional watt-level laser pump sources [1]. To reach oscillation threshold however, these devices need relatively long interaction lengths; when coupled with small crystal apertures and thermal lensing problems in PPLN these criteria can become limiting factors for high power operation. Intracavity cw OPOs have recently offered an alternitive solution for efficiently generating high-power, narrow-linewidth tunable cw radiation in the near-infrared [2]. The intracavity approach is uniquely placed to take advantage of smaller interaction lengths and lower d
eff
of recently developed periodically poled (PP) nonlinear materials such as PP-KTiOPO4 (PPKTP) and PP-RbTiOAsO4 (PPRTA). Combined with a static pump tuned geometry and room-temperature operation, intracavity SROs offer a versatile approach for generating cw laser radiation from these new quasi-phase-matched nonlinear materials. Here we outline the performance characteristics of a Ti:sapphire (TIS) pumped cw intracavity singly-resonant optical parametric oscillator (SRO) based on a 4.5-mm-long PPRTA crystal. To our knowledge, this is the first report of a cw OPO based on PPRTA.
Second-Harmonic Generation in HgGa2S4
Authors: Takaoka E. , Kato K.
Published: February 2023

This paper reports what is believed to be the first attainment of tunable SHG in HgGa2S41,2. The HgGa2S4 crystal used in this experiment was 8 × 8 × 8 mm3 and fabricated at θ = 67.5° (θ = 22.5°) and ϕ = 0° with polished four side surfaces. The transmission range is 0.55 – 12.4 μm.
Optical Waveguide Chemical Sensors Using Grating Coupling
Authors: Doyle Aidan , MacCraith Brian D.
Published: February 2023

There is an increasing need for reliable, repeatable gas/aqueous phase chemical sensors in many industrial, medical and environmental applications. Much work at present is being done in the area of sol-gel sensing and more specifically planar waveguide based chemical sensors. This form of chemical sensor utilises evanescent wave sensing. One of the key issues in this configuration is the coupling mechanism into the waveguide. Many groups have reported the fabrication of sensor platforms, which contain low loss planar waveguides along with a variety of techniques. Prism coupling is a popular mechanism for launching light into a waveguide. However, bulky optics and precise beam alignment can lead to lack of repeatability. Another mechanism commonly used to launch light into a waveguide is grating coupling. Many different fabrication processes are used to produce grating couplers on the surface of waveguides. The technique used in this work was the embossing procedure.
Polarization-Independent Double Phase Conjugate Mirror
Authors: Dupray V. , Brunel M. , Özkul C. , Wolffer N. , Gravey P.
Published: February 2023

Double Phase Conjugate Minors (DPCM) are of great interest for the realization of free-space interconnections between single mode optical fibers. However, an alteration of the polarization of the incident beams, which can be easily induced by mechanical constraints on standard fibers, leads to a dramatic reduction of the conjugation efficiency. We present here a polarization-independent DPCM. The polarization insensitive experimental set-up is described in figure 1. A biréfringent calcite crystal is inserted at the output of the monomode fiber. Thus, two orthogonally polarized components are spatially separated. The polarization of the component that would not contribute to the formation of the DPCM in a conventional configuration is rotated in a liquid crystal cell. Both components are then directed into the InP:Fe sample with a lens. The pump beam results from the interference of the two components. Our experiment is performed by manipulating the polarization of only one pump beam to demonstrate the principle of the polarization independent DPCM. Obviously, the other pump beam could be obtained applying the same method. In order to eliminate conical diffraction and instabilities, this elementary set-up was incorporated in a 2Z-DPCM configuration. Experiments were carried out with an InP:Fe photorefractive crystal at the telecommunication wavelength of 1.32 μm. The diffraction efficiency and the depletion rate were measured for different polarization directions of the incident beam labeled A. The results are illustrated in figure 2. The averaged values of the depletion rate and the diffraction efficiency are 50% and 10% respectively. It is worth noting that these results are comparable to those obtained with a classical configuration. The relative variations of the diffraction efficiency are less than 8% when the polarization state of the incident beam varies. Keeping in mind that the relative variations can reach nearly 100% in a conventional DPCM, our device can be considered stable.
Conditions for efficient build-up of power in a ring-cavity with Rh:BaTiO3
Authors: Kaczmarek Malgosia , Eason Robert W.
Published: February 2023

Numerous interaction geometries have been developed for photorefractive materials that rely on amplification of light via the two-beam coupling effect. One of the most elegant and simple configurations is a unidirectional ring resonator, which consists of a photorefractive crystal placed in a ring cavity and pumped by an external beam [1]. If the two-beam coupling gain is above threshold, the resonating beam will build up from the amplification of scattered light.
Real time holography and phase conjugation in films of azo dye containing side-chain LC polymers
Authors: Larichev A. V. , Simonov A. N. , Shibaev V. P.
Published: February 2023

Progress in the field of optical data processing and storage depends in great extent on development of the new effective nonlinear media [1]. Azo dye containing side-chain LC polymers are thought to be one of the perspective candidates for different optical applications because of their chemical stability and high nonlinear susceptibilities [2]. An attractive feature is the combination of liquid crystalline (LC) properties and optical nonlinear properties originating from light induced trans-cis isomerization of chromophores. The substance may be attributed to a class of two component nonlinear systems with vigorous intermolecular interaction. Behaviour of mesogenic (matrix) and dye subsystems are strongly correlated via the internal field. Thus, acting on the mesogenic subsystem by applying electric field and heating, it is possible to control the process of photo induced anisotropy formation in the polymeric bulk. However, the influence of the mentioned factors on the performance of the media in optical information systems is not clear yet.
A 7-fs Ti:sapphire laser focusable to 5 × 1013 W/cm2
Authors: Poppe A. , Xu L. , Fürbach A. , Lenzner M. , Krausz F. , Spielmann Ch.
Published: February 2023

Femtosecond light pulses are important tools for time-resolved spectroscopy and nonlinear optics owing to their ultrashort duration and high peak power, respectively. However, intensities in excess of 1012 W/cm2 have not been demonstrated with these systems, limiting their utility for nonlinear optics. In this contribution we demonstrate that recent innovations in sub-10fs laser technology now allow generating i) sub-10fs optical pulses with a peak power of 1.5 MW and ii) intensities greater than 5 × 1013 W/cm2, a never- before-accessed range at repetition rates of a≈ 100 MHz. This performance is achieved with a compact all-solid-state system and opens up the way towards the investigation and possible exploitation of nonperturbative nonlinear optical processes at repetition rates of around 100 MHz for the first time.
Spectral Imaging of Pulse Temporal Profile
Authors: Mouradian L. , Zohrabyan A. , Froehly C. , Louradour F. , Barthelemy A.
Published: February 2023

We present a new technique for measuring pulse temporal profiles at the pico- and femtosecond time scales using a direct real-time method based on the nonlinear- optic Fourier transformation process (NOFT). NOFT is implemented in the spectral compressor, which consists of a dispersive delay line followed by a nonlinear single-mode lightguide [1]. In DDL pulses are stretched experiencing a negative chirp, and in the nonlinear fiber the chirp quenching due to self- or cross- phase modulation (SPM/XPM) leads to spectral narrowing. The accurate chirp quenching results in NOFT: the conversion of temporal information to the spectral domain for both the intensity and the phase of the input wave. So, spectral compressor with a spectrometer can serve as a high temporal resolution optical oscilloscope, and the problem of direct, real-time, high-resolution temporal measurements is reduced to standard spectrometry.
Tracing the phase distortion of a single femtosecond light pulse
Authors: Kabelka V. , Masalov A. V. , Nikitin S. , Milchberg H.
Published: February 2023

A frequency tracer (FT) based on noncollinear second harmonic generation autocorrelator for two-dimensional time-frequency imaging of a single femtosecond light pulse without using a spectral apparatus [1] had implemented for a first time. An experimental test of frequency tracer has been performed by measuring the instantaneous frequency of femtosecond pulses produced by a chirped pulse amplification Ti:sapphire laser system. In a normal operation the system is able to produce pulses up to 1.5 mJ energy and about 90 fs duration FWHM. The frequency traces were collected for pulses at different compressor grating separations. Experimental data on the linear chirp and pulse duration have been checked against a simple model, where the shape of the gausian pulse changes due to propagation through a dispersive path between pair of diffraction grating in a compressor. Detuning of the grating separation from its optimal value results in quadratic (in terms of frequency) phase shift of spectral components of output pulse. The data on chirp and pulse duration versus grating separation are in a good agreement with the estimations of dispersions at the system output. The registered images shown not only linear chirp of pulses (which was measured unambiguously) but also the fourth order phase distortion (cubic chirp). We prove by numerical calculations that images produced by the frequency tracer have simple intuitive meaning: the frequency trace is formed by maxima of two-dimensional image and does not require any iterative retrieval algorithm for visualising the phase distortions [2]. The calculations show that the second-harmonic frequency tracer allows to measure the even-order phase distortions of femtosecond light pulses: chirp, fourth-order, etc. These distortions include the phase self-modulation (Kerr-nonlinear contribution) of symmetric pulse.
Laser Surface Modifications
Authors: Hügel Helmut
Published: February 2023

Any machine parts, tools construction components and workpieces do interact via their surfaces with each other respectively with their environments. Depending on the application field and the task, the interaction occurs on the basis of mechanisms that can be of mechanical, chemical, electrical or optical nature or of several of these. In any case, the property of the surfaces is an essential feature with respect to the functionality of the particular element. In general, the requirements are met by materials that are not necessarily, at the same time well-suited for the piece in its entirety, be it for reasons of design, processing technologies, costs or others. Against this background, modern production approaches rely on a great variety of adequate and well developed surface technologies.
Producing high quality dies using CO2-lasers and a new designed engraving machine
Authors: Penz A. , Fazeny S. , Schuöcker D.
Published: February 2023

The big advantage of the laser ablation process is the flexible computer assisted manufacturing of three dimensional structures in different materials, preferably steel. For an economic production several preconditions have to be met. Firstly the process should be very accurate so that high quality surfaces have to be obtained.
Beam Reformatting of CO2 Array Lasers
Authors: Villarreal F , Abram R , Jones D R , Baker H J , Hall D R
Published: February 2023

Industrial laser applications often require beam shapes other than the usual bell shaped profile generated directly by conventional lasers. An example is surface treatment processes such as cladding or annealing which benefit from a uniform flat top profile. Traditionally, a multi-faceted beam homogeniser mirror is used to transform the output of a good-beam-quality laser, but this is a relatively expensive component and the spatial coherence of the initial beam produces significant speckle or fringe patterns.
Passively Q-Switched Microchip Lasers and Applications
Authors: Zayhowski J. J.
Published: February 2023

Diode-pumped passively Q-switched Nd:YAG microchip lasers are compact, economical, all-solid-state sources of coherent, subnanosecond, multikilowatt pulses at high repetition rates, with applications in diverse areas.
Single- and double-frequency, thin-film tuned, and stabilized, diode-pumped Nd:crystals lasers
Authors: Jabczynski J. , Peshko I.
Published: February 2023

In laser radar system a tunable single- or double-frequency oscillator with frequency chirping is required. For metrology purpose the frequency and amplitude stabilized laser is necessary. To achieve the driven frequency parameters and high output power we have designed the diode-pumped Nd:YVO4, Nd:YAG, and Nd:YLF lasers. The metallic thin-film absorbing selector has been used to provide simultaneously single- or double-frequency operation, wave length tuning, frequency chirping or amplitude and frequency stabilization of the laser output.
Imaging in turbid media by a new method based on a selective feedback in a microchip Laser
Authors: Lacot Eric , Stoeckel Frédéric
Published: February 2023

Imaging of biological tissues1 provides important information for diagnosis. Several techniques have been developed like homodyne scanning confocal microscopy2, heterodyne laser microscopy, optical coherence tomography or time resolved experiments including time resolved holography. Techniques based on imaging with ballistic photons are limited by the rapid decrease of the intensity retrodiffused when the depth increases and are usually limited to a few millimeters for biological tissues.
Dynamic Holograms on Polarization Gratings in a Ferroelectric Liquid Crystal
Authors: Galstyan T.V. , Saad B. , Dinescu L. , Lemieux R.P.
Published: February 2023

We report a new mechanism for dynamic hologram (DH) formation based on the photoinduced increase of spontaneous polarization (Ps) in a ferroelectric liquid crystal (FLC) doped with a chiral thioindigo dye [1], The application of a DC electric field (without light irradiation) produced a switch of the Ps of our cell. A subsequent decrease of the voltage brought the system back to its initial state while demonstrating a significant hysteresis behavior. The experiment was repeated with the sample cell under spatially uniform irradiation at 514.5 nm. This caused the hysteresis region to shift to lower voltages. We used this effect to produce electric field controlled DH by generating gratings of Ps in the presence of a DC electric field.
Novel all-optical light transmission modulator with piezoelectric barriers
Authors: Ortiz V. , Pelekanos N.T. , Mula Guido
Published: February 2023

Fast parallel image processing applications require optical modulators that are sufficiently fast (MHz modulation rates [1]) and that can operate with the optical power of a standard laser diode (W/cm2). We present here results obtained with innovative-design heterostructures, based on piezoelectric barriers, suitable for realising all-optical modulators that match these requirements.
Fast transient response of light deflectors based on periodically poled LiNbO3
Authors: Gnewuch H. , Pannell C.N. , Ross G.W. , Smith P.J.R. , Geiger H.
Published: February 2023

Recently, integrated-optical elements, such as lenses, prisms, and gratings, have been demonstrated by domain-inversion in thin Lithium Niobate wafers and by applying a homogeneous electric field between the planar surface electrodes, see e.g. [1]. However, to the best of our knowledge, so far only the static response of these electro-optic (EO) devices has been characterized. We report on the transient response of a light deflector based on a poled grating in LiNbO3.
Excimer Laser Implantation of Pyrene Molecules In A Solid Polymer
Authors: Karnakis D. M. , Ichinose N. , Kawanishi S. , Fukumura H.
Published: February 2023

Laser ablation of polymers doped with aromatic molecules has been studied extensively over the past decade [1]. Based on these studies, a new phenomenon has emerged termed Laser Molecular Implantation (LMI) which involves the transfer of intact molecules between polymer films irradiated with low intensity laser light [2].
Pulse laser removal of sputtered oxide films: measurement of adhesion strength
Authors: Oltra R. , Sartori C. , Boquillon J.P.
Published: February 2023

Heating power of continuous lasers (CO2) has been demonstrated to motivate the spall of coatings by generating compressive stress in the coating1. On the other hand, dynamic spallation of coatings can be checked by using pulsed lasers, as shown in the pionnering work presented by Vossen2. Quantitative modelling of this laser spallation technique was performed by V. Gupta allowing to determine the interface strength of several metal-ceramic interfaces3. The same approach has been used by M.W. Sigrist for plasma sprayed ceramic coatings4.
Surface Morphology of Laser Superheated Pb(111) and Pb(100)
Authors: Elsayed-Ali H. E. , Zhang Z. H. , Lin Bo , Zeng X. L.
Published: February 2023

Superheating of solids is rarely observed due to the presence of a thin disordered surface layer formed below the melting point, Tm, which provides a nucleation site for melting. Premelting is particularly evident in open surfaces. While Pb(110) disorders at a temperature as low as 150 K below Tm = 600.7 K, Pb(111) remains ordered up to Tm - 0.05 K. [1]. Some surfaces that do not premelt can superheat under certain conditions [2-4], Superheating of Pb(111) and Bi(0001), and some superheating of Pb(100) by ~180 ps laser pulses was observed in time-resolved high-energy electron diffraction (RHEED) experiments [2-4], The Pb(111) and Bi(0001) surfaces superheat up to ~120 K and ~90 K above Tm of Pb and Bi, respectively. Evidence of residual order on Pb(100) up to ~15 K above Tm was also observed [3], Molecular dynamics simulations of surface melting of several fee metals showed a good agreement with the experimentally observed superheating of Pb(111) [5], One simulation showed that cooperative movement of the superheated surface atoms results in the filling of vacancies and the surface becomes atomically flat by a superheating surface repair process [5], This annealing mechanism was attributed to the high vibrational amplitudes which atoms are forced into by the ultrafast superheating pulse.
High-Power Single Frequency Tunable Ultraviolet Laser
Authors: Robertson G. , Bente E.
Published: February 2023

The generation of tunable ultraviolet light can be achieved by direct laser action in the ultraviolet or by frequency conversion from the infrared1. To achieve tunable output from an all solid state device at several kHz repetition rate and output powers in the order of one Watt or more, it is necessary to consider Ti:sapphire as the laser medium and frequency double its output. Doubling of the wavelength from 700 to 800 nm with reasonable efficiency is problematic due to the limited selection of non-linear materials. LBO and BBO are typically the materials of choice. The optimum solution depending on the peak pump power available.
Feedback Control Of The Intensity Noise Of Injection Locked Lasers
Authors: Huntington E. H. , Buehler B. C. , Harb C. C. , Ralph T. C. , Bachor H.-A. , McClelland D. E.
Published: February 2023

Injection locking has been demonstrated to be a very effective method of intensity noise suppression [1]. However, the intensity noise of an injection locked laser at low frequencies is dominated by noise due to its pump source and, as such, is relatively unaffected by the process of injection locking. Also, at frequencies near the slave laser’s resonant relaxation oscillation (RRO), the injection locked laser amplifies the intensity noise of the master laser. In this work we will demonstrate an intensity noise suppression system that corrects both of these problems whilst also taking advantage of the benefits associated with using an injection locked laser.
Temperature dependence of 1.55μm VCSELs
Authors: Masum J. , Ramoo D. , Balkan N. , Adams M. J.
Published: February 2023

Recent progress in 1.55μm VCSELs using either wafer-fused or epitaxial mirrors has prompted renewed interest in the temperature sensitivity of these devices. Here we model transitions between parabolic bands with and without k-selection, as well as transitions between the first sub-bands in quantum wells without k-selection. The underlying temperature dependence of the cavity resonant photon energy and the bandgap of the semiconductor are found from experimental data, as illustrated in Fig. 1. This also shows the temperature dependence of the photon energy corresponding to the gain peak, as calculated for the case of no k-selection in bulk InGaAsP. Fig.2 plots the corresponding variation of threshold carrier density, nth, assuming charge neutrality. It is clear that the temperature, Tmin, of minimum nth is somewhat lower than the temperature, Tmatch, at which the photon energy of the gain peak matches that of the cavity resonance. This difference is significant because the conventional approach to VCSEL design has been to assume Tmatch determines the optimum operating temperature, whereas the calculations presented here demonstrate that this could lead to non-optimal performance. The difference between Tmin and Tmatch depends to some extent on the model used, and the cases with and without k-selection in bulk and SQW (no k-selection) material are plotted in Fig. 3.
Mode-Controlled Vertical Cavity Surface Emitting Lasers for Bandwidth Enhancement of Multimode Fibre Links.
Authors: Webster M , Sargent LJ , Dowd P , Heard PJ , White IH , Penty RV , Tan MRT , Cunningham DG
Published: February 2023

There is considerable interest currently in low cost computer interconnects operating at rates of over 1 Gb/s using multimode fibre (MMF). With this fibre being currently the dominant type installed in buildings, transmission distances are limited at these rates. Recently, however, a technique whereby light is injected into the fibre at an offset position has been reported overcoming this limit. Enhancement of the fibre bandwidth by up to a factor of four has been obtained by restricting the set of modes excited within the fibre [1]. It would be preferable, however, if a laser source was available which directly generated locked offset beams for this application.
Monolithic Integration of Vertical Cavity Surface Emitting Laser and Diffractive Optical Element for Advanced Beam Shaping
Authors: Martinsson Hans , Bengtsson Jörgen , Ghisoni Marco , Larsson Anders
Published: February 2023

In recent years, the demand for low-cost high-performance optical interconnect components has increased. One solution has been found with the development of the vertical cavity surface emitting laser (VCSEL) [1]. The VCSEL has a number of attractive characteristics for interconnects such as low operating voltage and current, low divergence circular beam, and the possibility of on-wafer testing and flip-chip mounting. While simple beam shaping can be accomplished using refractive optics, monolithically or in hybrid, more complex beam shaping such as combined beam splitting and focusing for optical fan-out can only be accomplished using diffractive optical elements (DOEs) [2]. Ideally, the DOE should be monolithically integrated with the VCSEL.
A Hot Electron Surface emitting Laser: HELLISH
Authors: O'Brien A , Sceats R. , Potter R. , Poolton N. , Masum J. , Boland-Thoms A. , Balkan N. , Adams M.
Published: February 2023

HELLISH (Hot Electron Light Emission and Lasing in Semiconductor Heterostructure) is a novel longitudinal transport device. This has been researched extensively resulting in two main types of devices; HELLISH-1 and 2.1,2 HELLISH-1 consists of a 130Å GaAs SQW situated on the n-side of an AlGaAs p-n junction within the depletion region. Light emission is from the device surface, independent of the applied electric field and therefore exhibits an XOR function with respect to the applied voltage. Recently, a VCSEL device has been realised by incorporating an upper and lower DBR to the original structure. To date this is the first demonstration of a hot electron based VCSEL at room temperature. As shown in the key of Figure 1, HELLISH-1 forms the cavity of the VCSEL. The lower DBR has 27 periods of AlGaAs layers with varying Al concentration and provides a reflectivity better than 99%. The upper DBR has 17 periods which allows an output from the top surface in the form of lasing.
Assessment of the total emission of sulphur dioxide from Italian volcanoes in simultaneous shipborne measurements using lidar, doas and correlation spectroscopy
Authors: Weibring P. , Lindström T. , Edner H. , Svanberg S. , Caltabiano T. , Cecchi G. , Pantani L.
Published: February 2023

Volcanoes contribute substantial amounts of sulphur dioxide to the global atmosphere, and thus reliable measurements are needed for an accurate assessment of the relative roles of natural and antropogenic emissions. Normally, gas correlation measurements based on COSPEC instruments are performed, observing in ground-based traverses the spectral imprint of the gas in the spectrum of the down-welling ambient radiation. However, because of complicated scattering conditions above, within and below the volcanic plume, data are complex. The differential optical absorption spectroscopy (doas) technique works in a similar way but also provides the full spectrum for detailed analysis. The lidar technique, being an active remote sensing technique, provides more well-defined measurement conditions. Field tests have been performed using the research vessel "Urania", where scans under the plumes from the Italian volcanoes Etna, Stromboli and Volcano were performed. Three cruises were made, where the last one, in August 1997, provided the most complete and accurate data.
Generation of 200-fs Fourier-Transform-Limited Optical Pulses at 1550 nm from Super-Continuum Obtained by a Mode-Locked Semiconductor Laser
Authors: Futami Fumio , Kikuchi Kazuro
Published: February 2023

Recently, we have succeeded in generating the very flat super-continuum (SC) spectrum wider than 200 nm centered at 1550 nm by using a dispersion-flattened fiber having a small normal group-velocity dispersion (GVD) [1]. Since such SC pulse has linear up-chirp across the entire pulse width, we may compress the pulse width to its Fourier-transform-limited (TL) value by using an appropriate amount of anomalous GVD.
Single supermode harmonically modelocked Ti:Er:LiNbO3 waveguide laser
Authors: Wessel R. , Rochhausen K. , Suche H. , Sohler W.
Published: February 2023

Harmonically modelocked lasers are interesting sources for high bit rate optical transmitters. We have already demonstrated actively modelocked Ti:Er:LiNbO3 waveguide lasers with pulse repetition frequencies up to 10 GHz [1]. But, harmonically modelocked lasers usually emit more than one comb of longitudinal modes (so called supermode) causing high frequency noise. For fibre lasers with a large number of supermodes an intracavity Fabry-Perot filter with a high finesse (>50) has been successfully used to select one supermode [2,3]. In this contribution we report single supermode operation of a Ti:Er:LiNbO3 waveguide laser by coupling of the active laser cavity to a passive, low finesse (2.3) waveguide Fabry-Perot.
Mirror-Free, High Power (~140mW) Diode-Pumped 2.7 µm CW Fiber Laser
Authors: Zhao X. , Srinivasan B. , Pulaski P. , Gupta S. , Jain R.K.
Published: February 2023

Because of the strong water absorption near 3 µm in tissue and the consequent ultrashort penetration depths (of a few microns), compact high power (100 mW to 1 W) 2.7 µm laser sources with tem00 beam quality have several important applications in ultrafine intra-ocular and endoscopic laser surgery including transmyocardial revascularization and other intra-arterial procedures1. In such applications, laser energy absorbed by the targeted tissue is capable of its coagulation or precise ablation with minimal damage to the remaining tissue. Other applications that could benefit from compact and efficient sources of mid-IR radiation include infrared countermeasures and spectroscopic sensing.
Emission dynamics of a (GaIn)(NAs) vertical-cavity surface-emitting laser
Authors: Ellmers C. , Höhnsdorf F. , Koch J. , Agert C. , Hofmann M. , Hühle W. W. , Stolz W.
Published: February 2023

Vertical-cavity surface-emitting lasers (VCSELs) are interesting devices for applications in high speed optical fiber networks. Therefore the development of VCSEL structures for the generation of short optical pulses at emission wavelengths in the optical-fiber windows of 1.3 or 1.55 µm is important. The InGaAsP-InP material system which is most common for edge emitters in this long wavelength regime suffers from the lack of epitaxial layers with high refractive index difference. Thus an appropriate distributed Bragg Reflector (DBR) can only be obtained with a large number of mirror layers. This involves not only a high resistance in electrically pumped devices, but also increases the effective cavity length which results in slower dynamics, due to longer photon lifetimes. In contrast, GaInNAs has been demonstrated recently as a very attractive active material for the long wavelength regime. It can be grown lattice matched on GaAs and thus allows to use well established GaAs-AlAs DBRs. We have realized a microcavity laser with GaInNAs quantum wells with a high enough content of nitrogen to reach wavelengths near 1.28 µm. Here we present first results on the picosecond dynamics of a GaInNAs VCSEL-structure.
High Speed 1300 nm Vertical Cavity Surface Emitting Laser
Authors: Peters F.H. , Jayaraman V. , MacDougal M.H. , Van Deusen D.
Published: February 2023

Vertical cavity surface-emitting lasers (VCSELs) have generated a great deal of interest due to the potential cost and performance advantages of the vertical structures. VCSELs operating at 850 nm have already entered the commercial market, while long wavelength (1300/1550 nm) VCSELs have lagged in their development. A few groups have demonstrated room-temperature continuous wave (CW) operation [1,2,3], with the highest output power (0.5 mW @ 25°C) and operating temperature (64°C) achieved at 1550 nm [1]. In this work, we describe 1300 nm VCSELs with an integrated 850 nm VCSEL optical pump [4].
A novel design of diffractive optical interconnects for multichip clock distribution
Authors: Mennerat Sophie , Paineau Sylvain
Published: February 2023

We report a novel system of diffractive optical interconnects for very high speed clock distribution among multichip modules. Our system distributes two clock signals, each from one separate Vertical Cavity Surface Emitting Laser (VCSEL) over four PIN diodes positioned within a radius of 9 mm along a light-guiding glass plate. The incoming optical gaussian beams from VCSEL are splitted by diffractive optical elements into four output beams and the glass plate propagates the light through multiple reflections onto the golden metallized faces towards the detectors. The overall alignment and chromatic acceptance is highly improved by the use of SELFOC micro-lenses that collimate the laser beam onto the diffractive optical element and that focus the output beam onto the active area of the detectors. The proposed architecture allows tolerance on the light source wavelength as high as Δλ = 10 nm and global tolerances of assembly of the glass plate of 1.5 degrees in rotation and 10 µm in translation making it compatible with the processes of hybridization in microelectronics.
Single-pass distortion correction using innovative holographic methods in rhodium-doped barium titanate
Authors: Corner L. , Damzen M.J.
Published: February 2023

An important problem in the area of optical image processing is that of removing distortions introduced onto the image. Methods of distortion correction include phase conjugation [1] and holography [2], but these methods generally involve a double pass through the distorter. This either returns the image to its starting position, or requires a pass through a second distortion as close as possible to the original.
Efficient Second-Harmonic Generation in a Directly-Bonded, Buried, PPLN Planar Waveguide
Authors: Gawith C.B.E. , Shepherd D.P. , Abernethy J.A. , Hanna D.C. , Ross G.W. , Smith P.G.R.
Published: February 2023

Periodic poling of LiNbO3 to achieve quasi-phase matching for non-linear frequency conversion has generated a great deal of interest due to the fact that it allows the use of a large non-linear coefficient and eliminates walk-off effects. Combining such material with a waveguide geometry to increase average pump intensities is a promising route to the realisation of various compact non-linear devices based on harmonic1 or parametric2 generation. Here we present the first fabrication of a PPLN planar waveguide by direct bonding. This technique, which has previously been used to fabricate laser waveguides3, is based on the precision polishing of bulk material to waveguide dimensions. Hence the full non-linearity of the bulk PPLN should be maintained while offering versatility in the fabrication of exotic waveguide structures.
Industrial Applications of Pulsed Laser Micromachining
Authors: Gower Malcolm C
Published: February 2023

During the past decade, excimer lasers have led the way in applying ablative material removal to micromachining applications in manufacturing industry. Recently short-pulse versions of more familiar industrial CO2 and Nd:YAG lasers have also begun to be used for this application.
Micromachining of Miniaturized Components of Shape Memory Alloys by Ultrashort Pulse Lasers
Authors: Haferkamp H. , von Alvensleben F. , Goede M. , Paschko S.
Published: February 2023

The application of small components of shape memory alloys (SMA) finds increasingly attention in miniaturized medical engineering as well as in micro system engineering. However, only a few processes are available for machining of miniaturized SMA-components. The main problem is not to modify the special shape memory properties by thermal influence or mechanical tensions. During the machining process, changes of the shape memory properties due to the extension of the heat effected zone or mechanical tensions have to be avoided. Especially for complex geometries with dimensions in the submillimeter-range these requirements are hardly to fullfill. At present, the lack of suitable manufacturing processes for the realisation of form-fitting combinations with different kinds of materials strongly limits the applications of miniaturized SMA-components. Micromachining of those components employed at this time (electroerosive micro-processing, electrochemical etching, micro-mechanical processing) are strongly limited with regard to their achievable rate of removal and their flexibility. Further disadvantageous characteristics of these processes are the high complexity and the limited handling capabilities.
Direct Write Micromachining Using High Repetition Rate UV Lasers
Authors: Illy Elizabeth K. , Withford Michael J. , Brown Daniel J.W. , Piper James A.
Published: February 2023

Laser micromachining is rapidly emerging as a unique manufacturing process for the miniaturisation of mechanical and electronic components. The laser most suited to these applications is a UV source, because the high material absorption at short wavelengths results in ‘clean’ ablation of the target material, as well as giving the optical resolution necessary to achieve micron accuracy. Although the excimer laser is the most widely used UV source, frequency doubled copper vapor lasers represent an attractive alternative for numerous applications. The frequency doubled copper vapor laser (255, 271, 289nm) operates at similar wavelengths to excimer lasers, and has the advantage of running at elevated pulse repetition frequencies of up to 20kHz, compared to 1kHz for excimer lasers. This feature makes them useful tools for investigating and developing a fuller understanding of the processes governing the manner by which the ablation rate for different materials scale with source repetition rates.
All-Optical Switching in Distributed-Feedback Multiple-Quantum Well Waveguides
Authors: Coriasso C. , Campi D. , Cacciatore C. , Mautino S. , Faustini L. , Muzzani P. , Stano A. , Rigo C.
Published: February 2023

In this paper we report our work on the development of a distributed-feedback (DFB), multiple quantum-well (MQW) waveguide which has demonstrated the potential of this structure for all-optical device applications in the field of telecommunication. This work has led to the achievement of all-optical switching, between forward and backward propagation directions, with control energy of 1 pJ, recovery time of 0.6 ns and on-off ratio of 17dB, at a wavelength of 1.55 μm.1 The device is based on the nonlinear displacement of its grating stop-band and is suited for monolithic integration with other photonic devices, such as semiconductor optical amplifiers.
Planar monolithic integration of a photoconductive switch and a nipi-modulator into a smart pixel for opto-optical switching
Authors: Fix W. , Oehler C. , Knüpfer B. , Geißelbrecht W. , Döhler G.H. , Veiling P. , Prost W. , Tegude F.-J.
Published: February 2023

In this paper we report the first successful regrowth and processing of a normal- incidence nipi- modulator monolithically integrated with a special photoconductive switch into a smart pixel. Previously we have demonstrated that our special photoconductive switch provides high output currents suitable to drive directly either an electrooptical modulator or a surface emitting vertical cavity laser in hybrid versions of novel smart pixels with excellent performance data [1]. Surface-normal electro-optical modulators based on n-i-p-i- structures are very attractive components for smart pixels because they allow high-speed operation, require low driving voltage, exhibit high switching contrast and have a wide spectral bandwidth [2]. The MBE growth of the n-i-p-i- modulators requires the Epitaxial Shadow Mask technique (ESM-MBE). In order to integrate monolithically n-i-p-i modulators grown by ESM-MBE with our photoconductive switches into smart pixels we have developed a new InGaP/GaAs mask technology in which the p-i-n structure for the fabrication of the switch is part of the shadow mask layer structure, as depicted in Fig. 1. The key feature for this technology is the extremely high bi-directional etch selectivity of InGaP/GaAs.
Processing Information with Arrays of Spatial Solitons
Authors: Firth W. J. , Partners Pianos
Published: February 2023

Spatial solitons in cavities are being investigated with a view to applications in parallel information processing [1]. Such arrays offer functionalities which are beyond any micro-structured material array, whether optical or electronic. This paper discusses the basic physics of the nature, experimental demonstration and control of spatial solitons in cavities [1], and discusses processing schemes which take advantage of their unique properties. Such schemes avert the unequal competition with silicon which has plagued other all-optical processing schemes.
Development of Metal Oxide Multilayer Reflectors for Water-Window Wavelengths by Atomic Layer Deposition
Authors: Matsuyama H. , Kumagai H. , Iimura Y. , Midorikawa K. , Obara M.
Published: February 2023

High performance normal incidence multilayer optics has been required for water-window wavelengths raging from 2.33 to 4.37 nm, at which soft x-ray microscope can be expected for living cells. Various fabrication studies have been reported with multilayer structures of W/Sc, W/B4C, and so on. However, high reflectance enough to be practically used has not been obtained, because surface roughness, imperfections of interfaces and atomic-scale controllability of layer thickness are technical issues to be solved in these wavelengths. We have developed novel metal oxide multilayers with amorphous titanium oxide and aluminum oxide fabricated by atomic layer deposition technique, which can preferably prevent from making an alloy at the interface. This technique makes it possible to control the film thickness on an atomic scale due to self-limiting adsorption mechanism in surface chemical reactions.
Light Emission in Periodically Microstructured Porous Silicon
Authors: Squire E.K. , Snow P.A. , Russell P. St. J. , Canham L.T. , Simons A.J. , Reeves C.L.
Published: February 2023

It has been shown experimentally that the periodic microstructuring of the porosity in porous silicon (PS) resonant cavity light emitting devices (RCLEDs) radically improves their emission linewidth and beam quality1. However, an important issue not yet fully addressed is the precise role played by this periodic microstructuring, given that the luminescence is distributed throughout the whole structure and that the low porosity layers are highly absorbing. A greater understanding of this emission process is clearly essential for the optimisation of PS LEDs.
Ultimate Precision in Micromachining due to Extreme Energy Containment by Laser Pulses down to 5 fs
Authors: Kautek W. , Krüger J , Lenzner M. , Sartania S. , Spielmann C. , Krausz F.
Published: February 2023

Laser-micromachining of steel and glass with laser pulses below 100 fs, and even as short as 5 fs, exhibit unreached ultimate processing precision. Recent experimental studies of dielectrics in the pulse duration domain τ ≥ 140 fs [1,2,3] and even down to 20 fs [4,5] and 5 fs [6] showed that impact (avalanche) and multiphoton ionization contribute to the ablation process. Heat affected zones reached in the pulse duration domaine between 5 and 100 fs are of the same order as have been observed with longer sub-picosecond pulses (e.g. 300 fs). However, multiphoton absorption at lowest pulse durations and maximum intensities, respectively, yield a maximum energy containment in the irradiated material. It is shown that this reduces the ablation depths below values achieved by conventional sub-picosecond pulse laser systems. This and a substantial decrease of the ablation threshold fluence in respect of pulse laser processing with pulses in the picosecond and nanosecond range opens a new field of ultraprecision dry etching in micro- and nanotechnology.
Pulse length dependent laser ablation of polymers
Authors: Beinhorn F. , Ihlemann J.
Published: February 2023

Laser ablation of polyimide (PI) and polymethylmethacrylate (PMMA) at 248 nm with pulse lengths varied over six decades, from 200 fs to 250 ns, is presented. In order to obtain the desired pulse lengths in the femto- and picosecond range, the chirped 500 fs pulses of a hybrid dye-excimer laser system were modulated by a stretcher/compressor setup, mainly consisting of a pair of parallely mounted holographic reflection gratings with adjustable spacing, that introduces a defined group delay dispersion. Ablation was performed in vacuum with a mask projection setup.
Time of flight measurement during femtosecond laser ablation of Gallium Arsenide
Authors: Cavalleri A. , Sokolowski-Tinten K. , Bialkowski J. , von der Linde D.
Published: February 2023

Time of flight (TOF) distributions of evaporated particles from the surface of GaAs have been measured in order to determine its maximum temperature during femtosecond irradiation (100 fs, 620 nm). A quadrupole mass spectrometer (QMS) provides the TOF distribution of a given particle mass after laser excitation.