bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser diagnostics of natural organic complexes in water environment
Authors: Fadeev Victor V. , Chubarov Vasilii V. , Filippova Elena M.
Published: February 2023

The ecological state of water environment is characterized by the contents of some organic substances in water. Due to the fluorescence properties of many organic compounds the laser fluorescence spectroscopy is widely used for remote sensing monitoring of natural water. In this paper the possibilities of laser spectroscopy were investigated to diagnose simultaneously the three most important ingredients of natural water: dissolved organic matter (humic substances), dissolved proteins, and petroleum hydrocarbons in dissolved-dispersed state. In our opinion the basic problem of fluorescence diagnostics is superposition of fluorescence bands from different organic substances. Getting information from sea water spectra is a very difficult task. For the solution of this problem the optimal wavelength range for fluorescence excitation of humic substances, petroleum hydrocarbons, and proteins was determined in this paper.
Ho:YAG laser applications in eye posterior segment surgery for cutting and coagulation
Authors: Boiko E. V. , Danilichev V. F. , Smirnov N. N. , Lazo V. V.
Published: February 2023

Usage of pulsed mid-infrared laser energy, which has short absorption length in water, offers the possibility of photoincision and photocoagulation in vitreore- tinal surgery. Cutting effects and coagulative properties of experimentally and clinically used CO2 laser (J. B. Miller et al., 1978, 1980, 1981) and Er:YAG laser (Margolis T. I. et al., 1989) were highly evaluated by authors. Widespread acceptance of these lasers now is limited because of insufficiently convenient fiberoptic delivery systems.
Laser fluorescent flow citometer with pulsing excitation
Authors: Zinoviev A. V. , Gorelik I. G. , Khusainov I. A. , Usmanov T.
Published: February 2023

The flow citometry is one of the most perspective methods for investigation of the biological cells, in particular, their optical characteristics such as light scattering and fluorescence.1 For the excitation of fluorescence the nonpulsed lasers of various types are most-used that, naturally, limits the maximal value of excited irradiance and, moreover, does not permit the time-resolved investigation of fluorescence.
Investigation of Er-laser dynamics
Authors: Altshuler G. B. , Belikov A. V. , Gagarski S. V. , Erofeev A. V.
Published: February 2023

Recently, the effective generation in 3mm range has been obtained in several laser hosts (YAG, YSGG, YAP, YLF, GGG, etc.). The advantages of 3-mm lasers application in medicine stimulate not only the search for new laser media but the investigations of their operation as well. The pecularities of temporal behaviour of laser pulses are not discussed in literature devoted to application of this radiation in medicine. However, in some cases it is the temporal structure that determines the mechanisms of interaction of laser radiation with tissues. Therefore, the investigation of dynamics of 3-mm laser generation is of great importance.
Local distribution of the fluorescence in Nd-doped preforms
Authors: Reichel V. , Müller H.-R. , Schwuchow A.
Published: February 2023

The development of rare-earth-doped single-mode optical fibers based on silica for the use in diode-pumped fiber lasers with a high cw-output power demands the investigation of the local distribution of the rare-earth component in the fiber core. Hence, we developed a novel, nondestructive measurement method for the determination of the local distribution of the fluorescence of the rare earth-doped preform. Such measurements allow to draw conclusions to the concentration distribution of the rare-earth component in the preform.
Push-pull polyenes with enhanced quadratic nonlinear susceptibilities
Authors: Runser Claude , Barzoukas Marguerite , Fort Alain , Blanchard-Desce Mireille , Lehn Jean-Marie
Published: February 2023

Organic molecules have been extensively studied in view of their potential applications for second-harmonic generation and electrooptic modulation in nonlinear optics.1 Molecules bearing a donor- acceptor (or push-pull) substituted π electron system can yield significant quadratic hyperpolarizabilities β. In addition, early experimental studies on para disubstituted polyenic systems have shown superlinear dependences of β with the length of the conjugation path linking the electron-donating and electron-accepting end groups.2−4 Also semiempirical calculations conducted on two series of push-pull polyene series predicted a rapid increase in β with the number n of double bonds, the effect per unit volume saturating beyond n = 20.5 Clearly longer push-pull polyenes are relevant candidates for the design of compounds with dramatically enhanced nonlinearities.
Synthesis and study of glasses doped with semiconductor quantum dots
Authors: Lipovskii A. A. , Litvin I. D. , Sitnikova A. A. , Soloviev S. A.
Published: February 2023

Glasses doped with microcrystals are interesting both for fundamental study of quantum size phenomena and for applied optics. The last is due to nonlinearity of the glasses,1 lasing,2 and sharp transmission edge. Quantum dots-II-VI microcrystals-arise and grow within a semiconductor-doped glass under annealing. Results on synthesis and characterization of a novel Cd-S-doped phosphate glass (P-glass), a silicate glass (Si-glass) with increased concentration of Cd-S-Se microcrystals, and data on formation and study of ion-exchanged optical waveguides in the Si-glass are presented.
New nonlinear optical materials in the mixed (2,4-dinitrophenyl)-L-alanine (DPA) and 2-methyl-4-nitroaniline (MNA) system: crystal growth and investigation
Authors: Rao S. M. , He K. X. , Lal R. B. , Evans R. A. , Loo B. H. , Chang J. M. , Metzger R. M. , Lee W. J. , Shields A. S. , Penn B. G. , Frazier D. O.
Published: February 2023

Among innumerable organic materials investigated for their exceptional nonlinear optical (NLO) properties 2-methyl-4-nitroaniline (MNA) has one of the largest second-order nonlinear coefficients, χ(2)(d12 = 38 and d11 = 250 pm/V),1 crystallizing in the monoclinic space group Cc.1 Large crystals of MNA could not be grown from either solution or melt. Therefore, we tried crystallizing mixtures of methyl-(2,4-dinitriphenyl)-aminopro-panoate (MAP) and MNA2 from organic solutions. Large prismatic orange-red colored crystals of an equimolar complex crystallized in the monoclinic space group P21 with lattice parameters different from those of either MAP or MNA.3 The color, ascribed to a band starting at 530-nm, reduced second-harmonic generation (SHG) efficiency.3 Therefore, MAP was substituted by the precursor in its synthesis, (2,4-dinitrophenyl)-L-alanine (DPA).4
Double phase conjugate mirror: oscillation and amplification properties
Authors: Petrov M. P. , Korneev N. A. , Sochava S. L.
Published: February 2023

A double phase conjugate mirror (DPCM) is a device that performs a phase conjugation simultaneously for two mutually incoherent pump beams via four-wave mixing in photorefractive media (Fig. 1).1 Recent resurgence of interest to this scheme was caused by the theoretical controversy concerning the nonoscillating character of its operation.2,3 The exact solution suggested by Zozulya is rather complicated, which makes difficult its application to a real experimental situation. We propose a simple approximate solution for the case of small angles between pump beams (α << 1/d, where l is the aperture of the interacting beams and d is the crystal thickness) which is typical of the nonstationary holographic recording in BSO-type crystals.4
Self-pumped phase conjugation in a solid-state gain medium
Authors: Green R. P. M. , Crofts G. J. , Syed K. , Damzen M. J.
Published: February 2023

Self-pumped phase conjugation using a nonlinear material in a self-intersecting loop geometry is particularly attractive for its simplicity and efficiency. Loop systems based on photorefractive media1 and Brillouin-active media2 have been most extensively investigated. A few investigations have also been made of gainmedia in loop geometries,3-5 although several issues relating to conjugation fidelity and the implementation of this device as a practical laser source have not been fully addressed. We present the results of investigation of the spatial, temporal, and energy characteristics of the solid-state gain medium Nd:YAG in a loop configuration. The gain loop conjugator can also be considered as an adaptive laser resonator with oscillation from a volume gain-grating (gain hologram).
Self-pumped phase conjugation in low-absorbing nematic liquid crystal with a nonreciprocal loop scheme
Authors: Antipov O. L. , Kuzhelev A. S.
Published: February 2023

Self-pumped phase conjugation (SPPC) by near-forward stimulated thermal scattering was observed in nematic liquid crystals (NLC) with absorbers.1,2 The threshold of parametric generation (caused by thermal nonlinearity) for pumping waves of equal intensity is much higher in low-absorption NCL, which makes SPPC more difficult to achieve. However, it is this kind of media that can be used for SPPC of high-average-power laser beams. In this work we studied possibilities of reducing the parametric generation threshold in low-absorbing NLC with a nonreciprocal loop scheme.
Joint transform optical correlator using cesium vapors
Authors: Le Duc Emmanuel , Jonathan Jean-Michel C. , Roosen Gérald
Published: February 2023

Joint Transform Correlators (JTCs)1,2 have been developed using various recording materials. Their main drawbacks are speed, necessary thickness, and expensive laser sources. Resonant nonlinearities3,4 are possible answers to those difficulties.
An interferometric tracking and recognition of remote objects
Authors: Ivakin E. V. , Kitzak A. I. , Ben V. N.
Published: February 2023

An interferometrically modulated illumination of remote objects is of interest for robotized viewing and guiding systems design.1,2 Our report deals with both theoretical and experimental study of heterodyne modulation techniques for own movable units tracking and for rapid recognition of simple-shaped figures through a scattering or turbulent medium.
Peculiarities of four-wave mixing with feedback with an additional pc mirror in the CO2 laser radiation range
Authors: Betin A. A. , Ergakov K. V. , Mitropolsky O. V. , Ossipov D. V.
Published: February 2023

The scheme of phase conjugation (PC) in four-wave mixing with feedback (FWMF) using an amplifier in the feedback loop is a laser controlled by an external optical signal. Note that in this scheme the generation is, generally, developed simultaneously in two directions and is withdrawn through a nonlinear medium as the useful reflected wave E
r
counter to the signal and the parasitic wave E
p
copropagating with the signal. The energy of the parasitic wave E
p
often proves to be higher than the energy of the reflected wave E
r
.1,2 Thus, the problem of providing the unidirectional propagation of the conjugate wave is urgent.
High-efficiency conversion of powerful femtosecond pulses into second harmonic
Authors: Gordienko V. M. , Magnitskii S. A.
Published: February 2023

In recent years interest in second-harmonic generation (SHG) has been increased. First of all it is connected with the use of second-harmonic converters in powerful femtosecond laser systems for expanding their spectral range.
Quasi-periodic route to chaos in erbium-doped fibre laser
Authors: Sanchez F. , Le Flohic M. , Stephan G. M. , Francois Pierre-Luc
Published: February 2023

Rare-earth doped fibre lasers had demonstrated a large variety of dynamical behaviors including static and dynamic polarization effects,1 antiphase and chaotic dynamics in autonomous2 or modulated systems.3 In this context, erbium-doped fibre laser (EDFL) takes a privileged place due to its spontaneous different dynamical behaviors.4,5 Indeed, EDFL operates spontaneously in self-pulsing, sinusoidal, or CW regimes. These dynamical behaviors have been experimentally4 and theoretically5 attributed to the existence of ion clusters (ion pairs are sufficient) which act as a saturable absorber. In this communication we report the experimental evidence of a quasi-periodic route to chaos in self-pulsing EDFL operating simultaneously at 1.550 μm and 1.536 μm.
Efficient frequency tripling of ArF laser in a hydrogen gas jet
Authors: Maeda M. , Hirakawa Y. , Okada T. , Muraoka K.
Published: February 2023

Higher harmonic generation in the extreme-ultraviolet (XUV) region is also demonstrated in rare gas jets, but the conversion efficiency is poor. High-brightness coherent source with high repetition rate has not ever been developed in XUV region. We found that the efficient third-harmonic generation (THG) of an ArF laser was obtained by the resonant enhancement of χ3 when the laser was tuned at one of the two-photon resonant lines of hydrogen molecules.1-3 Using this scheme, we can build up a 64.4-nm XUV coherent source with high average power. This light source will be useful for practical applications such as optical processing, because the coversion scheme is very simple.
Pulsed photoacoustic detection of CO2 and C2H4 in infrared region
Authors: Terzic M , Cvijin P. Vujkovic , Markusev D. D. , Jovanovic-Kurepa J.
Published: February 2023

The detection of air pollutants in the atmosphere is of interest both from the physical point of view and from the atmospheric environmental aspect. Air pollutants are monitored by gas chromatograph techniques or, with better detection limits, by photoacoustic spectroscopy (PAS). The sensitivity of infrared (IR) photoacoustic (PA) detectors is limited not only by the magnitude of the background signal, but also depends on the gas constituents. The presence of CO2 gas in gas samples leads to the decrease of the amplitude of the detected PA signal, due to the effect of the kinetic cooling. Only few IR gas-phase PAS investigations have been made with pulsed CO2 laser sources.1,2
High efficiency Raman amplification of waves with conformed profiles
Authors: Begishev I. A. , Kulagin I. A. , Usmanov T.
Published: February 2023

In the case of the scattering Raman amplification of light beams in a field of powerful ultrashort pulses, the back influence of the amplified radiation on the fundamental wave may be significant. Moreover, properties of the media, such as a population of atomic states, may significantly change. That leads to amplitude-phase modulation of the fundamental pulse owing to change of direction of intensity exchange in the pulse.1 As a result, the bond between the fundamental and Stokes waves becomes weaker, that results in a decrease in the frequency conversion efficiency. For spatial inhomogeneous beams this effect is different in various beam sections.
Frequency dependencies of third optical harmonic generation efficiency in gaseous media under self-action conditions
Authors: Kulagin I. A. , Usmanov T.
Published: February 2023

The frequency conversion efficiency is well known to be determined by the intensity and focusing level of the fundamental radiation as well as microscopic medium parameters.1 Among the latest ones are linear susceptibilities responsible for phase mismatch, nonlinear susceptibilities responsible for generation process, and also Kerr nonlinearities responsible for nonlinear change of phase conditions of the process. The influence of Kerr nonlinearities can restrict the frequency conversion efficiency and can open up possibilities for short length generation according to the relation between linear and nonlinear phase mismatch effects.2
Optical investigation of electric breakdown in dielectric liquids
Authors: Barmann P. , Kröll S. , Sunesson A.
Published: February 2023

A novel technique to initiate1 and diagnose electric breakdown in dielectric liquids is presented. The electric breakdown is triggered between two high-voltage electrodes by a laser-induced plasma. In the initial phase of the breakdown process, thin light-emitting conducting channels (so-called streamers) are formed in the liquid. The streamers have a key role in the electric breakdown and a technique for optical time-resolved and spectral analysis of streamers is described.
Parametric fluorescence in periodically poled lithium niobate waveguides
Authors: Baldi P. , Aschieri P. , Nouh S. , de Micheli M. , Ostrowsky D. B. , Delacourt D. , Banti X. , Papuchon M. , Tartarini G. , Bassi P.
Published: February 2023

To date, parametric fluorescence and oscillation in lithium niobate waveguides have been demonstrated with crystal temperatures above 200°C, using pump wavelengths in the visible region (514 to 615 nm).1 In these experiments phasematching was achieved using crystal birefringence, imposing the use of the d31 nonlinear coefficient for the parametric interaction. More recently, we reported the use of first-order quasi-phase-matching (QPM),2 i.e., periodically inverted crystal domains, with a resultant periodic modulation of the sign of the nonlinear coefficient, which has permitted the generation of parametric fluorescence at ambiant temperature, using an 800 nm pump, and the d33 coefficient of lithium niobate3 which is approximately six times greater than the d31 coefficient. Emission has been observed in the 1.2 to 2.5 micron window of interest for optical fiber communication as well as optical sensors.
Frequency conversion in quasi-phasematching waveguides
Authors: Laurell F.
Published: February 2023

Quasi-phasematching (QPM) is a versatile technique for second-order nonlinear processes. A phase-velocity mismatch between the interacting waves are compensated for by a spatial modulation of the material's nonlinearity, which allows generation of arbitrary wavelengths within the transparency of the nonlinear material. This modulation is typically on the order of a few µms. With QPM it is also possible to use the strongest nonlinearity, d33, in crystals like LiNbO3, LiTaO3, and LTP.
New phenomena in pulsed far-infrared gas lasers
Authors: Kneubühl F. K. , Scherrer D. P. , Knittel J. , Moix D. B. , Baumgartner M.
Published: February 2023

Pulsed far-infrared (FIR) gas lasers have proven to be predestined for first realizations of new laser concepts, e.g., waveguide gas lasers, distributed (DFB), and helical (HFB) feedback gas lasers.
Transverse RF excited, table-top, fast-axial-flow CO laser with 1 -kW output power
Authors: Yu G. , Baker H. J. , Vitruk P. P. , Hall D. R.
Published: February 2023

RF excited, fast-flow CO lasers have a high conversion efficiency (~15-30%), being 1.5-2 times that of CO2 lasers at similar powers. The shorter CO wavelength provides a smaller focal spot size, a better absorption for many materials, especially for metals, and an availability of fibre delivery.1 Recently there has been extensive development of practical high-power fast-flow CO lasers2-4 aimed at showing this type of CO laser to be a potential alternative to existing CO2 lasers for industrial uses, particularly for material processing.
An optical force-feedback microphone measuring audible emissions from plants
Authors: Hadjiloucas S. , Karatzas L. S. , Keating D. A. , Usher M. J.
Published: February 2023

Detection of xylem cavitation audio acoustic emissions (AAE) and ultrasonic audio emissions (UAE) from plant tissues during periods of water stress are well known in the literature of plant physiology (Ritman and Milburn 1988, Ritman and Milburn 1991). Detection of the frequencies of emission generally depend upon attenuation by tissues and on the resonant properties of conduits (Fig. 1). It is generally accepted that tracheids are responsible for AAE but vessels are not essential for audio. Previous measurements reported in literature were limited by the dynamic range of the measuring microphone (Sandford and Grace, 1985).
Cavity build-up and transient fluctuations in optical-fibre-loop memories
Authors: Calzavara M.
Published: February 2023

The use of fibre-loop memories is being experimented for solving routing contention of data cells in photonic high bit rate ATM switching fabrics.1 The simplest fiber-loop memory looks like a ring laser consisting of a semiconductor laser amplifier (SOA), a span of fibre introducing a delay of the order of an ATM cell duration (10–6-sec) and a 50/50 directional coupler (Fig. 1). To compensate for the power tapping at the directional coupler while avoiding the onset of laser oscillations, the SOA is biased above the ring laser threshold only for a limited number of round trips, then the bias current is switched off. The memory is thus driven through the transition from a state ruled by spontaneous emission toward a state above lasing threshold, in which stimulated emission is predominant. Far enough from the beginning of the transition the intensity fluctuations display a maximum.2,3 The transition is completed after a time depending on the final state intensity.2 These features significantly affect the maximum storage time and noise behavior of the memory.
Fault-locating technique for multi-staged optical distribution networks
Authors: Chen Yung-Kuang , Chi Sien
Published: February 2023

Optical power splitters are extensively used in many fiber-optic distribution networks such as CATV and fiber-to-the-home systems. Techniques for locating any fiber link faults become more important after the installation of such distribution networks. However, today's optical time-domain reflectometer (OTDR) is unable to diagnose N-branched networks, e.g., N > 4, due to lack of high spatial resolution with sufficient singleway dynamic range (SDR). To overcome this problem, we propose and demonstrate a fault-locating technique for large multistaged branched networks. The requirement of ultra-wide SDR with high resolution of an OTDR to diagnose a large distribution network can be tremendously relaxed by the introduction of optical switches and the wavelength division multiplexing technique.
82% efficient monolithic frequency doubler
Authors: Paschotta R. , Kürz P. , Fiedler K. , Henking R. , Schiller S. , Mlynek J.
Published: February 2023

In the last few years there has been increasing interest in frequency doublers used as powerful light sources at wavelengths that are not directly accessible by suitable lasers. One important goal is to reach high conversion efficiencies; about 50% or more was achieved in several experiments,1-4 most of them using LiNbO3(often doped with MgO) because of its high nonlinear coefficient and the uncritical type-I phase-matching for 1064/532 nm.
Periodically poled lithium niobate for bulk optical frequency doubling
Authors: Webjörn J. , Pruneri V. , Russell P. St. J. , Barr J. R. M. , Hanna D. C.
Published: February 2023

Quasi-phase-matching (QPM) has attracted much interest for second-harmonic generation (SHG).1,2 In this paper we present SHG experiments in periodically poled lithium niobate, fabricated through field poling via liquid electrodes. The experimental phase-matching bandwidth of a 3.3-mm bulk crystal was equal to the theoretically expected value, indicating that the domain inversion was uniform throughout the volume of the crystal.
Cerenkov second-harmonic radiation from organic calix[4]arenes thin films
Authors: Noordman O. F. J. , van Hulst N. F. , Bolger B.
Published: February 2023

Nitro-calix[4]arenes are a novel type of organic molecules. In a thin film the material shows high nonlinear optical properties combined with good temporal stability at room temperature.1,2 Furthermore, a nitro-calix[4]arenes film is transparent down to 400 nm, which makes it suitable for frequency doubling of laser-diodes.
Femtosecond pulse lasers for nonthermal tissue ablation
Authors: Loesel F. H. , Brockhaus P. , Fischer J. P. , Götz M. H. , Tewes M. , Niemz M. , Bille J. F. , Noack F.
Published: February 2023

Ultrashort laser pulses enable a process of tissue ablation that is of great interest for medical therapy. In contrast to long pulsed or cw lasers, where the applied energy leads to heating and vaporization of irradiated tissue, the ablation process in the ultrashort pulse range is initiated by a plasma formation in the laser focus, resulting in tissue removal.1 Using picosecond pulses this ablation mechanism is already well established in ophthalmology. The accuracy and the absence of undesired thermal side effects made the plasma-mediated ablation a promising technique in other medical fields, e.g., neurosurgery.
Ablation effects on teeth depending on laser wavelength and pulse duration
Authors: Niemz M. H.
Published: February 2023

The aim of this study was a qualitative comparison of ablation effects induced by different laser parameters. Three self-built laser systems were applied to the enamel of extracted human teeth: a microsecond Ho:YAG laser at a wavelength of 2.12 μm, a microsecond Er:YAG laser at 2.94 μm, and a picosecond Nd:YLF laser system at 1.053 μm. After laser irradiation, the teeth were critical point dried, coated with a gold layer of about 30 nm, and examined by a scanning electron microscope (Amray 1810).
Monolithically integrated cavity mode-locked two-segment semiconductor lasers at 1.5 μm
Authors: Baums Dieter , Lach Eugen , Schilling Michael , Daub Karin , Idler Wilfried , Zielinski Erich , Wünstel Klaus
Published: February 2023

We report on mode-locking of monolithic cavity fully active two-segment lasers at 1.5 μm and frequencies around 20 GHz. The lasers need very low cw threshold current and modulation power. Optical pulses shorter than 16 ps are observed.
Progress in high-power femtosecond excimer lasers
Authors: Szatmäri S.
Published: February 2023

In view of the recent advances in femtosecond solid-state technology, highpower solid-state laser systems are regarded as superior light sources over excimer-based short-wavelength systems. Based on the well-developed high-energy amplifier technology and using the so-called Chirped-Pulse-Amplification (CPA) technique, peak powers of several tens of TW have been reached.
Generation of tunable XUV radiation by high-order frequency mixing
Authors: Eichmann H. , Meyer S. , Riepl K. , Momma C. , Wellegehausen B.
Published: February 2023

Currently, there exists considerable interest in the generation of coherent radiation in the xuv spectral range. Due to the development of compact short-pulse highpeak power laser systems, high-order harmonic generation has become a useful laboratory tool. Harmonics up to very high orders and wavelengths below 10 nm have been demonstrated.1 For applications, tunable coherent XUV radiation is of great importance. One way to achieve this is to tune the main pump laser directly. However, the disadvantage of this approach is, that the high power lasers systems are only slightly tunable (excimer, Nd:glass) or if broadly tunable (Ti:sapphire) are optimized for a specific wavelength. A more flexible approach is to mix very powerfull pump laser radiation (ωP) with a less powerfull but tunable light source (ωOPG), generating tunable photons at n · ωP ± k· ωOPG. To achieve high orders in ωP (high n) intensities of more than 100 GW have been used, while for ωOPG intensities of about 100 MW are sufficient to detect at least mixing signals with k = 1. Similar experiments using the non-tunable second harmonic of a Nd: glass pump laser have been reported in [2].
Photonic bandgaps and semiconductor electronics
Authors: Yablonovitch E.
Published: February 2023

Summary not available.
From micromasers to microlasers
Authors: Walther H.
Published: February 2023

The one-atom maser or micromaser is, in contrary to ordinary masers and lasers, a pure quantum device operating with only a few photons and less than one pump atom on the average in the maser cavity. It is thus an ideal device to study quantum phenomena such as the generation of nonclassical light. The cavity is a superconducting niobium microwave resonator with a high quality factor (up to 3 × 1010). Using a single trapped ion related experiments can now also be performed in the infrared spectral region.
Suppression of quantum noise in optical physics
Authors: Knight P. L.
Published: February 2023

The search for optical fields with quantum fluctuations less than that of a perfectly coherent signal has reopened questions of appropriate signatures of non-classicality. Squeezed light fields have phase dependent noise that for some phase angles can be substantially less than the normal vacuum fluctuations. Sub-Poissonian light has photon number fluctuations below those expected from naive "shot noise" considerations. In this talk, I will review the progress made in understanding non-classical light, and discuss measures of non-classicality.
Single Pulse Laser Ablation of Thin Metal Films
Authors: McNeill Debra , Dawson Paul , Tamm Ian , Morrow Tom
Published: February 2023

Tins study addresses die ablation of thin metal (principally Aluminium) films, induced by the incidence of a single pulse of ~ 20ns duration from a KrF eximer laser, operating at wavelength 248nm. Prior to the exposure the Aluminium film is characterised by means of surface plasmon (SP) excitation in an optical rig, also operating ~ 250nm, using an Xenon lamp and monochromator. This characterisation determines the dielectric functions and thicknesses of the Al and native Al-oxide, as well as precisely defining the angle for optimum SP excitation. The latter is crucial to surface plasmon enhanced laser ablation studies.
Scanning near-field optical lithography
Authors: Wegscheider S. , Georgi A. , Sandoghdar V. , Krausch G. , Mlynek J.
Published: February 2023

The resolution of various scanning probe microscopy methods can be applied to the fabrication of nanostructures. Various methods of local material modification based on different microscopic mechanisms have been proposed, examples of which are : material transfer between a scanning tunneling microscope (STM) tip and a substrate, local oxidation of silicon using atomic force microscope (AFM). Scanning near-field optical microscopy (SNOM) is also an attractive candidate for nanofabrication. Here the optical spot size in the near-field is given by the resolution of the SNOM which in turn is determined by the details of the tip geometry and is typically between 50 and 100 nanometers.
Enhanced Resolution of Stereolithography
Authors: Partanen Jouni P.
Published: February 2023

Stereolithography is a Rapid Prototyping & Manufacturing (RP&M) technique which can be used to produce 3 dimensional plastic parts directly out of computer files generated by CAD. RP&M systems build the 3-dimensional objects by first converting the data in the CAD files into a form of successive horizontal 2-dimensional slices. One slice at a time is then formed as a thin layer of the object and joined to the previously built layers. The raw material in a Stereolithography Apparatus (SLA) is liquid photopolymer resin. Layers are formed by solidifying the desired cross-section of a resin layer on the surface of a vat using an ultraviolet laser beam and two orthogonal scanning mirrors. This layer is simultaneously attached to previously build layers situating one layer thickness below the surface inside the photo-polymer resin vat.
Debris-free laser-plasma source for x-ray microscopy
Authors: Rymell L. , Berglund M. , Hertz H. M.
Published: February 2023

X-ray microscopy allows high-resolution imaging of biological samples in their natural aqueous environment without staining, sectioning or fixation. In particular attention has been focused to the “water window”, i.e., the wavelength region between the oxygen K-edge at λ = 2.3 nm and the carbon K-edge at λ = 4.4 nm, where different absorption coefficients for water and proteins create a natural contrast. Current, operational x-ray microscopes normally utilise zone-plate optics in combination with synchrotron sources. However, these sources suffer from drawbacks such as high cost, limited accessibility for biological researchers and relatively long exposure times. We have developed a compact high-brightness x-ray source based on a laser-produced plasma from a liquid droplet target [1]. A 10 Hz, 70 mJ, 120 ps laser is focused onto ~15 μm droplets generated from a capillary nozzle. By choosing different target liquids spectrally tailored emission can be obtained. For x-ray microscopy we use ammonium hydroxide droplets which generates nitrogen line-emission in the water window [2]. The spectrum over this region is shown in Fig. 1. The emission has been filtered through 600 nm of titanium in order to achieve quasimonochromacy. By using only N VI radiation at λ = 2.88 nm chromatic aberrations in zone plates are efficiently eliminated. Furthermore, λ/Δλ has been estimated to >440, which makes high-resolution imaging possible. Depending on the temporal laser parameters we obtain plasmas from a diameter of ~10 μm with unfiltered single-line flux of 3x1011 photons/(sr pulse) up to a diameter of ~35 μm with 3×1012 photons/(sr pulse) [3]. A major advantage using this new droplet target is the elimination of debris from the laser-plasma. Measurements have proven that the debris emission from the plasma based on ammonium hydroxide is more than 5 orders of magnitude less than from any other conventional low-debris target [4].
Scaling and screening in long MSM photodiodes
Authors: Wilson S.P. , Walker A.B. , Vickers A.J. , Hassan M.
Published: February 2023

MSM Photodetectors are strong candidates for use in high bit rate communicationsystems. Using conventional GaAs, bandwidths of up to 295 GHz have been measured [1]. It has been suggested that one way to improve the speed of these devices is to partially illuminate the photoconductive gap. The mechanism which gives rise to speed impovements is not fully understood [2]. The response has been found to be asymmetric with respect to the position of the focussed beam in the gap [3].
Optical coherence tomography of human skin with a slow-scan CCD-camera
Authors: Brunner H. , Lazar R. , Steiner R.
Published: February 2023

The most common tumour among adults is skin cancer. Regarding the USA. melanoma affects approximately 28.000 individuals per year, resulting in 5800 deaths. In the past 40 years there has been a 700 per cent increase of incidences [1]. Because of its distinct clinical features the tumour could be detected at a time, when cure by surgical excision is still possible. In order to perform a successful operation it is necessary to evaluate the thickness of the tumour, since it affects the diameter of tissue to be removed. To an extent of 0.76 mm in depth the tumour can be excised almost without any margin. Moreover the 5-year survival rate increases up to 95% with a recognition at such an early stage [2.3].
Selective Laser Inactivation of Periodontal Bacteria
Authors: Golding P.S. , Maddocks L. , King T.A. , Drucker D.B
Published: February 2023

Periodontal disease, caused by bacterial biofilms (plaques) on tooth surfaces, is one of the major causes of tooth loss in adults. The current method of treatment involves a labour-intensive, unpleasant scraping away of the plaque from within the periodontal pocket1. With the recognition that this disease is associated with specific organisms, increasing interest is being shown in the use of anti-microbial agents to kill the bacteria in situ.
Low-Threshold, All-Solid-State Femtosecond Cr3+:LiSAF and Cr3+:LiSGaF Lasers
Authors: Critten M.P , Burns D. , Sibbett W
Published: February 2023

Cr: LiSAF has attracted considerable attention in recent years as a gain medium for all solid-state femtosecond laser systems. Semiconductor-laser pumped Cr: LiSAF lasers provide a compact, efficient and reliable alternative to Ti: sapphire systems pumped by mainframe ion lasers However, the poor thermal properties of LiSAF have proved to be a significant drawback, and attention is now turning to another Cr3+ -doped colquiriite, Cr: LiSGaF1, which has a lower thermal expansion coefficient and a higher thermal conductivity than Cr:LiSAF, and also exhibits lower intrinsic losses.
Mode locking of solid-state lasers by use of a slow saturable quantum-well absorber
Authors: Herrmann J. , Müller M.
Published: February 2023

Recent experiments succeeded in sub-100fs pulse generation from solid-state lasers by use of a saturable single-quantum-well absorber (SQW) yielding self-starting 34fs pulses in a ti.sapphire laser [1] as well as 90fs pulses in a diode pumped Cr:LiSAF laser [2]. These experimental findings can hardly be explained by the common theoretical understanding of passive mode locking in solid-state lasers which requires a fast saturable loss for stable pulse generation. The relaxation of the absorption bleaching in a GaAs quantum well at room temperature exhibits a bitemporal behavior where the fast component of about 200fs owing to thermal ionization of the exzitons is remarkably slower than the meanwhile achieved pulse width in the experiments. Recently we have proposed a novel mechanism for mode locking a solid state laser by use of a slow off-resonant saturable two-level absorber [3]. Here we analyze the operating conditions for this new mode locking scheme by use of a slow saturable SQW-absorber and calculate the dependence of the pulse parameters on the characteristical laser and absorber parameters. The underlying principle of mode locking of this mechanism is that in a first order expansion beyond the rate equation approximation a slow saturable absorber with an arbitrary large response time T1produces an additional intensity dependent loss

Δ
α
=
−
γ

d
Δ
n

d
ω

I

, where Δnis the linear refractive index change owing to the near-resonant transition, γis an absorber parameter and I is the pulse intensity. The physical origin of the intensity dependent loss Δαis that due to the finite phase relaxation time τ
a
the coherent medium polarization encounters a group velocity change which leads owing to the slow saturation under off-resonance with

d
Δ
n

d
ω

|

ω
L

>
0

to a negative fast saturable loss term Δα< 0. To study this mechanism for a SQW absorber we consider a simple 2D free carrier band filling model [4]. Using these simplifications we derive the spectrum of the complex SQW-susceptibiliy χ(ω) in dependence on the optically induced carrier density N. Expanding the time-domain round trip operators with respect to small parameters we deduce a stationary mode locking equation which governs the steady-state pulse parameters of the mode locked laser. The calculated pulse parameters in dependence on the SQW and laser parameters shows that in a reasonably extended operating region a near-resonant slow saturable SQW-absorber always yields an additional fast saturable loss which is sufficient to provide and maintain stable passive mode locking in broad band solid state lasers. Thus, off-resonant slow passive mode locking (OPSM) [3] with a slow saturable SQW-absorber represents a reliable novel method for fs-pulse generation in solid-state lasers and can explain the main findings in recent experiments [1,2].
Compact high-repetition-rate sub-100-fs lasers
Authors: Stingl Andreas , Spielmann Christian , Krausz Ferenc , Szipöcs Robert
Published: February 2023

In conventional femtosecond solid state lasers, the intracavity prism pair imposes a severe constraint on the resonator length and thus on the maximum achievable pulse repetition rate. Aside from the problem of introducing negative dispersion in short cavities, the major difficulty in generating ultrashort pulses at high repetition rates relates to the fact that the duration of the solitonlike mode-locked pulse τ ≈ |D|/ϕW is inversely proportional to both the self-phase modulation coefficient ϕ and the intracavity pulse energy W (D is the net cavity group delay dispersion, GDD), both of which decrease as the cavity length is reduced. Hence, it is imperative that the magnitude of negative intracavity GDD is kept at very small values if femtosecond pulses are to be generated at high repetition rates. However, high-order dispersion severely limits the reduction of negative GDD in oscillators using refractive dispersive components. Chirped dielectric mirrors can be designed to be virtually free from high-order dispersion. Therefore their use as resonator mirrors overcomes not only the limitation imposed by prismatic dispersion compensators on the cavity length, but also allows reducing |D| to significantly lower values than attainable in prism-controlled systems.
All-Solid-State, Compact, Self-Mode-Locked Cr4+:YAG Laser
Authors: Valentine G.J. , Kennedy G.T. , Sibbett W.
Published: February 2023

Cr4+:YAG has a broad tuning range extending from 1.34 to 1.58 μm and is an attractive room temperature replacement for cumbersome, cryogenically cooled colour centre lasers in some applications. Recently, an all-solid-state self-mode-locked Cr4+:YAG laser was demonstrated1 producing pulses as short as 85 fs.
Femtosecond pulses generation by a pulsed all-solid-state synchronously pumped Ti:sapphire laser
Authors: Borisevich S .A. , Buganov O.V. , Tikhomirov S.A. , Tolstorozhev G.B.
Published: February 2023

Recently, pulses of sub-100 fs duration which are widely tunable in the near-infrared have become available on the basis of Ti:sapphire lasers by using different mode-locking techniques /1/. To date, practically in all experimental realizations gas or solid-state CW lasers were used as a pump source. Earlier attemptes to use nonstationary time-limited trains of conventional pulsed mode-locked solid-state lasers for synchronous pumping of Ti:sapphire laser were not successful. This is primarily because of the low gain modulation (less than 1%) owing to the long upper-state lifetime of the gain medium, as compare to that of the dye lasers. From the other hand the synchronous pumping of Ti:sapphire by cw mode-locked lasers is effective to produce picosecond seed pulses for Kerr lens mode-locking and generation of femtosecond pulses /2/.
Planar InP Waveguide Space Switches
Authors: Melchior Hans
Published: February 2023

Guided wave space switches are gaining importance in fiber optical communication networks. Planar space switches exploiting various electrooptic effects in LiNbO3, GaAs and InP they are making inroads into optical protection switching, routing and high-speed processing.
Diode-Pumped Nd:YVO4 Microchip Lasers Operating at 1342/671nm
Authors: Conroy R S , MacKinnon N , Matthews D G , Sinclair B D
Published: February 2023

Microchip lasers are typically formed by applying dielectric mirrors directly to two near-parallel surfaces of a thin slice of laser gain material. Nd:YVO4 is a commonly used gain material in microchip lasers because of its short absorption depth and high stimulated emission cross section [1,2]. The 4F3/2 – 4I13/2 transition of Nd3+ occurs at 1342nm in Nd:YVO4 with a stimulated emission cross-section of 5.88×10-19cm2 for 1% Nd3+ doping, 6 times larger than the 1.3μm transition in Nd: YAG [2],
A Thermally Bonded Nd:YAG Planar Waveguide Laser and Amplifier
Authors: Warburton T.J. , Shepherd D.P. , Tropper A.C. , Hanna D.C.
Published: February 2023

The planar waveguide geometry is an attractive one for lasers [1] and amplifiers [2] since it offers some confinement of the pump and signal fields together with good power handling characteristics. We have demonstrated laser oscillation and amplification in a Nd:YAG waveguide, fabricated from bulk material by a thermal bonding technique. The waveguide, manufactured by Onyx Optics, California, consisted of a 5mm long, 20μm thick, lat.% Nd YAG layer sandwiched between two undoped YAG slabs. A feature of this guide fabrication technique is that it does not decrease peak cross section values by introducing additional line broadening.
780 mW single-frequency radiation at 532 nm by second harmonic generation of a miniature Nd:YAG ring laser
Authors: Schneider K. , Schiller S. , Mlynek J. , Bode M. , Freitag I. , Tünnermann A. , Welling H.
Published: February 2023

Frequency doubling of solid state lasers is important for generating wavelengths which are not directly accessible by suitable lasers. Conversion efficiencies in externally resonant frequency doubling of single-frequency cw lasers of up to 85 % have been demonstrated [1,2,3].
Efficient Second Harmonic Generation at 1.5 μm in Composite Polymeric Channel Waveguides
Authors: Jäger Matthias , Stegeman George I. , Horsthuis Winfried H.G. , Möhlmann Guus R. , Flipse Marinus C.
Published: February 2023

Efficient Second Harmonic Generation (SHG) has been a continuing goal for not only frequency conversion but also for cascading effects such all-optical switching, spatial solitary waves, etc. To date high efficiencies have been demonstrated only in ferroelectric crystals However, some poled polymers have even higher nonlinear coefficients and offer ease of processing and low cost fabrication. Nevertheless, the efficiencies reported for poled polymers have never achieved expectations. We demonstrate phase-matched SHG in a channel waveguide made of 4-dimethylamino-4′-nitrostilbene (DANS) side-chain polymer. Our SHG figure of merit η=P2
ω
/(P
ω
L)2 = 10%/W-cm2 is the highest non-resonant value reported for polymers and is comparable to those of inorganic crystals.
Injection-Locked Nd:YAG High Power Lasers Pumped by Fiber-Coupled Diode Lasers
Authors: Freitag I. , Knoke S. , Tünnermann A. , Welling H.
Published: February 2023

For Michelson-type gravitational wave detectors a strain sensitivity of at least 10-21 is desired. This ultra-high sensitivity places challengingly high performance requirements on the laser light source. The laser has to work at high power levels in single-frequency operation (tens of Watts) with excellent frequency stability (FM-noise < 3·10-7Hz/√Hz
)
, and intensity noise as close as possible to the quantum noise limit. Beyond that, the lifetime of this system must be in the range of several 10.000h at low operational costs. We report on the development towards a diode-pumped Nd:YAG laser system, based on the injection locking technique, that fulfills these requirements.
Narrow Linewidth Millimetre-wave Generation by Optical Heterodyning of Two Vertical-Cavity Surface-Emitting Lasers
Authors: Dowd P , While IH , Tan MRT , Wang SY
Published: February 2023

The optical generation of millimetre-wave and microwave signals is a subject receiving much interest and may have applications in future radio distribution systems. Several optical generation techniques have already been investigated [1],[2],[3]. The generation of signals between 30 and 70GHz has been demonstrated using a DFB laser where the usual mode degeneracy was lifted and two modes were supported [1]. Modulation techniques have been used to produce narrow pulses with high harmonic content [2]. The generation of such beat signals has also been achieved over a range of frequencies up to -1THz using two single-moded edge emitting lasers [3]. Vertical-cavity surface-emitting lasers (VCSELs) arc attractive sources for such work due to their potentially lower cost compared with edge emitting devices. They are able to lase in a single longitudinal mode and their lasing wavelengths are readily tuneable by current and/or temperature. Since it is easy to integrate two devices on a single chip, a compact millimetre-wave source could be developed where current tuning of the beat frequency could be utilised. The generation of beat notes up to 20GHz wilh 3dB linewidths of 109MHz has already been achieved using a VCSEL array [4].
"Modal Spectroscopy" of multimode optical waveguides
Authors: Ulrich Reinhard , Stolle Ralf , Gnewuch Harald , Tartari Giovanni
Published: February 2023

In many integrated-optical devices operation is based on distributed coupling between two guided modes. Examples are directional couplers, travelling wave modulators and polarisation converters. In fabricating sudi devices it is a fundamental task to measure the propagation characteristics of these modes accurately enough for phase matching.