bluuebunny/crossref_metadata_2025 huggingface dataset:
Compact Visible Lasers in Reprographics
Authors: Owens James C.
Published: February 2023

Reprography, which originally referred only to printing and duplicating processes for the reproduction of flat originals, today includes a wide variety of technologies for the production of two-dimensional images in applications as diverse as photography, office copying, desktop publishing, graphic arts, medical imaging, and microelectronic fabrication. Although analog processes are still in wide use, the principal area of recent technical development and new application has been in digital electronic imaging systems, and especially in optical methods for non-impact hard copy printing.
Tm3+ Room Temperature Upconversion Laser
Authors: Thrash R. J. , Johnson L. F.
Published: February 2023

Diode laser pumped, room temperature upconversion lasers are one possible route to all solid-state visible wavelength lasers. The energy level spacing of the thulium ion is such that several visible laser transitions should be possible. Upconversion laser emission from Tm3+ at a number of visible wavelengths has been reported in bulk crystal1,2 and glass fiber3 hosts.
Inorganic Crystals for Frequency Conversion
Authors: Bordui Peter
Published: February 2023

Bulk organic crystals, including KTP, KNbO3, Mg:LiNbO3, and periodically poled LiNbO3, are known to offer attractive potential for frequency conversion devices. Although problems remain, significant progress has been made in developing these materials for practical application.
Organic Nonlinear Materials for Frequency Conversion: Property Trade-off and Recent Applications
Authors: Cheng L.-T.
Published: February 2023

Frequency doubling of short wavelength diode lasers has significant technological applications in imaging and optical recording. One of the major hurdles towards achieving efficient doubling remains to develop highly nonlinear materials with appropriate linear optical properties such as birefringence and transparency. One approach is to engineer materials by doping or grafting nonlinear organic molecules into transparent polymeric matrixes. Second-order nonlinearity is obtained by the acentric alignment of these molecules along their dipole moments under an external electric field. With this approach, several molecular properties are important, including large molecular dipole moment and hyperpolarizability inner product (μβμ) as well as very low absorption at the first and second harmonic wavelengths of diode lasers (near 800 and 400 nm). An established guideline in identifying organic molecules with large hyperpolarizabilities is by the presence of low-lying strong charge-transfer (CT) electronic transitions. However, such an approach is in conflict with the requirement of transparency.
Self-frequency-doubled high δn Proton Exchange Nd:LiNbO3 waveguide lasers
Authors: He Q. , De Micheli M.P. , Ostrowsky D.B. , Lallier E. , Pocholle J.P. , Papuchon M. , Armani F. , Delacourt D. , Grezes-Besset C. , Pelletier E.
Published: February 2023

Neodymium doped lithium niobate offers the possibility of combining laser action and non-linear effects in the same structure1,2. Low threshold, efficient, CW, proton-exchange (PE)3 waveguide lasers and amplifers at 1.085 microns have been fabricated4 and, recently, the integration of such a waveguide laser and an FM mode locker was demonstrated5. In view of the high nonlinear coefficients of lithium niobate, it would be interesting to combine parametric interactions, such as second harmonic generation (SHG), with the laser action. The "Cerenkov" doubling configuration appears to be the most interesting for this application since it provides automatic phase matching and the possibility of high efficiency, when realized with high 8n step index guides6. Here we report on what is, to our knowledge, the first high δn waveguide lasers in lithium niobate and the observation of SHG and sum-frequency mixing with these devices. Depending on the pumping level, the high δn devices typically lase simultaneously at several wavelengths, and while the conversion efficiencies of these first devices are rather low, essentially due to strains induced propagation losses which we shall describe, we outline the way to overcome this.
A Diode Pumped Self—Doubling Laser of Modified Neodymium Yttrium Aluminum Borate Crystal
Authors: Huo Yujing , Wang Pu , Cai Jinxing , Pan Hengfu , Zhang Qinqing , Xue Jing , Zhou Bingkun , Lu Baosheng
Published: February 2023

The blue—green lasers have great application in optical disk technology, image processing, color projection, printing and underwater optical communication. A good scheme for diode pumped frequecy doubling laser is diode pumpedself doublinglaser. In this kind of lasers, a single block of a compound—functionmaterial material was used both as the laser material to generate the fundmental laser and as the frequency doubling material to double the fundmental laser to the second harmonic, light. This kind of lasers have the advantages of compactness, high doubling efficiency, narrow breadth of spectrum line of second harmonic light, lower costs, and easy to adjust[1,2,3,4].
Quasiphase-Matching (QPM) in the Channel Rb:KTP Waveguides
Authors: Shcherbakov Eugene A. , Maslov Vladislav A.
Published: February 2023

In recent years, several techniques of formation the periodic domain-inverted grating (PDIG) in the different ferroelectric crystals were examined extensively. Mainly, the variety of the techniques was concerned with LiNbO3 and LiTaO3 crystals [1]. It was well established that formation of ferroelectric domains had strong dependence of the quality, conductivity and other physical properties of the crystals.
Generation of 425 nm light by waveguide frequency doubling of a GaAlAs laser diode in an extended-cavity configuration
Authors: Risk W.P. , Kozlovsky W. J. , Lenth W. , Lau S.D. , Bona G.L. , Jaeckel H. , Webb D.J.
Published: February 2023

There is currently considerable research on compact blue light sources that use periodically-poled waveguides for quasi-phasematched frequency doubling of GaAlAs laser diodes.1,2 For such devices to become practical, they must be configured in such a way that optical feedback from the SHG waveguide or the other optical elements does not adversely affect the spectral characteristics or increase the amplitude noise of the diode laser. Although optical isolators can be used to reduce feedback, this approach does not lend itself to miniaturization of such devices. A more attractive alternative is the use of a configuration that includes the frequency doubling waveguide and all other optical elements within an "extended" laser cavity. In this configuration, lasing due to the reflectivity of the diode laser output facet is suppressed by antireflection (AR) coating, and strong feedback is intentionally provided by an external mirror or grating to produce laser oscillation.
Digital Alloy Quantum Wells of CdSe/ZnSe: New Structures for Blue-Green Lasers
Authors: Luo H. , Short S. , Samarth N. , Yin A. , Pareek A. , Dobrowolska M. , Furdyna J.K. , Ahrenkiel P. , Al-Jassim M. , Peiris F.C. , Buschert J.R.
Published: February 2023

Rapid progress in ZnCdSe/ZnSe wide-gap semiconductor heterostructures has demonstrated the feasibility for applications such as blue-green semiconductor lasers. There are, however, still various problems that have to be resolved, among which is the quality of ZnCdSe alloy that comprises the quantum well region. A search of quantum wells with better optical characteristics lead to our study of digital quantum wells of CdSe/ZnSe. One of the advantages of CdSe/ZnSe digital alloys is the ordered crystal structure in the quantum well regions that might decrease alloy scattering of charge carriers. Most of the current interest in ZnCdSe/ZnSe prompted by applications is in the blue-green region, corresponding to Cd concentrations of less than 25%. We therefore focused our attention to structures consisting of various numbers of periods of 1 monolayer (ml) of CdSe and 3ml of ZnSe, which have an effective Cd concentration of 25%.
Second-order Optical Nonlinear Properties in Corona-poled Glass Films
Authors: Okada A. , Mito K. , Sasaki K.
Published: February 2023

Due to their optically isotropic properties inorganic glasses are not expected to exhibit second-order optical nonlinearity χ<2>. However, we have observed that χ<2> can be induced in radio-frequency(rf) sputtered Corning 7059 glass films by corona poling and realized phase-matched second-harmonic generation(SHG) in a corona-poled glass film waveguide.1 To elucidate the mechanism responsible for the induced χ<2> in the corona-poled glass films is not only interesting from a physical point of view but also serves to develop new glass films with a large χ<2>.
Overview of Bulk SHG Activities in Japan
Authors: Sasaki Takatomo
Published: February 2023

The developement of compact blue-green laser sources by frequency conversion is being energetically done for mainly high density optical memories. In Japan, the bulk type SHG devices using internal cavity resonant method with the combination of the Nd:YVO4 microchip lasers and the nonlinear optical crystal KTP are popular because the system is simple, compact and easy to get transverse and londitudinal single mode and promising for practical devices. The present status and the problems for practical use of bulk type SHG devices using Nd:YVO4, NYAB, organic nonlinear crystals and other crystals, which have being developed in Japan will be presented.
Diode Laser Upconversion in Bulk Nonlinear Resonators—An Overview of Recent Progress
Authors: Dixon G. J.
Published: February 2023

Recent progress in the fields resonant sum frequency generation and external resonant diode doubling will be discussed. The possibilities for watt-level visible devices and the issues separating bulk nonlinear devices from the commercial marketplace will be detailed.
Ho Concentration Dependence of Yb, Ho Upconversion Energy Transfer in KYF4
Authors: Zhang X.X. , Bass M. , Chai B.H.T.
Published: February 2023

We have found that the Yb → Ho upconversion process in KYF4 (KYF) is much more efficient than in either BaY2F8 or YLiF4 [1] under the same doping conditions. Long lifetime, low phonon energy, weak self-absorption, and some other unique spectroscopic features make KYF a promising host for an Yb, Ho upconversion green laser. In order to optimize the upconversion efficiency, we have carried out a detailed study on the Ho concentration dependence of the Yb → Ho transfer processes in KYF.
Low Threshold Quasi-Three-Level 946nm Laser Operation of an Epitaxially Grown Nd:YAG Waveguide
Authors: Hanna D.C. , Large A.C. , Shepherd D.P. , Tropper A.C. , Chartier I. , Ferrand B. , Pelenc D.
Published: February 2023

There has recently been much work on fabricating waveguide lasers based on crystal hosts by methods such as crystal fibre growth1, ion-exchange2, in-diffusion3, ion-implantation4, and epitaxial growth5. Despite the confinement of pump and signal beams to a few microns spot size, in general these lasers have not shown a clear advantage over bulk lasers in terms of thresholds due to propagation losses of the order of 0.1dB/cm or higher. Here we identify laser systems in which crystal waveguides will show great advantages over bulk lasers, namely 3 level and quasi-3 level transitions, and as an example describe the low threshold operation of a 946nm Nd:YAG epitaxial waveguide laser. The extra cavity loss arising from using a waveguide is less significant in (quasi-) three level systems as re-absorption loss from the lower laser level is present.
Effects of energy back transfer in Yb sensitized upconversion materials used as blue-green laser hosts
Authors: Zhang X.X. , Hong P. , Bass M. , Chai B.H.T.
Published: February 2023

Upconversion laser can potentially provide light sources in the blue-green region.
Applications of compact blue-green lasers for displays
Authors: Valley George C. , Ansley David A.
Published: February 2023

At present, the high cost, low efficiency, and complexity of blue-green lasers limit projector applications to high end products.
An All Solid-State 4.4-W Single-Frequency 532-nm Laser
Authors: Alfrey A. J. , Cheng E. A. P. , Dixon J. , Alonis J.
Published: February 2023

Recent work by Yang [1] has described high power, high efficiency generation of 532 nm radiation using the non-linear crystal Lithium Triborate (LBO) within a resonant doubler.
ZnCdSe/ZnSe MQW Laser on Tilted GaAs Substrate
Authors: Kawaguchi Y. , Ohno T. , Ohki A. , Matsuoka T.
Published: February 2023

ZnSe-related semiconductors with a wide bandgap are indispensable for blue and green semiconductor lasers, and have been extensively developed during the last few years.
Diode Laser Second Harmonic Generation in Nb:KTP to blue light
Authors: Laurell F , Cheng L.K. , Bierlein J.D.
Published: February 2023

Broad temperature and angular phasematching bandwidth, as well as high damage threshold and good homogeneity has made KTiOPO4 (KTP) the most frequently used nonlinear crystal for second harmonic generation (SHG) of 1 µm lasers to the green.
Room temperature continuous wave Er,Yb:Y3Al5O12 laser at 1.6 μm with Yb-Er pump energy transfer
Authors: Schweizer T. , Heumann E. , Heine F. , Huber G.
Published: February 2023

Er3+ lasers emitting at 1.6 μm are useful for communication and eye-safe atmospheric measurement techniques like LIDAR. In contrast to glass, the garnet crystal YAG (Y3A15O12) as a host for rare earth ions provides good thermal conductivity. The crystals used in this paper were grown in our institute by the Czochralski method. Duczynski et al.,1 reported Er: YAG laser emission at 1.6 μm pumping with a krypton-ion laser at 647 nm with a maximum slope efficiency of 12.7%. Spariosu and Birnbaum2 achieved an Er: YAG laser by exciting the upper laser level at 1.535 μm with an Er:glass laser and obtained slope efficiencies as high as 50%. Due to the weak absorption of the 4I11/2-level of Er around 965 nm (α = 0.34 cm-1 in Er(0.5%):YAG), we investigated the co-doping with Yb to enhance the pump energy absorption (see Fig. 2). Such a pumping scheme has been used in Er glasses and is particularly interesting because high power InGaAs diode lasers emitting around 970 nm are available. Figure 1 shows the relevant energy levels of Er and Yb together with the pumping mechanism and the laser transition. We used the resonant energy transfer between the 2F5/2-level of Yb and the 4In/2-level of Er by pumping into the Yb-level. The 4I11/2-level is depopulated by phonon relaxations and 2.7 μm fluorescence into the 4I13/2-level, which is the upper laser level with a lifetime of 6.5 ms in Er(0.5%):YAG. The Fluorescence spectrum of Er,Yb:YAG shows a strong fluorescence of Yb around 1 μm indicating energy back transfer from Er to Yb, when the Er-ions are excited by the 488-nm line of an argon-ion laser (see (Fig. 2). The back transfer is pronouced due to the relatively long 4I11/2 lifetime in Er:YAG.
Emission characteristics in sensitized laser crystals
Authors: Lupei V. , Lupei A. , Boulon G.
Published: February 2023

Sensitization of emission of weakly absorbing rare-earth ions in crystals by co-doping with other ions is regarded as a possible means to increase the efficiency of sold-state lasers. Requirements for the sensitizer ion (S) are a good absorption of the pump radiation and an efficient transfer to the rare-earth activator (A). Usually the systems of activator or sensitizer ions are considered as homogeneous, i.e., each member of these systems occupies identical sites, characterized by the same crystal field symmetry and strength. Moreover, in most cases a single D-A interaction mechanism is assumed.
Nd3+ laser oscillation in fluoride crystals at 1.3-μm short wavelength wing of 4F3/2-4I13/2 transition
Authors: Sigachev V. B. , Basiev T. T. , Doroshenko M. E. , Osiko V. V. , Papashvili A. G.
Published: February 2023

Nd3+-doped laser media providing gain in (1.30 ± 0.02) μm spectral region can be a potential active materials for optical amplifiers suitable for fiber-optical communication systems. Usually this spectral region corresponds to short wavelength boundary of 4F3/2−4I13/2 emission of Nd3+ ions. But the positive gain here can be suppressed because of the excited-state absorption (ESA) at the 4F3/2–4G7/2 transition. In this paper we report on the spectroscopic and laser study of a number of Nd3+ doped fluoride crystals with disordered structure in the 1.3-μm wave length region. The most promising crystalline fluorides with small ESA and positive gain in 1.3-μm telecommunication window were identified.
Recent progress in coherent lidar
Authors: Vaughan M.
Published: February 2023

Summary not available.
Application of backscatter lidar to airport traffic safety
Authors: Lönnqvist Jan , Oy Vaisala
Published: February 2023

A well established commercial application for lidar technology is cloud base height and vertical visibility measurement for airport and aviation safety purposes: Most major airports today are equipped with laser ceilometers, which are actually small, relatively low-cost, eye safe backscatter lidars.1
Pulse mode operation of a phase coupled CO2 waveguide lasers array
Authors: Lescroart G. , Muller R. , Bourdet G. L.
Published: February 2023

Phase coupled of CO2 waveguide lasers array by intracavity spatial filtering has been already reported in Ref. 1 in cw mode. The theoretical analysis for such a configuration gives a coupling efficiency larger than 70%,2 whereas the experimental measurements have been found as poor as 10%. The results discrepancy seems to be the consequence of the thermal loading of the optical elements set inside the laser cavity in which the light intensity is very large. By using a three mirrors cavity, it has been possible to reduce the power level on the optical elements resulting in an improvement of the coupling efficiency up to 66%.
Diffraction coupling of CO2-lasers
Authors: Schröder Kurt , Müller Alexander , Schuöcker Dieter
Published: February 2023

Phase-locking of two slow-flow CO2-lasers, each providing an output power of 20 W, has been investigated. The active media are situated in parallel in a distance of 55 cm to each other. Both resonators are folded twice by plane mirrors to make the two beams propagate in parallel close to each other. The laser radiation is extracted by a common semitransparent output coupler. As only reflective optics is used (except for the output coupler) this concept is also suitable for high power lasers. When the segmented folding mirror is replaced by a parabolic mirror more than two lasers can be coupled.
Magnetic control of spatial soliton interactions
Authors: Boardman A. D. , Xie K.
Published: February 2023

There is currently quite a lot of interest in spatial solitions1-3 planar optical wave guides. The first calculations, involving bright and dark solitons propagating in magneto-optic materials, will be reported. They follow up recent work of the authors, based on Lagrangian formalism. It will be shown that magneto-optic problems divide, roughly, into polar, longitudinal, and transverse configurations, according to the orientation of the magnetic field to the soliton propagation direction. The system consists of a thin nonlinear film, sandwiched between a linear, nonmagnetic, semi-infinite, cladding, and a semi-infinite, magnetic, linear substrate. It is assumed that the power levels are only sufficient to drive the film into a nonlinear state. The discussion will show that this is reasonable and that the longitudinal and polar cases are of maximum, strategic interest. Technically, both cases are controlled off-diagonal elements in the dielectric tensor, which are proportional to a parameter Q, which, when unsealed, lies between 10-2 and 10-4. Although these values seem to be quite small, in absolute terms they compete vigorously with the nonlinearity. The starting point is a derivation of a new family of coupled envelope equations; all within the familiar, slowly varying amplitude, weakly nonlinear, weakly guiding formalism. We then demonstrate, by a scaling technique, that there exists an important, magneto-optic, cross-coupling term, which can sometimes be dominant. New parameters will be introduced that will be used mathematically, and numerically, to show that, with readily available materials, an external magnetic field is a powerful control parameter. The weakness of the nonlinearity is in accord with experiment and means that the modal fields are unchanged during the accumulation of nonlinear phase and magnetic Kerr phase shifts. Both are represented, mathematically, within a Lagrangian model. In the simplest case, when the magnetisation is a constant, very simple mathematical results for bright and dark solitons flow from this novel theory. They are vindicated by the numerical experiments. Beams that are attractive to each other in the absence of a magnetic field can be turned against each other. Dark beam channels can be significantly modified and multiple beam interactions are shown to imply a new range of devices. In particular, polarisation-dependent gating devices with small beam control will be used as illustrations. A really interesting possibility is the use of a magnetisation distribution. It is possible to laser anneal doped YIG, for example, and freeze the magnetisation into different directions at different points along the boundary, thus yielding various forms of Q = Q(x).
Numerical simulations of thermal focusing and thermally induced birefringence effects in diode side-pumped Nd:YAG lasers
Authors: Ajer H. , Landrø S. , Stenersen K.
Published: February 2023

The technology of diode pumping has made possible the development of a new generation of efficient solid-state lasers. Simulation models are very useful for improving the understanding of the behaviour of such lasers, for evaluation of laser configurations, and for system optimisation.1-4 We have developed a simulation code for diode-pumped Q-switched Nd: YAG oscillators and amplifiers with both "straight-through" and zigzag slab crystal geometries.4 The model calculates the spatial and temporal evolutions of the populations in the upper and lower laser levels due to pumping, relaxations, and stimulated emission, and of the laser field due to gain, loss, and diffraction. In Ref. 4 we presented results of simulations for a 1 J/pulse system with a rod-based oscillator and a zigzag slab amplifier. We will present results for rod-based oscillators, with emphasis on effect caused by thermally induced focusing and birefringence.
Lens assemblies for multispectral camera
Authors: Lepretre François
Published: February 2023

In the framework of a contract with the Indian Space Agency (ISRO), MATRA DEFENSE-DOD/UAO have developed, produced, and tested 36 types LISS 1-LISS 2 lenses and 12 LISS 3 lenses equipped with their interferential filters. These lenses are intended to form the optical systems of multispectral cameras aboard Indian earth observation satellites IRS 1A, IB, 1C, and ID. It should be noted that the multispectrum cameras of the IRS 1A-1B satellite have been in operational orbit for two years and have given very satisfactory results.
Quantum well lasers with lateral Bragg reflectors
Authors: Yang F. , Blood P. , Roberts J. S.
Published: February 2023

We have studied quantum well (QW) laser diodes grown with a pair of Bragg reflectors acting as cladding layers. The high reflectance band of each Bragg structure is designed to be spectrally coincident with the spontaneous emission of the QW, while the resonance of the Fabry–Perot etalon consisting of the two Bragg reflectors is outside the high reflection band of each Bragg reflector and the spontaneous emission band of the QW. In such a structure, spontaneous emission normal to the laser cavity is inhibited because of the lack of modes at the corresponding wavelengths, and therefore the threshold current should be reduced.
Spectral broadening by carrier-carrier scattering in quantum well gain-current calculations
Authors: Rees P. , Blood P.
Published: February 2023

The large number of carriers injected into a semiconductor laser near threshold means that their interaction with one another is an important consideration in the modelling of gain-current characteristics. Carriers remain in their energy states a finite amount of time due to the scattering with other carriers and phonons. There is then an associated broadening of any radiative transitions involving these states. Several theoretical studies of the scattering rates and the associated energy broadening of the electron states have been performed. The broadening of the states is found to be dependent on the carrier population and on the energy of the state, although the majority of calculations of radiative recombination spectra have included a constant energy broadening.
Micromachining by lasers
Authors: Schmidt H.
Published: February 2023

The continually increasing demand for miniaturisation in the fields of electronics, micro-system-technology, and microoptics leads to higher and higher requirements for micromachining tools. Lasers are ideal for micromachining of metals, ceramics, and polymers. UV radiation of excimer lasers and frequency-quadrupled Nd:YAG-lasers with short pulses of 10 ns to 150 ns, and intensities up to 109 W/cm2, allow machining with sub-micron structure size and minimal thermal influence. The high photon energy of UV laser radiation facilitates a direct photolythic interaction with some materials. Besides this, thermal and pyrolytic interaction mechanisms also appear. Regarding this, removal mechanisms of certain materials depending on laser properties are discussed. Handling-systems for micromachining are as important as the laser itself. The application of excimer laser radiation in a multiaxis CNC-micromachining unit with modular design is presented. Special features of this micromachining centre are the beam handling system with integrated flexible mask and energy control. The workpiece handling and all process parameters are controlled by a host computer with a user-friendly interface. The unit can be used to generate microstructures in micromechanical parts and ceramic and polymer surfaces with a resolution of 1 pm horizontally, and 0.1 μm vertically. In this way, it is possible to produce, e.g., microlenses in glass or polymers.
Phase conjugation of short pulse Nd:YAG solid state lasers
Authors: Valley M. , Injeyan H. , Pierre R. St. , Clendening C. H. , Lembo L.
Published: February 2023

Phase conjugation by stimulated Brillouin scattering (SBS) is now a common technique for producing high-brightness output from short pulse solid-state lasers. Near diffraction-limited beam quality has been demonstrated by the 100 W level, and scaling to the kilowatt level1 is in progress. Obtaining high brightness using SBS requires an interplay between the SBS subsystem and the overall laser design.
OSBS phase conjugation for high-power solid state lasers and amplifiers
Authors: Menzel Ralf , Haase Andreas , Geinitz Eckart , Eichler Hans J.
Published: February 2023

High-power solid state lasers show usually bad beam quality of more than ten times diffraction-limited. The distortions are generated by the thermally induced lensing and birefringence in the active material. Phase conjugating mirrors based on stimulated Brillouin scattering (SBS) can be applied for improving these lasers up to the theoretical limit. Particularly, these new elements allow the construction of highly pumped lasers with diffraction-limited beam quality with inexpensive laser rods instead of slabs.
Multiple wavelength interferometry for distance measurement
Authors: Dändliker René , Hug Kurt
Published: February 2023

The interferometric measurement at different, well-known optical wavelengths allows the generation of new synthetic wavelengths, which are much longer than the optical wavelengths. For two wavelengths λ1 and λ2, one obtains the synthetic wavelength Λ = λ1λ2/|λ1–λ2|. This method thus allows to increase the range of unambiguity for interferometry and to reduce the sensitivity of the measurement.1 In order to obtain this new, synthetic wavelength, the different optical wavelengths (which do not interfere) have to be interrelated. Real-time electronic signal processing is mandatory for practical applications.
Noncontact characterization of surface coating adhesion by laser-generated acoustic waves
Authors: Weiss P. , Sigrist M. W.
Published: February 2023

The adhesion strength of surface coatings is a crucial parameter in view of the performance of such coatings. We present a noncontact technique that permits a quantitative characterization of the coating adhesion. It is based on laser-induced acoustic waves and interferometric detection of the generated transient surface displacement. Nd:YAG laser pulses are used to generate the required acoustic pulses at the back side of the sample. The solid coating at the front surface of the sample will undergo delamination if the superposition of the generated incoming compressive and of the reflected tensile wave exceeds the adhesion strength of the coating. The time-resolved monitoring of the coating displacement yields information on the adhesion properties. The transient surface displacements are measured with a specially designed, homodyne fiber-optic interferometer. It enables the detection of displacements of >1 nm at a large bandwidth of 300 MHz.1 Furthermore, an analysis software has been developed that allows an interactive calculation of the time-dependent displacement from the interferometer signal. Here we present new results obtained for plasma-sprayed Cr2O3 and Mo/Mo2O3 layers on steel substrates. An example is shown in Fig. 1 for a 120-μm-thick molybdenum ceramic layer. Seven consecutive laser shots were fired onto the same spot on the rear side of the steel substrate. Figure 1(a), shows the interferometer signals and Fig. 1(b), the corresponding calculated displacement signals of the molybdenum layer opposite the laser impact for the first three shots. Obviously the first shot (numbered 1) produced a delamination of the layer with a gap of ≈ 1 μm remaining between substrate and layer. Because of this delamination gap, the longitudinal acoustic pulses generated by further laser impacts cannot reach the on-axis detection point directly but only by circumventing the gap by its still adhering rim. The resulting extension of the path explains the observed delay of the arrivals of signals 2 and 3. The delay of approx. 20 ns (Fig. 1(c)) corresponds to a lateral diameter of the delamination of 320 μm. Although this delamination can clearly be detected, the surface of the ceramic layer does not show any visible damage. This demonstrates that conventional, e.g., microscopic inspection of the surface is not an adequate means to detect the delamination of coatings while our technique is capable of producing and detecting minute delaminations. Further examples for nickel-coated steel samples will be presented, including detailed analyses of the interferometer signals in view of the adhesion strength of these coatings.
Integrated optical heterodyne interferometers in LinbO3
Authors: Sohler W.
Published: February 2023

Summary not available.
Infrared tunable sub-100 fs pulses of gigawatt peak power at 1 kHz by parametric conversion of CPA Ti:sapphire laser radiation
Authors: Nisoli M. , De Silvestri S. , Magni V. , Svelto O. , Varanavicius A. , Danielius R. , Piskarskas A.
Published: February 2023

High-energy femtosecond pulses tunable in a wide spectral region of the infrared are strongly needed for a variety of applications in nonlinear optics and spectroscopy. Optical parametric conversion has been demonstrated to be one of the most effective techniques for the generation of tunable ultrashort pulses due to the recent achievements in solid-state pump lasers and highly nonlinear crystals. In the case of low-energy femtosec­ond pulses synchronously pumped optical parametric oscillators have been extensively investigated.1,2 For the generation of high-energy tunable pulses, a traveling wave parametric conversion seems to be the most favorable technique.3,4
Upconversion fibre lasers
Authors: Wyatt R.
Published: February 2023

Summary not available.
Modification of ceramic surfaces by excimer laser processing
Authors: Becker W. , Hutfless J. , Geiger M.
Published: February 2023

Over the last few years a lot of work has been published on structuring all kinds of polymers and ceramics by excimer laser radiation.1,2,3 But excimer laser radiation can also be used to modify ceramic surfaces, e.g., to reduce the surface roughness of various engineering ceramics.4 This method is a new, versatile, and efficient alternative to conventional ways of surface finishing of ceramics with expensive diamond tools.
Phase conjugation of orthogonal polarized laser beams in inverted Nd:YAG-rod
Authors: Antipov O. L. , Belyaev S. I. , Kuzhelev A. S.
Published: February 2023

It is well known that inverted laser crystals have a strong inertial optical nonlinearity that is connected with changing of susceptibility by saturation of laser transition. The phase conjugation (PC) of laser beams by parametric oscillation in resonator with holographic mirror induced by means of mutually-coherent pumping waves in an inverted laser crystal was discussed.1,2 In our work, the phase conjugation of laser beams in loop scheme with an inverted Nd:YAG-rod (where two near-counter-running light beams with orthogonal polarization intersected) was investigated.
Environmental analytical chemistry and optical sensors
Authors: Niessner Reinhard
Published: February 2023

Applications of laser spectroscopy for highly sensitive detection of harmful substances are demonstrated.

• Laser-induced, time-resolved fluorescence applied to aerosol and water. Analytes of interest are polycyclic aromatic hydrocarbons and geological tracer substances. Detection limit is around 10 ppt.

• Laser-induced breakdown spectroscopy for rapid screening of the elemental content of soil, sand, and landfill barrier. The various parameters for signal formation are discussed. Detection limit is around 10 ppm for selected heavy metals.

• Resonant photoacoustic detection of free-flowing particles. Via a modulated diode laser the true light absorption by ultrafine carbon particles is measured in situ. Common to all techniques is proportionality of signal versus laser power. In the case of laser-induced fluorescence the construction of fiber-optical sensors is possible. First applications to real matrices are presented.
Chirped multilayer mirrors for dispersion control of femtosecond pulses
Authors: Spielmann Ch. , Stingl A. , Krausz F. , Szipöcs R.
Published: February 2023

Standard femtosecond self-mode-locked oscillators contain a pair of Brewster-angled prisms for producing a net negative group-delay dispersion (GDD) in the resonator. Prism pairs have been widely used for intracavity dispersion control in dye systems and adopted for the new generation of solid-state short-pulse lasers. Extensive theoretical and experimental research revealed that cubic phase dispersion introduced by the intracavity prism pair is the dominant factor limiting the minimum achievable pulse width in ultrafast solid state lasers. This finding prompted search for prism materials exhibiting low cubic phase error and led to the construction of fused-silica-prism-controlled Ti:sapphire lasers,1 which are capable of generating pulses down to 11/s in duration.2
Discharge uniformity control in kilowatt class, rf excited, large area electrode CO2 lasers
Authors: Colley A. D. , Vitruk P. P. , Doyle L. A. , Baker H. J. , Hall D. R.
Published: February 2023

RF discharge excited waveguide gas lasers using diffusion cooling require a high excitation frequency in excess of 100 MHz to achieve stable discharges and high power output from an ultra-compact laser head.1-3 As a consequence, longitudinal non-uniformity of the RF discharge voltage occurs along the RF electrodes due to transmission line effects, for simple, centre-fed parallel plate electrode structures. Traditionally, uniformly loaded transmission line theory4 has been used to model the longitudinal voltage distribution along a single pair of RF electrodes whose length is limited to about 1/8 of the EM-wavelength at the excitation frequency.1'2 Recently, we have developed a slab waveguide CO2 laser producting over 1 kW output, where the electrode length approaches one-third of the EM-wavelength.5 The achievement of discharge uniformity with a single RF feed to the device becomes a major issue in the successful operation of the laser, and a fuller understanding is needed of the mechanisms controlling uniformity.
Kilowatt single transverse discharge excited slab waveguide array CO2 laser
Authors: Xin Jian Guo , Wei Guang Hui , Zhang Jin Wu , Xu Ling Yun , Dong Hong Chuan
Published: February 2023

In the past decade, RF transverse discharge excited diffusively cooled CO2 lasers have experienced the advances from single-channel and folded-channel structures to waveguide array devices in aiming to obtain compact size and high quality beam. In recent years, an area scaling technique with the advantage of simplicity has been reported, which makes use of the slab waveguide large area RF discharge uniform excitation and an optical unstable resonator, and combines the diffusive cooling to make the compact kilowatt CO2 laser into reality. In this paper, we shall present a new technique, single RF discharge excited diffusively cooled 1 × 2 slab waveguide linear array CO2 laser, with which we have obtained over 1 kilowatt power output. In this type of laser structure, the electrode length is only 500 mm, and each array element has a cross section of 99 × 2 mm2. In experiments, the whole waveguide array is excited by a single RF input, and the RF frequency is 93 MHz. The gas mixture pressure is 70 torr with composition of CO2:N2:He:Xe = 1:1:3:5%. The output beam dimension of each array element is 2×16 mm2. In the far field, the two beam spots overlap and are combined into a single peak distribution. Experiments have shown that it is possible to use this technique to produce multikilowatt high beam quality power output from a compact-sized device.
Wide band, fine tuning of a TEA CO2 laser by means of intracavity active frequency shift
Authors: Suda Akira , Tashiro Hideo
Published: February 2023

High-pressure CO2 lasers are capable of producing intense beams with continuous frequency tunability in the 9µm and 10µm bands. The linewidth, however, amounts in general to several GHz with multilongitudinal-mode oscillations.1 Although injection locking is widely applied to narrow the linewidth in various lasers, this technique is effective only at the wavelength near the line centers in the high-pressure CO2 lasers because of the lack of a suitable master oscillator for providing tunable injection beams.
Limiting effects in densely doped erbium amplifiers
Authors: Jaskorzynska B. , Nilsson J.
Published: February 2023

Optical fibers and planar waveguides doped with erbium ions offer numerous attractive features for use as amplifiers or lasers in the important communication window around 1.5µm. An important aspect for the realization of practical amplifiers is the achievement of a high gain at a reasonable pump power, i.e., the gain efficiency should be high. In a standard erbium-doped fiber amplifier (EDFA) of typically a few meters length and with a moderate erbium concentration (<1000 ppm), gains larger than 30 dB and gain efficiencies of a few dB/mW can be readily achieved.
Photosensitivity in germania-doped silica films
Authors: Poulsen Christian V. , Svalgaard Mikael , Poulsen Ove
Published: February 2023

Integrated optics is believed to be the key technology for future integrated optical systems. One standard method for processing planar waveguides is a combination of plasma enhanced chemical vapor deposition (PECVD) for growing glass layers and photolithography/reactive ion etch (RIE) for creating the waveguides2 (Fig. la). We present an investigation of the photosensitivity of germania-doped silica films. The results may lead to an alternate method for creating the guiding structure in planar waveguides that requires much fewer process steps. Instead of using a combination of photolithography and RIE for defining the guiding core, the index change due to photosensitivity of germanium-doped silica may be utilized (Fig. 1b). To investigate the photosensitivity, germanium-doped silica films were grown on a 4" silicon wafer in a PECVD chamber. These films were fabricated at a temperature of 300°C, a base pressure of 700 mTorr, and gas flows of 17 seem silane, 1600 sccm nitrousdioxide and up to 8 sccm germane followed by annealing at 800°C in a nitrogen atmosphere for two hours.
A diode-pumped, first window optical fibre amplifier providing up to +12 dBm of output
Authors: Lauder R. D. T. , Tropper A. C. , Hanna R. M. Percival D. C. , Szebesta D. , Wyatt R.
Published: February 2023

The thulium ion is one of great interest when it is doped within fluorozirconate glass due to the number of transitions available for stimulated emission. One such transition is the 3F4 to 3H6 transition at 0.8µm. This is of interest as it lies within the first window for optical communication. There is growing interest in the use of this window for local area networks, passive optical networks, or supervisory systems. Small signal amplification of up to 23 dB has been reported for this transition in a thulium-doped fluoride fibre using a Ti:sapphire laser as the pump source.1 We report here the first diodepumped operation of this optical amplifier. An intrinsic small signall gain in excess of 30 dB was achieved. With a launched 807-nm signal power of -10 dBm, intrinsic gain of 21 dB was observed, producing amplified output powers of +11 dBm. An intrinsic gain of greater than 20 dB was observed for signals over the spectral range of 802 nm to 810 nm. The greatest amplified output power obtained for this system was 12.8 dBm for 30 mW of launched diode pump power.
Diffractive elements with large diffraction angles
Authors: Bräuer Ralf , Bryngdahl Olof
Published: February 2023

Diffractive elements such as digital holograms1 and Dammann gratings2 can be used to generate an array of diffraction orders with specified intensity. The part of the diffraction pattern that contains these orders is called the signal window. The elements are designed using scalar diffraction theory; i.e., geometrical optics is used to predict the transmitted or reflected wave-front, and the wave propagation outside the element is calculated by paraxial approximations. For scalar diffraction theory to be valid the features of the element must be large compared to the wavelength. Correspondingly, the grating periods are large and the diffraction angles are small; the elements operate in the paraxial domain. The maximum diffraction angle within the signal window can be estimated via the knowledge of the number of features necessary to realize a specified optical function and the minimum feature size; 5° results as an upper limit. A more flexible choice of the diffraction angles may broaden the scope of possible applications of diffractive elements. Fortunately, the limit is not a general one within the frame of diffractive optics.
Two-photon excited fluorescence microscopy using spectroscopic detection techniques
Authors: Andersson-Engels S. , Rokahr I. , Carlsson J.
Published: February 2023

Fluorescence microscopy in combination with spectroscopic detection is a powerful tool for simultaneously studying several independent fluorophores in a sample. In medicine, such a tool is interesting for studies of the localisation of various photosensitisers in the development of photodynamic therapy. In these studies one needs to be able to measure the weak signal from a sensitiser without any interference from the tissue autofluorescence. Also, it is interesting to measure the fluorescence emission characteristics as they shift with the local environment of the sensitiser. Two-photon excited scanning fluorescence microscopy is interesting for such studies, due to its simplicity and straight forward compatibility with temporally or spectrally resolved detection techniques. An advantage of two-photon excited fluorescence microscopy, compared with conventional fluorescence microscopy is that the excitation is made only in the small volume defined by the focus of the laser beam. This directly gives a high three-dimensional spatial resolution.
Fluorescence studies using time-resolved multispectral methods
Authors: Stavridi M. , Grundfest W. S.
Published: February 2023

Steady-state and time-resolved fluorescence have been approached as two different methodologies in fluorescence studies. The fact is that both have been applied successfully to study the physical properties and as a fingerprint to differentiate among various physiological states.1 3 We wanted to combine both techniques in one design and have the advantage of simultaneously acquiring both static and dynamic fluorescence characteristics of the compounds under examination. We introduce a method for the acquisition of both spectral and temporal fluorescence emission from tissue chromophores after monochromatic excitation.
A single head 1.4 kW Nd:YAG slab laser with lamp pumping
Authors: Seguchi Masaki , Kuba Kazuki , Ishimori Akira , Yamamoto Takashi
Published: February 2023

A Nd:YAG slab laser is a promising candidate for material processing as it has potential of producing a high-power beam with good focusability. The maximum power of a single head Nd:YAG slab laser has been around 1 kW because of optical distortion induced in the laser medium. We have developed a lamp pumped, single head 1.4 kW Nd:YAG slab laser. A Brewster angle Nd:YAG slab (6 × 25 × 213 mm3, 0.8 AT.% doping) is used. The number of total internal reflections of the laser beam in the slab medium is 20. The slab is pumped over a length of 150 mm by four krypton arclamps with the arc length of 6 inches and inner diameter of 7 mm.
Time resolved reflectance
Authors: Svaasand L. O. , Tromberg B. J. , Haskell R. C.
Published: February 2023

Recent demand for rapid and non-invasive diagnostic techniques in medicine has initiated an extensive research in the field of optical diagnostics. Reflection of light from biological tissue is a typical multiple scattering phenomenon. The backscattered light from an incident short optical pulse will be broadened in time, and this broadening can be mathematically related to the large number of optical paths available in multiple-scattering media. Since the introduction of losses (absorbers) reduces the average path length, absorber-dependent changes in pulse propagation time can be used to calculate absorption coefficients. In contrast to continuous illumination techniques, pulse propagation methods can provide information on the distribution of scatterers and absorption in a single measurement.
Copper lasers and materials processing—an overview
Authors: Kearsley A. J. , Knowles M. R. H. , Foster-Turner R. , Errey K. H.
Published: February 2023

The copper laser is a pulsed visible laser (511 and 578 nm laser lines), which emits intense (50-500 kW), short pulses (20-60 ns) at high pulse repetition frequencies (2-32 kHz). Average powers from commercial units range from 10-120 W whilst laboratory devices have reached over 750 W. Beam quality in the past has been rather poor but recent developments in resonator design and amplifier configurations has resulted in beam qualities near the diffraction limit. MOPA systems have been constructed with powers in excess of 2 kW. This set of laser parameters is unique and offers particular advantages for certain areas of materials processing.