High-power broad-area diode lasers for laser cooling

Received: 1 April 1996/Revised version: 24 September 1996     

Ultrafast ytterbium-doped bulk lasers and laser amplifiers

We review recent achievements with ultrafast bulk lasers and amplifiers based on Yb:YAG and Yb:glass. Special attention is paid to those aspects of the quasi-three-level nature of these gain media that are important for short-pulse generation. The potential of Yb-doped media for efficient short-pulse generation and amplification is compared to their Nd-doped counterparts. Received: 4 January 1999 / Revised version: 15 March 1999 / Published online: 26 May 1999     

Generation of Laguerre–Gaussian modes in fiber-coupled laser diode end-pumped lasers

A technique has been developed for the generation of Laguerre–Gaussian (LG_0,l) modes in a fiber-coupled laser diode end-pumped microchip laser. A theoretical model is also developed to predict how the oscillation of LG_0,l modes is affected by the pump position, the pump size and the cavity mode size. With a 1-W fiber-coupled diode, the highest-order LG_0,l mode that can be generated is l=23. Received: 8 June 2000 / Revised version: 2 July 2000 / Published online: 20 September 2000     

Excimers and excimer lasers

The development of excimers and excimer lasers are reviewed. The excimers of the noble gases (Xe ₂ ^* , Kr ₂ ^* , Ar ₂ ^* ) and of the noble gas halides (e.g. KrF, XeCl) which, respectively, radiate in the vacuum ultra-violet and ultra-violet regions of the spectrum are described in terms of their structure, spectroscopy and formation kinetics and the methods of pumping, operational characteristics and applications of the lasers are discussed.     

New UV tunable solid-state lasers for lidar applications

We present the first lidar/DIAL system based on an Ultra Violet (UV) vibronic laser. A Nd:YAG-pumped Ce:LiSAF laser has been developed for this purpose, providing high pulse energy (5 mJ at 10 Hz), very high slope efficiency (33%), and a tuning range from 284 to 299 nm. Simultaneous measurements of SO₂ and O₃ concentration profiles are presented using this frequency-agile Ce:LiSAF-based lidar system.     

FM dye lasers

We have investigated the detailed operation of a frequency modulated dye laser (FML). The FML consists of a standing wave Rh6G dye laser with an intracavity transverse ADP phase modulator which is driven at a frequency close to the cavity mode spacing. An ideal FML output consists of a laser beam which is constant in amplitude but sinusoidally varying in frequency. This provides a source of many laser modes which are equally spaced by the modulation frequency. Several dye laser configurations have been investigated. Measurements of the mode intensities, total power, amplitude modulation and rf beat amplitudes have been made as a function of the rf driving frequency of the phase modulator. The FM laser obtained has been frequency stabilised by locking it to a reference interferometer and also by frequency offset locking it to a single-frequency dye laser.     

Precise rf tuning for cw dye lasers

Laser beams are rf amplitude modulated to generate side frequencies which are used to tune a cw dye laser with rf accuracy. In a laser spectroscopic test experiment a precision of ±15kHz has been realized.     

300 Femtosecond pulses at 497 nanometer generated by an excimer laser pumped cascade of distributed feedback dye lasers

The setup is a cascade of 3 lasers: A competing cavity dye laser pumped by a XeCl excimer laser, followed by two distributed feedback dye lasers. The typical durations of the pulses from the lasers are 100 ps, 5 ps, and 300 fs, respectively. The output pulses at 497 nm are amplified up to 500 MW. The shortest pulse duration obtained was 198 fs.     

Influence of spatial mode matching in end-pumped solid state lasers

We present investigations on the influence of mode matching on the efficiency of longitudinally pumped solid state lasers. In a theoretical part we enhance an existing model for four level lasers from idealized cylindrical modes to arbitary pump and laser modes in a random relative position thereby neglecting beam deformation due to thermal effects. The theoretical predictions were confirmed experimentally with an end-pumped Nd:YAG rod operated at 1064 nm. To investigate the effect of misalignment on the efficiency we used a Ti-Sapphire pump laser which was displaced relative to the laser beam. To establish the influence of arbitary pump modes on laser performance a diode laser equipped with coupling optics served as pump source for the same resonator. The resulting decrease in slope efficiency compared to the Ti-Sapphire pumped system could be explained in terms of limited mode overlap due to the characteristic pump field distribution produced by the diode coupling optics.     

On the pulse width of synchronously pumped lasers

The pulse width of a synchronously pumped laser chiefly depends on the available cavity bandwidth and the pump-pulse duration. A functional form of this dependence was suggested in the literature. We present an alternate relation which is supported by analytical and numerical results, as well as by experimental results, obtained by us and by others.     

Mode-locking dynamics of synchronously-pumped colour-centre lasers

A theoretical model has been developed for studying the steady-state pulse shaping dynamics of a synchronously-pumped colour-centre laser. A wide range of results is presented detailing effects on the mode-locking process of pump pulse power and width, laser bandwidth, cavity mismatch and, stochastic noise. From the results, we identify conditions which lead to the formation of single and multiple pulses. We show this can be understood on the basis of a simple scaling law between the principal laser parameters.     

New short-wavelength laser emissions from partially deuterated methanol isotopes

The partially deuterated isotopes of methanol, CH₂DOH and CHD₂OH, have been reinvestigated as sources of far-infrared (FIR) laser emissions using an optically pumped molecular laser (OPML) system recently designed for wavelengths below 150 μm. With this system, 10 new FIR laser emissions from these isotopes ranging from 32.8 to 174.6 μm have been discovered. This includes the shortest known OPML emission from CHD₂OH, at 32.8 μm. These lines are reported with their operating pressure, polarizations relative to the CO₂ pump laser and wavelengths, measured to ±0.5 μm. In addition, polarizations for three previously observed FIR laser lines from CHD₂OH were measured for the first time. This paper is dedicated to the memory of Dr. K.M. Evenson, a pioneer in the field for his role in the development of optically pumped molecular lasers and their use in laser frequency measurements and the laser magnetic resonance technique. His scientific expertise, guidance, mentoring and friendship will be greatly missed. Received: 27 March 2002 / Published online: 8 May 2002     

Peltier cooled PbSe double-heterostructure lasers for IR-gas spectroscopy

PbS−PbSe−PbS double-heterostructure lasers have been pulse-operated at about 200 K mounted on 4 stage thermoelectric coolers. Emitting at a wavelength of about 5.5 μm they could be used for NO gas spectroscopy. Operation temperatures of up to 230 K have been achieved with structures consisting ofn-type PbS substrates and epitaxial layers ofn-type PbSe and Tl dopedp-type PbS. The temperature dependence of the threshold current density and the emission wavelength of these DH-lasers was compared with PbSe-homojunction lasers. The use of a germanium etalon for a quick evaluation of the spectral quality of the emitted radiation is described.     

Realizable free-electron lasers

We analyze the general class of constant period free-electron lasers (FELs) based on single-pass linear accelerator technology. The emittance and energy spread of the electron beam used to drive an FEL must be chosen to match the acceptance of the FEL wiggler. This acceptance determines the attainable current, and the current determines the gain and power output. For an optimized system in which the optical mode size in the interaction region is minimized, the gain is found to be independent of the laser length, while the efficiency and power output scale as the inverse and inverse cube of the length. Very high power output and good efficiencies are predicted.Work supported by the Office of Naval Research     

A new simple model for high-power pulsed gas lasers

An analysis of a modified electrode geometry for pulsed gas-laser excitation circuits, generating shorter excitation pulses than those normally obtained, is reported. Results from an atmospheric N₂ laser obtained with this electrode geometry are compared with others available in the literature.Paper partially presented at the XIII Intern. Quantum Electronics Conf., Los Angeles, CA, USA (1984)     

Standard and phase-matched grazing-incidence and distributed-feedback FIR gas lasers

In this paper we review theoretical and experimental studies on optically pumped 496 m CH₃F DFB lasers of different configurations, including grazing-incidence arrangement and phase matching by a gap in the periodic structure. These configurations combine the simple tuning mechanism of grazing-incidence systems with the high frequency selectivity of DFB. Our theoretical considerations based on coupled-wave theory are concerned with the dispersion relations and resonance conditions of standard and phase-matched DFB and grazing-incidence gas lasers. We have succeeded in calculating the relevant TM coupling coefficients for lasers with rectangular periodic waveguides. For laser cavities with various continuous gratings we have measured the resonant heights and tuning angles of the laser oscillations of first- and second-order DFB. We have found good agreement with theoretical resonance conditions. In order to improve the mode selectivity and to attain single longitudinal mode operation, which is a requirement for semiconductor lasers in many applications, we have introduced variable gaps in the center of the gratings. These provide phase matching and gap modes. We have compared the measured gap modes with our theory and found agreement in specific cases, where the phase-matched cavity implies single-mode laser operation. Our results on standard and phase-matched DFB cavities promise an improvement of the performance of phase-matched semiconductor lasers with respect to small bandwidth and optimized output power.     

Planar dye lasers in isotropic and anisotropic oriented media

Planar dye lasers in isotropic and anisotropic media are described. Isotropic structures supporting real modes are considered as well as leaky modes. The anisotropic structure is obtained with an oriented liquid crystal which can be made to lase in both the nematic and smectic phase.