High power,high efficiency optically pumped NH3 lasers

A simple and efficient NH₃ laser was tuned over more than 70 vibrational band transitions between 10.08 and 14.14 m. The active medium was a dilute mixture of ammonia in argon and was optically pumped by the 9R(30) transition of a pulsed TEA-CO₂ laser. Output energies greater than 1 J per pulse were observed on several of the strongest lines. In a non-selective cavity an energy conversion efficiency of greater than 35% was obtained with a maximum output energy of 4.6J. Optically pumped NH₃ is shown to be a flexible and efficient system for the downconversion of CO₂ radiation.     

Modeling of high-pressure 12-μm NH3 lasers

Experimental measurements of small-signal gain in an optically-pumped NH₃ amplifier are carried out at pressures ranging from 40 Torr to 760 Torr, and the results are used to validate a rate-equation model describing the amplifier dynamics. The gain measurements show that dilute mixtures of <0.5% NH₃ in N₂ are reqired to minimize the problems of gas heating due to pump absorption. The model is used to extrapolate the results to gas pressures of several atmospheres, and to demonstrate the potential for highpressure operation of optically-pumped NH₃ lasers. For a pump intensity of 100 MW/cm², calculations indicate that operation of an NH₃–N₂ laser is feasible up to a pressure of 10 atm, which would provide a maximum continuous tuning range of 4 cm^–1. High-resolution spectroscopy reveals that gain on a few NH₃ transitions is eliminated at high pressures due to the presence of overlapping absorptions in other NH₃ bands.     

Relaxation oscillations in cw optically pumped CD3OD and15NH3 lasers

We report the results of heterodyne measurements of the mode quality and tuning range of a cw CO₂ laser designed for optically pumping a far-infrared (FIR) molecular laser, and describe the implications of multi-mode operation. In particular we report the observation of relaxation oscillations in the output of a FIR waveguide laser.     

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.     

Theory of passively mode-locked cw dye lasers

The circulation of an ultrashort light pulse in a continuously pumped modelocked dye laser with a linear cavity configuration containing the active dye, the saturable absorber and a bandwidth-limiting elements is treated. The steady-state condition that the pulse shape reproduces after each cavity round-trip leads to a nonlinear integro-differential equation for this pulse shape. An approximate method for the solution of this equation not limited to the case of low laser gain and small pulse energies is given. The stable single pulse region and characteristic pulse parameters, as energy, duration, intensity and asymmetry, are considered in dependence on the laser parameters.     

Operation of KrF and ArF tunable excimer lasers without Cassegrain optics

A commercial tunable excimer laser consists of an oscillator-amplifier combination. The oscillator produces high-quality light that is sent to the amplifier and is distributed throughout the amplifier cavity via Cassegrain optics. We describe here two alternative approaches, a single-pass configuration for use with KrF and a triple-pass configuration with ArF, both of which do away with the Cassegrain optics. In each approach, the beam energy is the same as with Cassegrain optics. For KrF, the changes provide better locking, a higher degree of linear polarization, and a better spatial beam homogeneity, but a poorer beam divergence. For ArF, there is also better beam homogeneity, but the locking efficiency and divergence are not as good as with Cassegrain optics.     

Injection locking of ArF excimer lasers

Injection-locking characteristics of an ArF excimer oscillator-amplifier laser are described including the use of stable-unstable optical cavities. Output intensities of 1 MW cm^–2 have been produced with 3 mJ output energy, a spectral linewidth better than 5×10^–3 nm and an injection locking efficiency of 0.9.     

Diode-pumped colour-centre lasers tunable in the 1.5 µm range

Under pumping with a 990 nm, 1 W laser diode, continuous-wave (cw) tunable laser emission in the 1.5 µm wavelength range was obtained from two different colour centres: Tl⁰(1) in NaCl:Tl⁺ and (F ₂ ⁺ )_H in NaCl:OH^–. The results are compared to those recently obtained with a similar apparatus and Tl⁰(1) centres in KCl:Tl⁺. The highest output power (30 mW) and the broadest tuning range (1.48–1.68 µm) were achieved with (F ₂ ⁺ )_H centres.     

Preionization and discharge stability study of long optical pulse duration UV-preionized XeCl lasers

This paper presents a complete study of the temporal and spatial characteristics of the preionization of a XeCl rare-gas halide laser. The detailed study was made possible using the technique of laser-induced preionization which utilizes the uv radiation from a KrF laser to preionize a second rare-gas halide laser. In addition to the preionization study, high spatial and temporal resolution framing camera photographs have been used to investigate the growth of discharge instabilities which can lead to the premature termination of the XeCl optical pulse. The roles played by HCl, Xe, the buffer gas as well as the discharge energy loading in the development of discharge instabilities have been determined experimentally.     

High-brightness ultraviolet excimer lasers

At present the performance of short-pulse rare-gas-halide excimer-laser systems is definitely below that of solid-state systems, as far as the maximum peak-power is concerned. However, short-pulse excimer lasers are expected to be the best candidates to produce the highest focused intensities (I 10²⁰ W/cm²) provided by the shorter wavelength and less optical distortion in the gaseous active medium. This is especially feasible if the present performance of short-wavelength focusing optics is improved, and the problem of the limited extraction efficiency of excimers is solved. In this paper the results of former developments, novel methods, such as spatially-evolving chirped-pulse amplification, off-axis amplification, interferometric multiplexing, and some considerations for the achievable maximum brightness of table-top excimer systems are presented.     

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     

High-power tunable IR Raman lasers

Physical principles, new ways and means of creation, schemes, characteristics and features of efficient high-power tunable pulse Raman lasers, operating in the near and middle ir are reviewed. The paper includes: tunable dye and Nd lasers as pump sources; promising active media and their optimal excitation methods; optical systems for producing spatially homogeneous pumping; the physics of Raman oscillators and their practical schemes, efficient high pulse energy liquid N₂ and compressed H₂ Raman oscillators, covering several bands in the range between 1.4 and 9.2 μm; the physics and construction of efficient tunable Raman amplifiers-convertors, amplifying in the saturation regime of spontaneously scattered or beforehand produced and collimated external Stokes signals, obtained in the spectral range between 0.83 μm and 18 μm. Raman laser using a, so-called, broadband pump where the linewidth of pumping light is broader than the spontaneous scattering linewidth, are also discussed. Features of both amplification and oscillation regimes of such broadband pumped Raman lasers are reported, and conditions for the efficient frequency conversion are determined.     

Multimode coupling and nonlinear-gain effects in distributed and helical feedback gas lasers

We present a detailed experimental and theoretical study on the waveguide modes of distributed feedback (DFB) and helical feedback (HFB) gas lasers including for the first time the experimental verification of multimode-coupling and nonlinear-gain phenomena. For this purpose we used oversized hollow metal waveguides with periodic or helical corrugations. The latter exhibit the symmetry of either the single helix or the double helix. For the interpretation of our observations we developed a coupled-wave theory extended to multi-mode coupling and adapted the nonlinear-gain approach for strong coupling by Haus. The experiments with DFB and HFB gas lasers give new relevant information on these phenomena.On leave from Academia Sinica, Beijing, People's Republic of China     

Spectral properties of diode-pumped non-planar monolithic Nd:YAG ring lasers

The coherence length of a single-frequency monolithic Nd:YAG ring laser is determined by using a highly unbalanced all-fiber Mach-Zehnder interferometer. A coherence length larger than 1500km and a 3 dB linewidth less than 60 Hz is estimated.Furthermore, an easy method to measure the temperature dependence on several laser parameters is described. This method is based on the laser emission in multiple axial modes, which is enforced by coherent optical feedback. A model explaining the multimode behaviour is presented.     

Performance of internal-mirror frequency-stabilized He-Ne lasers emitting green,yellow or orange light

A comprehensive control system has been developed for the stabilization of internalmirror He-Ne lasers to their power envelopes. It is designed particularly for use with lasers emitting at 552, 505, or 490 THz (543, 594, 612 nm). The aim has been to combine convenience in routine operation with good day-to-day resettability and minimal frequency drift during a day. The lasers are observed to emit in up to four modes simultaneously and their tuning behaviour is highly alignment-sensitive. They also tend to flip between modes having orthogonal linear planes of polarization. Reliable control of polarization and mode frequency are possible using permanent magnets and active length control through thermal expansion. The stabilized single-frequency outputs have frequency drifts of about 2×10^–8 per year, and powers of between 150 W and 850 W.     

Self-focusing and defocusing of TEA CO2 laser radiation in NH3

We report on the observation of self-focusing and defocusing of TEA CO₂-laser pulses in NH₃. Self-focusing of the 9R(30) CO₂ laser line resulted in a significant spatial narrowing of the laser beam after propagating through a 100 cm long cell containing NH₃ at a relatively low pressure of 1 Torr. Spatial broadening, characteristics of self-defocusing, has been observed for the 9R(16) CO₂-laser line.     

Energy transfer in slab dye lasers

A simple model of the energy transfer between a booster dye and the active dye in a flashlamp pumped planar waveguide dye laser is described.Analytical results are compared with experiments for several dyes in the 600–650 nm region.A twofold increase of laser output was found at a wavelength (630 nm) which is of particular interest for several applications.     

Spectral purity of pulsed dye lasers

High-spectral purity of pulsed dye lasers is required by many experiments. Unfortunately, the dye laser output is usually accompanied by a spectrally broadband background of spontaneous emission (ASE). We have carried out detailed studies of the ASE background using a dye laser operating with an oscillator, pre- and main amplifier.Dedicated to Prof. Dr. Herbert Welling on the occasion of his 60th birthday