Group theory and experiments on helical and linear distributed feedback gas lasers

This study puts forward the concept of helical distributed feedback (DFB) lasers. The basic features of this new type of laser are derived by group theoretical considerations on cylindrical, circular linear periodic, and helical waveguide and laser structures. It is demonstrated that not only linear periodic structures but also helical structures show Bragg and DFB effects. Microwave and far-infrared experiments on passive helical metal waveguides reveal Bragg resonances in transmission. These results initiated the first experimental realization of a helical DFB gas laser, i.e. an optically pumped 496m CH₃F laser with a helical metal waveguide of a pitch close to 250m. This helical DFB laser shows higher-mode selectivity than the corresponding linear DFB laser. Finally, we show that the concept of helical DFB also applies to dye lasers with internal DFB incorporated by a mixture of the dye with a cholesteric liquid crystal.On leave from the Polish Academy of Sciences, Gdansk, Poland     

Dynamics of lasers with two-dimensional distributed feedback

A model of a laser exploiting two-dimensional (2D) distributed feedback is developed. A new feedback mechanism can be realized using a dielectric structure with the width having double-periodical sinusoidal or chessboard modulation. It is shown that 2D Bragg resonator possesses high selectivity over both the longitudinal and the transverse indices. Within semi-classical approach nonlinear dynamics of 2D distributed feedback laser (DFL) is studied and spatial synchronization of radiation from extended active medium is demonstrated.     

Ultrashort pulse generation by distributed feedback dye lasers. II

The properties of distributed feedback dye lasers as novel sources for wavelength tunable ultrashort pulses in the visible and ultraviolet range are studied. Calculated and measured energy characteristics of the laser are in very good agreement. The shot-to-shot stability of the single ultrashort pulses has been measured to be ±7.1%.     

Ultrashort pulse generation by distributed feedback dye lasers. I

The N₂-laser pumped distributed feedback dye laser is a new type of picosecond light source. A rate equation model describing the ultrashort pulse formation is presented. The temporal behavior of the distributed feedback dye laser predicted by the model has been compared with experimental results obtained with a streak camera system. The observed good agreement allows application of the theoretical model for the engineering of an inexpensive picosecond laser     

Energy theory of waveguide distributed feedback gas lasers

In this paper systematic numerical studies of the nonlinear operation of a waveguide distributed feedback gas laser equipped with a metal waveguide of rectangular cross section are presented. An approximate formula relating small-signal gain with the output power and the parameters of the structure for this kind of lasers is derived. Characteristics revealing saturation effects for weak as well as strong coupling regions are presented.Academic guest from the Institute of Microelectronics and Optoelectronics, Technical University, Warsaw, Poland     

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.     

Subpicosecond,widely tunable distributed feedback dye laser

A simple, achromatic, widely tunable distributed feedback dye laser arrangement is described. It makes use of a microscope objective, which images a transmission grating into the active medium. With this arrangement subpicosecond operation and broad tunability (400–760 nm) is reported.     

Pulse generation by distributed feedback dye lasers

Equations describing the pulse generation by distributed feedback dye lasers are derived and solved by analytical methods. The dependence of the laser output on macroscopic parameters is discussed.On leave from the Department of Physics, Friedrich-Schiller-University, DDR-6900, Jena, German Democratic Republic     

Novel achromatic distributed feedback dye laser for subpicosecond operation

The optical pump arrangement of distributed feedback dye lasers (DFDLs) having a grating beam splitter is analyzed in detail. The upper limit of the pump spectral bandwidth and beam divergence are given as a function of the length of the excited volume. A novel achromatic pump arrangement is reported which is capable of producing a short, high visibility interference pattern even if a divergent pump source of several nm bandwidth is used. The DFDL pulse duration has an estimated lower limit of 200 fs.     

Spatially-hole-burned distributed feedback dye laser produced tunable single picosecond pulses

A new type of distributed feedback dye laser is described in which the Bragg grating is formed by spatial hole-burning. With a simple excimer laser pumped arrangement, single high stability 6 ps pulses were generated. The pulses were nearly transformlimited and were 33 times shorter than the rise time of the pulse which created the Bragg grating.on leave from JATE University, Department of Experimental Physics, Dóm tér 9, H-6720 Szeged, Hungary     

Generation of 320 fs pulses with a distributed feedback dye laser

A new achromatic distributed feedback dye laser (DFDL) arrangement is described. The experimental conditions for subpicosecond pulse generation with the new device were investigated. For the first time, stable generation of subpicosecond pulses (350 fs) at 616 nm was achieved with a DFDL. The simultaneous spectral and autocorrelation measurements showed that the amplified DFDL pulses are nearly transform limited, having a pulse form close to the sech² shape.     

A novel picosecond distributed feedback dye laser arrangement for excimer laser pumping

A distributed feedback dye laser arrangement is described which can generate pulses at the subharmonic wavelengths of the main excimer laser lines (308 nm, 248 nm, 193 nm, etc.). The laser can be pumped with broadband lasers, such as the XeCl^* laserpumped dye laser with competing cavities. The laser is designed to be used as a part of a femtosecond, terawatt excimer laser system.     

Laser modes in organic solid-state distributed feedback lasers

We report on the laser modes in optically pumped solid-state lasers using an electroluminescent organic semiconductor as the active medium. Mechanically flexible distributed-feedback lasers are fabricated by depositing a thin film of an active material onto a nano-patterned polyester substrate either via spin-coating of a soluble ladder-type poly(p-phenylene) or via vacuum co-sublimation of small organic molecules. The different surface texture resulting from the fabrication process causes different feedback mechanisms. In both lasers higher lateral modes give rise to a broadening of the laser spectra at higher pumping levels. Received: 7 August 2000 / Revised version: 12 September 2000 / Published online: 8 November 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.     

Frequency stabilization and transverse mode discrimination in injection-seeded unstable resonator TEA CO2 lasers

Longitudinal mode selection by injection has been demonstrated as a viable technique for TEA-CO₂ lasers with pulse energies of a Joule or greater. Once reliable generation of single-longitudinal-mode (SLM) pulses is obtained, one can study the characteristics and the causes of intrapulse frequency variation. These include the effect of the decaying plasma, the thermal gradient due to the energy dissipation associated with the laser mechanism itself, and the pressure shift of the center frequency of the laser transition. The use of the positive-branch unstable resonator as an efficient means of coupling a discharge with large spatial dimensions to an optical cavity mode introduces another concern: namely, what can be done to emphasize transverse mode discrimination in an unstable resonator cavity while maintaining high coupling efficiency. These issues are discussed in this paper, and relevant experimental results are included.     

20 ps pulse generation by an excimer laser pumped double self-Q-switched distributed feedback dye laser

The behaviour of an excimer-laser-pumped distributed feedback dye laser (ELP DFDL) using a mixture of saturable absorber and laser dye as an active medium was studied. In a DFDL self-Q-switching occurs because of the population inversion dependence of the feedback. If the DFDL contains absorber saturation of the absorption by the leading edge of the created laser pulse also causes Q-switching. As a result of this double self-Q-switching, mixing a saturable absorber into the laser dye, the laser pulses become shorter and more stable. This was demonstrated experimentally. Mixing Rhodamine B into the dye solution of a Coumarin 153 ELP DFDL, a six-fold reduction in the pulse duration and a more than two-fold reduction in the pulse energy instability were observed. The experimental results were in good qualitative agreement with the predictions of a simple rate equation model.     

Thermal lens and its effects in copper-vapor lasers

We have analyzed and measured the thermal lens of the copper-vapor laser by considering both its windows and active medium. The equivalent combined focal length varies with operation parameters and it is sensitive to the laser geometry. The results are verified by our measurements on a 20 W device with 35 mm internal diameter tube. The thermal lens effects on the beam properties are analyzed and verified with the experiments for both oscillator and laser chain case.     

A high-power subpicosecond distributed feedback dye laser system pumped by a mode-locked Nd: YAG laser

The design and operation characteristics of a distributed feedback dye laser (DFDL) system pumped by the second harmonic of a flashlamp pumped mode-locked Nd: YAG laser are described. The DFDL oscillator facilitates a large tuning range with nearly Fourier limited pulse durations of about 1.6 ps. The combined action of saturated absorption and amplification results in a pulse shortening to about 600 fs, with small fluctuations in the pulse duration. Output pulse energies of more than 400 J are achieved, corresponding to a peak power of more than 650 MW. Since the dye amplifiers are pumped by pulses of only 25 ps duration the amplified spontaneous emission (ASE) is very low, typically less than 10^–4.     

Efficient distributed feedback solid state dye laser with a dynamic grating

We present the first operation of a distributed feedback solid state dye laser with a dynamic, pump-induced grating. Broadly tunable, narrow band operation in the region of 616 nm (604–649 nm) has been demonstrated with perylene red laser dye doped in poly(methyl methacrylate) (PMMA), when pumped with a frequency doubled Nd:YAG laser. Conversion efficiencies of 20%, corresponding to 35% optical-to-optical efficiency, have been measured. The laser bandwidth was between 0.01 and 0.04 nm, and smooth tuning over more than 200 GHz has been demonstrated. Received: 29 March 1999 / Published online: 24 June 1999