S. Szatmári

Simplified laser system for the generation of 60 fs pulses at 248 nm

Abstract A simplified hybrid excimer-dye laser system is described, capable of generating subpicosecond pulses at most of the excimer laser wavelengths. In this paper ≈ 60 fs pulse generation is reported at 248 nm, using the above system and additional pulse compression. The effect of the operational conditions of different parts of the system and of the compressor on the spectral and temporal characteristics of the output pulse is studied.

Hybrid dye-excimer laser system for the generation of 80 fs, 900 GW pulses at 248 nm.

Abstract We report the generation of 80 fs pulses at 248 nm using a hybrid dye-excimer laser system. These pulses are amplified in a wide-aperture amplifier to 900 GW peak power.

ABSORPTION OF SUBPICOSECOND ULTRAVIOLET-LASER PULSES IN HIGH-DENSITY PLASMA

The absorption of 250 fs KrF laser pulses incident on solid targets of aluminum, copper and gold has been measured for normal incidence as a function of laser intensity in the range of 1012–1014 W cm−2 and as a function of polarization and angle of incidence for the intensity range of 1014−2.5×1015 W cm−2. As the intensity increases from 1012 W cm−2 the reflectivity at normal incidence changes from the low-intensity mirror reflectivity value to values in the range of 0.5–0.61 at 1014 W cm−2. For this intensity maximum absorption of 63–80% has been observed for p-polarized radiation at angles of incidence in the range of 54°–57°, increasing with atomic number. The results are compared with the expected Fresnel reflectivity from a sharp vacuum-plasma interface with the refractive index given by the Drude model and also to numerical calculations of reflectivity for various scale length density profiles. Qualitative agreement is found with the Fresnel/Drude model and quantitative agreement is noticed with the numerical calculations of absorption on a steep density profile with normalized collision frequencies, v/ω, in the range of 0.13–0.15 at critical density and normalized density gradient scale lengths, L/λ0, in the range of 0.018–0.053 for a laser intensity of 1014 W cm−2.At 2.5×1015 W cm−2 a small amount of preplasma is present and maximum absorption of 64–76% has been observed for p-polarized radiation at angles of incidence in the range of 45°–50°.

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.

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.

Simple generation of high-power, picosecond, tunable excimer laser pulses

Abstract A single excimer laser (a modified commercial oscillation-amplifier combination) is used to pump a dye laser generating a single ps pulse at twice the excimer wavelength and to amplify the frequency-doubled pulse to high peak powers. With XeCl at 308 nm an output pulse energy of 10 mJ with

Bandwidth limited amplification of 220 fs pulses in XeCl

Abstract Transform limited pulses of 200–250 fs duration at 308 ns generated by a specially designed excimer laser pumped dye laser system have been amplified in a XeCl gain module. Simultaneous study of the spectrum and the temporal behaviour of the amplified UV pulses showed bandwidth limitation by the gain spectrum of XeCl. This effect is strongly dependent on the operational condition of the amplifier; in a single pass amplification scheme 0.5 mJ, 250 fs pulses, in a double pass arrangement 5 mJ, 220 fs pulses were obtained, with excellent reproducibility.

Comparative study of the gain dynamics of XeCl and KrF with subpicosecond resolution

We have studied the subpicosecond gain dynamics of XeCl and KrF with the following results for XeCl (KrF): saturation energy density 0.85 (2.0) mJ/cm2, small-signal-gain coefficient 0.12–0.15 (0.20–0.22) cm−1, gain recovery of 62% (25%) with a time constant of 52 (54) psec. A molecular reorientation time of ≈1 psec was observed in both excimers.

Intensity-dependent loss properties of window materials at 248 nm.

Transmission of fused silica, CaF(2), LiF, and MgF(2) is measured using 450-fsec, 248-nm pulses in the range 10-120 GW/cm(2). Different loss mechanisms such as scattering of transmitted radiation, color-center formation, and multiphoton absorption were studied separately. For fused silica a two-photon absorption mechanism is found, while for CaF(2), LiF, and MgF(2) three-photon absorption and absorption due to color-center formation are found as dominant absorption mechanisms.

Pulse front and pulse duration distortion in refractive optics, and its compensation

Abstract In this paper a theoretical and experimental study of pulse front distortion of lens systems and spatially dependent pulse broadening in lenses and in prisms are presented. Pulse front distortions up to 10 times the pulse duration are found experimentally. Suggestion are made for distortion-free optics and also for possible compensation.