J. Bohus

Resonant third harmonic generation of KrF laser in Ar gas.

Investigations of emission of harmonics from argon gas jet irradiated by 700 fs, 5 mJ pulses from a KrF laser are presented. Harmonics conversion was optimized by varying the experimental geometry and the nozzle size. For the collection of the harmonic radiation silicon and solar-blind diamond semiconductor detectors equipped with charge preamplifiers were applied. The possibility of using a single-crystal CVD diamond detector for separate measurement of the 3rd harmonic in the presence of a strong pumping radiation was explored. Our experiments show that the earlier suggested 0.7% conversion efficiency can really be obtained, but only in the case when phase matching is optimized with an elongated gas target length corresponding to the length of coherence.

Two-step preionization scheme for discharge pumped KrF excimer lasers

The beam homogeneity and stored energy of discharge pumped KrF excimer amplifiers are critically dependent on the preionization level of the active medium and on the rise time of the electric excitation pulse. Here a scheme is presented to increase the effectiveness of the preionization and to improve the rise time of the pump pulse by the use of the auto-spark-gap UV preionization of increased gap separation. The modified charging circuit has been proven to enhance the discharge quality and the amplification properties of the excimer module. The increased temporal jitter of the preionization sparks of large gap separation is eliminated by an additional pre-preionization scheme. The circuit is especially well suited for short-pulse KrF amplifiers.

Changes in DRIFT spectra of wood irradiated by lasers of different wavelength

An exact wavelength separation of the spectrum cannot be accomplished when utilizing common ultraviolet (UV) light sources, so the dependence of photodegradation on wavelength cannot be done directly. The photodegradation of wood resulted in by laser irradiation on various wavelengths can be studied by comparing the changes in the DRIFT spectra of various wood materials. The analysis of the difference spectrum is a widely used method to investigate the changes in the infrared spectrum. As this procedure cannot be used to compare the changes quantitatively, a new indicator was introduced, termed Band Damage Index (BDI). The BDI and the results obtained by its analysis are going to be discussed.

Differential pumping scheme for discharge pumped excimer lasers

The beam homogeneity and stored energy of discharge pumped excimer amplifiers are critically dependent on the prepulse level of the electric excitation pulse. Here a scheme is presented to decrease significantly the prepulse level by differential charging of the two electrodes. The modified charging circuit also enables to increase the amplitude and improve the rise time of the main pulse, thus improving the discharge quality and the amplification properties of the excimer module. The circuit is especially well suited for short-pulse KrF amplifiers.

Two-Photon-Absorption of BBO, CLBO, KDP and LTB Crystals

The two photon absorption coefficient of long BBO, CLBO, KDP and LBO samples was determined from the intensity dependent transmission in the range of 0.2 - 80 GW/cm2 using 650 fs laser pulses at 248nm.

An all-reflective polarization rotator

The conceptual design and proof of principle experimental results of a polarization rotator based on mirrors are presented. The device is suitable for any-angle, online rotation of the plane of polarization of high peak intensity ultrashort laser pulses. Controllable rotation of the polarization vector of short laser pulses with a broad bandwidth requires achromatic retarding plates which have a limited scalability and the substantial plate thickness can lead to pulse broadening and inaccurate polarization rotation. Polarization rotators based on reflective optical elements are preferable alternatives to wave plates especially when used in high average power or high peak intensity ultra-short laser systems. The control of the polarization state is desirable in many laser-matter interaction experiments e.g., high harmonic and attosecond pulse generation, electron, proton and ion acceleration, electron-positron pair creating, vacuum nonlinear polarization effect. The device can also serve as a beam attenuator, in combination with a linear polarizer.

Three-channel KrF laser with distributed magnetic-switch-based charging circuit

A novel magnetic-switch-controlled L−C inversion circuit is proposed for discharge pumped excimer lasers of three separate channels. The charging circuit is controlled by one thyratron and one common “distributed” magnetic switch. Stable synchronization of the channels and the capability for amplification or generation of three separate pulses of constant delay are unique features of this scheme.