P. J. Wisoff

Characterization of an ultrahigh peak power XeF(C to A) excimer laser system

The gain characteristics of an electron-beam pumped XeF(C to A) excimer amplifier operating in the blue-green spectral region were investigated for several laser pulse lengths. Saturation energy densities of 50 and 80 mJ/cm/sup 2/ were measured for injected laser pulse durations of 250 fs and approximately 100 ps, respectively. A gain bandwidth of 60 nm was observed with approximately 100-ps pulse injection. Using an optimized unstable resonator design, the laser amplifier has produced 275-mJ pulses with a pulse duration of 250 fs and a 2.5 times diffraction-limited beam quality, making the XeF(C to A) amplifier the first compact laser system in the visible spectral region to reach peak powers at the terawatt level. >

Emission from ionic cesium fluoride excimers excited by a laser-produced plasma

CsF vapor generated in a heat pipe was excited by a laser-produced plasma. Temporally integrated spectra and time-resolved fluorescence on the ionic excimer transition Cs(2+)F(-) ? Cs(+)F were observed at 185 nm. The pressure dependence of the fluorescence is influenced by self-absorption in the CsF vapor. The fluorescence is assigned to the Cs(2+)F(-) ((2)Sigma(1/2), B)? Cs(+)F ((2)Sigma(1/2),X) transition.

Electron beam excitation of rare‐gas alkali ionic excimers

The observation of fluorescence from ionic rare‐gas alkali molecules excited by an electron beam is reported. Gas mixtures of argon and xenon with hot vapors of either rubidium or cesium were excited to obtain emission from (XeRb)+ at 164 nm and (XeCs)+ at 160 nm. The spectral features observed in (XeRb)+ are assigned to three upper electronic states.

Absorption spectra of alkali halide molecules in the vacuum ultraviolet

The ultraviolet (UV) and vacuum ultraviolet (VUV) absorption spectra of three alkali halide molecules CsF, CsCl, and RbF have been determined experimentally. The longest wavelength absorption features are attributed to bound–free or bound–weakly bound transitions where the upper state correlates to ground state alkali and halogen atoms. The absorption at shorter wavelengths is due to transitions from the bound ground state to excited states that correlate to excited alkali and neutral halogen atoms. The covalent repulsive curves of CsF were found to have a close resemblance to the curve corresponding to the first ionization potential of CsF. The peak absorption cross sections are similar for the CsF and RbF molecules. CsCl molecules have a three to four times larger absorption cross section for the analogous upper states. The absorption oscillator strengths have been determined from the measured absorption cross sections, and are compared to those of other alkali halide molecules that have UV absorptions.

Analysis of lens and zone plate combinations for achromatic focusing of ultrashort laser pulses

Analysis of a combination zone plate and lens system is presented for the design of optical systems to focus ultrashort laser pulses. A system design that is free of propagation-time delay distortion and chromatic aberration is presented.

Ultrashort-laser-pulse amplification in a XeF[C --> A] excimer amplifier.

Tunable blue-green subpicosecond laser pulses have been amplified in an electron-beam-pumped XeF(C --> A) excimer amplifier. Small-signal gains of 3.5% cm(-1) were measured using a 50-cm active gain length. At output energy densities as high as 170 mJ/cm(2), only a small degree of saturation occurred, resulting in a gain of 2.5% cm(-1).

Characterization of plasmas from a pulsed jet discharge for applications VUV spectroscopy and micromechanics

Plasmas from a pulsed jet discharge have been characterized with respect to gas species and nozzle design. Spectral lines from the gas used in the pulsed nozzle are apparent in the visible region. The vacuum ultraviolet spectrum, particularly for heavier gases, is dominated by emission from species sputtered from the nozzle. The production of highly ionized and excited states from materials created by the sputtering of the nozzle has possible applications in VUV (vacuum ultraviolet) spectroscopy. Operating the pulsed jet discharge at a 50-Hz repetition rate with NF/sub 3/ to produce excited fluorine ions allowed etch rates in excess of 10 mu m/min to be achieved in silicon; this may have applications to micromechanics. >

Tunable, high-power, subpicosecond blue-green dye laser system with a two-stage dye amplifier

A two-stage dye amplifier design has been developed to amplify tunable, blue-green, subpicosecond dye laser pulses which are generated from a hybrid synchronously mode-locked dye oscillator directly (800 fs) or shorter to 200 fs by a fiber compressor stage. This system has achieved single pulse energies of 2 mJ, with an amplified spontaneous emission content of less than 0.1%. Using 40 mJ of the third-harmonic output of an Nd:YAG regenerative amplifier to pump the dye amplifier system, these pulse energies represent an energy extraction efficiency of approximately 5%. The tunability, stability, and spatial and temporal quality of the output pulses from the system have also been characterized. >

Quantitative time‐resolved observations of ground‐state zinc atoms, methyl radicals, and excited CH radicals resulting from the 193 nm photodissociation of dimethylzinc

The ArF laser photodissociation dynamics of dimethylzinc at 193 nm have been studied, and their implications for the growth of ZnSe thin films are discussed. A broadband, vacuum ultraviolet argon plasma emission has been used to acquire time‐resolved absorption profiles from ground‐state Zn atoms and methyl radicals. Time‐resolved fluorescence from excited CH radicals has also been studied. The results indicate that the Zn concentration remains constant from 100 ns to 2 ms after the dissociating ArF pulse, indicating that this system is a good source for free Zn atoms. The CH3 radicals are formed immediately after the dissociation pulse and recombine within several hundred microseconds to form ethane. There was no indication of monomethylzinc (MMZn) formation, and the detected CH radical is likely to combine with H2 to form CH3 within several microseconds. This implies that the major sources for carbon contamination in the growth process (CH3, MMZn, CH) are unlikely to reach the growth surface.

Excimer Lasers In Medicine

Excimer lasers emit light energy, short optical pulses at ultraviolet wavelengths, that results in a unique laser tissue interaction. This has led to an increasing number of studies into medical applications of these lasers in fields such as ophthalmology, urology, cardiology and neurology.