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The interaction of a very intense, very short laser pulse is modified by the presence of a preformed plasma prior to the main short pulse. The preformed plasma is created by a small prepulse interacting with the target prior to the main pulse. The prepulse has been monitored using a water-cell-protected fast photodiode allowing on every shot a high dynamic measurement of the pulse profile. Simultaneously we have used time-resolved interferometry to look at the preformed plasma on a 300 TW, 700 fs laser. The two-dimensional density maps obtained have been compared with two-dimensional hydrodynamic simulations.

Projection imaging of 0.1-microm lines and spaces is demonstrated with a Mo/Si multilayer coated Schwarzschild objective and 14-nm illumination from a laser plasma source. This structure has been etched into a silicon wafer by using a trilevel resist and reactive ion etching. Low-contrast modulation at 0.05-microm lines and spaces is observed in polymethylmethacrylate.

We demonstrate nearly diffraction-limited printing of 0.2-microm features, using soft x rays of approximately 36-nm wavelength. An open-stencil transmission mask with minimum features of 4 microm was imaged by a twentyfold-reduction Schwarzschild-type objective onto silicon wafers coated with various e-beam resists. Implications for soft-x-ray projection lithography are discussed.

A tunable ArF* (193-nm) excimer source is described that produces over 125 mJ/pulse (peak) at 10 pulses/sec. This device has a spectral width of less than 2 cm(-1) and a demonstrated tunability of nearly 320 cm(-1) from 192.8 to 193.9 nm. Tunability, bandwidth, and mode control are achieved by injecting the fourth anti-Stokes line (in H(2)) of a frequency-doubled dye laser into an ArF* excimer-amplifier system.

Coherent radiation at several wavelengths in the vacuum ultraviolet (VUV) has been generated by four-wave parametric oscillation in mercury vapor. When a powerful ultraviolet pump laser of frequency omega(p) is tuned to a two-photon resonance, VUV signal photons at frequency omega(s), as well as idler photons at frequency omega(i), are generated such that omega(s) + omega(i) = 2omega(p). A frequency-doubled dye laser tuned to two-photon resonance with the 6s6d(1)D(2) level near 280.3 nm produced output at 184.9 and 143.5 nm. A tunable krypton fluoride excimer laser tuned to two-photon resonance with the 6s10s (1)S(0) level near 248.7 nm produced output at 140.1, 130.7, 130.1, 125.9, and 125.0 nm. Approximately 1-microJ, 200-W pulses were observed at 143.5 and 125.9 nm.

A simple technique is described for the efficient detection of multiphoton transitions from metastable states of atomic or molecular species to their excited states of either even or odd parity. This technique is demonstrated in metastable He, and first measurements of n3S-n3D splittings for n = 18-22 are reported.

Tunable coherent radiation was produced at 35.5 nm by seventh-harmonic conversion of 248-nm radiation from a krypton fluoride excimer laser. The nonlinear interaction took place at the intersection of the laser focus and a pulsed, supersonic helium gas jet. Third- and fifth-harmonic generation produced coherent outputs at 83 and 50 nm in both helium and xenon gas jets.

We have observed the effects of magnetic fields on four-wave mixing processes in atomic vapors. We have studied coherent vacuum-ultraviolet generation in Sr vapor via the process omega(1) + omega(2) + omega(3) ? omega(4) in fields of up to 50 kG. Magnetic tuning of the resonances of the third-order nonlinear susceptibility X((3)) was used to modify the dependence of the sum-frequency output power on the generated wavelength.

Extreme ultraviolet (XUV) radiation from 100 to less than 30 nm is emitted from a laser-induced plasma generated on a liquid-mercury surface. This surface does not degrade even after tens of thousands of laser pulses. The 532-nm laser light focused on the mercury forms a bright plasma core and a plume extending several millimeters above the liquid level. The plasma core produces primarily continuum radiation, whereas the plume emits lines at wavelengths above 77 nm. The mercury plasma was generated at the entrance port of a normal incidence vacuum monochromator, and the dispersed XUV radiation was monitored with a photomultiplier tube.

A synchronously pumped dye laser is constructed that uses an actively mode-locked Q-switched Nd:YAG laser as the pump source. The system consists of a grating-tuned dye oscillator and two transversely pumped and one longitudinally pumped amplifier stages. Output energies of 1.5 mJ in a 20-psec pulse at 5700 A, corresponding to a peak power of 10(8) W, are obtained by using rhodamine 6G. The energy can be increased to 3 mJ at 25 psec FWHM. Characteristics of the amplification process employing short (50-psec) pump pulses are discussed.