Femtosecond transition‐state absorption spectroscopy of Bi atoms produced by photodissociation of gaseous Bi2 molecules

Predissociation of Bi2 A(0u+), v′=21–39

Collisionless lifetimes for Bi2 A(0u+), v'=20-39, J'<or=105 have been measured using pulsed laser induced fluorescence techniques to investigate the effects of predissociation. The observed predissociation rates, Gamma=kpd(v')J(J+1), are quite rapid, ranging from kpd=1.53x10(2) s-1 for v'=21 to 1.5x10(5) s-1 for v'=39. The dense Bi2(A-->X) spectrum required both traditional lifetime measurements and synthetic spectrum fits to laser excitation spectra to determine the full range of observed rates. A single, repulsive potential responsible for the observed A-state predissociation could not be identified to adequately describe the vibrational dependence of the predissociation rates.

Electromagnetic bubble generation by half-cycle pulses

Electromagnetic (EM) bubbles (EMB's), unipolar, super-short, and intense nonoscillating solitary pulses of EM radiation, can be generated in a gas of nonlinear atoms by available half-cycle pulses (HCP's). We investigate how EMB's characteristics (amplitude, length, formation distance, and total number) are controlled by the amplitude and length of originating HCP's. We also predict shocklike wave fronts in the multibubble regime.

Femtosecond vacuum-ultraviolet pulse measurement by field-ionization dynamics

Three techniques are demonstrated for measuring femtosecond pulses from the deep vacuum ultraviolet to the visible based on the ionization dynamics of optical-field-ionized plasmas. A probe pulse propagates through a plasma generated by an intense femtosecond KrF excimer laser pump pulse. Ionization-induced defocussing or collisional absorption yield a cross-correlation measurement of the probe pulse. Ionization-induced spectral blue shifting of the probe can give an upper limit for the probe pulse duration.

Ultraviolet ultrafast pump-probe laser based on a Ti:sapphire laser system

An ultrafast spectroscopic pump-probe apparatus for detection of ultraviolet time-resolved spectra is described. Frequency doubling of an 810-nm 0.3-TW Ti:sapphire laser system yields 15-mJ 165-fs pulses at 405 nm. We obtain pulse energies of 0.8 mJ by frequency tripling to 270 nm. An ultraviolet supercontinuum extending from 200 to 600 nm is also generated in water by use of the frequency-doubled 405-nm light. The system operates at a 5-Hz repetition rate and is useful for applications in deep-ultraviolet pump-probe subpicosecond spectroscopy.

Spectrally compensated sum-frequency mixing scheme for generation of broadband radiation at 193 nm

A dispersively compensated scheme for sum-frequency mixing of broadband ultrashort laser pulses is reported. An increase of the bandwidth of the sum-frequency mixing process by 12 times compared with the noncompensated bandwidth of the given crystal has been demonstrated. Mixing radiation at 266 and 707 nm in a 1-mm-thick beta-barium metaborate crystal by using the compensated scheme results in an output bandwidth of 0.6 nm at 193 nm, which corresponds to a minimum output pulse duration of 90 fs.