Measurements Of Temporal Behavior Research Articles

Generation of coherent off-diagonal raman-active phonons by femtosecond laser pulses in high-temperature superconductor YBa2Cu3O7−x

The time-resolved optical response from various crystallographic planes of a YBa2Cu3O7−x monocrystal is investigated. In such measurements of temporal behavior, the phonon system is driven by an ultrashort (subpicosecond) pulse into a coherent state and is probed by a second ultrashort pulse with a given temporal delay. A comparison of the Fourier transforms of the temporal responses with the spontaneous Raman scattering spectra shows that the contribution to a temporal response comes not only from fully symmetric phonons, but also from off-diagonal modes. The mechanism of generation of coherent phonons in high-temperature superconductors is discussed.

Measurement of temporal behavior of electron density in a discharge-pumped ArF excimer laser

Time-resolved number densities of electrons in a discharge-pumped ArF excimer laser are measured by an interferometric method. The peak electron density is 6.7/spl times/10/sup 15/ cm/sup -3/ at a total gas pressure of 2.5 atom, a gas mixture ratio of F/sub 2/-Ar-He=0.2-10.0-89.8, and a charging voltage of 24 kV for a 68-nF storage capacitor bank. The dependences of the electron density and laser output power on the Ar and F/sub 2/ fractions in Ar-F/sub 2/-He mixture and on the Ne-He mixing ratio in Ar-F/sub 2/-He-Ne mixture are investigated, and the effects of Ar-F/sub 2/-He-Ne mixing ratio on the ArF laser discharge are discussed. The experimental data of the peak electron density are also compared with the results of a computer simulation. A good agreement between them was obtained by considering the fact that the actual discharge volume occupied only part of the electrode width.