Strong Picosecond Research Articles

Observation of multiple-harmonic radiation induced from a gold surface by picosecond neodymium-doped yttrium aluminum garnet laser pulses.

Illuminating a gold surface by strong (5 GW/${\mathrm{cm}}^{2}$) picosecond neodymium-doped yttrium aluminum garnet laser pulses at grazing incidence, we observed a generation of coherent beams of both even and odd harmonics up to fifth order in the reflected direction with efficiencies ${10}^{\mathrm{\ensuremath{-}}10--}$${10}^{\mathrm{\ensuremath{-}}13}$. The observed decrease of the harmonic efficiencies with increasing harmonic order is much weaker than predicted by perturbative theories.

Energy spectrum of photoelectrons produced by picosecond laser-induced surface multiphoton photoeffect.

Photoelectrons were produced from a gold surface using strong picosecond Nd:glass laser pulses of ${10}^{10}$-W/${\mathrm{cm}}^{2}$ intensity. Unexpectedly high (up to 600 eV) energies were observed in the electron energy spectrum only when space-charge effects were completely eliminated. This result is compared with the well-known electron energy spectra of the multiphoton ionization of gases.

Polarization-rotation switch using picosecond pulses in GaAs

Photorefractive and free-carrier nonlinearities in GaAs transfer energy from a strong picosecond pump, which is linearly polarized at an arbitrary angle to a weak s-polarized probe, into a p-polarized beam propagating in the probe direction. By placing the GaAs between a crossed pair of high-quality polarizers that are set to extinguish the probe in the absence of the pump, an efficient, high-contrast, high-speed optical switch is realized. By varying the pumpprobe ratio, delay, fluence, and polarization, we can maximize the intensity of the p-polarized component. This intensity with the pump present divided by that without the pump, the on-off ratio, is approximately 2 at fluences as low as 0.03 mJ/cm(2) and approaches 10,000 at fluences of 15 mJ/cm(2) and pump polarizations of 45 degrees .

DEPENDENCY OF APPARENT RELATIVE QUANTUM YIELD OF ISORHODOPSIN TO RHODOPSIN ON THE PHOTON DENSITY OF PICOSECOND LASER PULSE

Abstract— The quantum yield of bleaching of isorhodopsin relative to that of rhodopsin was measured by irradiation of both pigments with a steady light source or a picosecond laser pulse. The each pigment was prepared by incubation of 11‐cis or 9‐cis retinal with opsin, respectively. The ratio of isorhodopsin to rhodopsin in the quantum yield was estimated to be 0.37 using irradiation with a steady light, while with a weak picosecond laser pulse (excitation photon density: below 20 μ.J/1.8 mmφ), it was estimated to be 0.39. Both values are in good agreement with each other. On the other hand, excitation with a strong picosecond laser pulse (above 20 μ.J/1.8 mmφ) produced a larger ratio than 0.39, indicating that saturation effects can be easily observed by irradiation with strong picosecond laser pulses.

Cars probing of the Si Raman mode transformation during strong picosecond pulsed-laser irradiation

We report on picosecond coherent anti-Stokes Raman scattering ( CARS) probing of the Si optical phonon spectrum transformation during picosecond pulsed-laser irradiation. CARS spectra were obtained in reflection at various laser fluences up to melting. The observed spectrum broadening is theoretically explaned in terms of phonon heating and laser-induced mechanical stress build-up on a time scale of 10ps.

Electron spectroscopy at thresholds in single and double multiphoton ionization of strontium

Spectroscopy of photoelectrons produced by strontium atoms irradiated by strong picosecond laser pulses reveals excited states of ${\mathrm{Sr}}^{+}$ and, for the first time, electrons from stepwise double ionization. Different threshold behaviors are observed for these transitions.

Plasma dynamics in GaAs under strong picosecond surface excitation

We have investigated the time-resolved luminescence of GaAs in air at room temperature, under strong picosecond surface excitation. The energy density was in the range 4–40 mJ cm 2 and the excitation wavelength λ ex ≅ 0.53 μ. The peak temperature reached by the generated electron-hole plasma at the end of the excitation pulse amounts to T M ≅ 720 K at an energy density of about 10 mJ cm 2 . Further increase of the power induces surface damage on the sample. The plasma relaxes its kinetic energy at a slow rate of the order of 10 10 eV s , supporting our previous calculations which concluded that electron-phonon interactions are strongly screened by intravalley free-carrier collisions at high plasma density, so that the plasma cooling slows down.

Study of light‐scattering changes induced in tRNA solutions by a strong optical field of picosecond pulses

AbstractChanges in the light‐scattering components (λ = 0.53 μm) induced by a strong picosecond optical field (λ = 1.06 μm) applied to macromolecular transfer ribonucleic acid (tRNA) solutions were studied. Two beams were polarized vertically, and the intensity of the vertical and horizontal components of the light (λ = 0.53 μm) scattered at an angle of 90° were measured. The electric field of the strong 30‐ps laser pulse was 5.0 × 103 esu cgs. The experimentally determined changes allowed for calculation of the mean third‐order optical polarizability c, and its anisotropy δc. The measurements were performed in three different solutions: salt free, with magnesium ions, and without magnesium ions. Changes in tRNA structure reflected in changes of nonlinear light scattering, third‐order optical polarizability, and its anisotropy were observed.