Frequency-doubled Laser Light Research Articles

Quasi-phase-matched second harmonic generation of UV light using AlN waveguides

As an alternative to electrically injected diodes, UV light emission can be obtained via second harmonic generation (SHG). In weakly birefringent materials such as aluminum nitride (AlN), the phase matching of the driving and second harmonic waves can be achieved by the quasi-phase-matching (QPM) technique, where the polarity of the material is periodically changed commensurate with the coherence wavelength. QPM also allows the use of the highest nonlinear susceptibility, and therefore, higher conversion efficiencies are possible. In this work, the QPM SHG of UV light in AlN lateral polar structure-based waveguides is demonstrated. The peak intensity of the frequency doubled laser light was measured at 344 nm and 472 nm wavelengths, in agreement with dispersion-based theoretical predictions. These results confirm the potential of III-nitride-based lateral polar structures for quasi-phase-matched nonlinear optics and for frequency doubling media for UV light generation.

Fast electron beam measurements from relativistically intense, frequency-doubled laser–solid interactions

Experimental measurements of the fast electron beam created by the interaction of relativistically intense, frequency-doubled laser light with planar solid targets and its subsequent transport within the target are presented and compared with those of a similar experiment using the laser fundamental frequency. Using frequency-doubled laser light, the fast electron source size is significantly reduced, while evidence suggests the divergence angle may be reduced. Pyrometric measurements of the target rear surface temperature and the Cu Kα imager data indicate the laser to fast electron absorption fraction is reduced using frequency doubled laser light. Bremsstrahlung measurements indicate the fast electron temperature is 125 keV, while the laser energy absorbed into forward-going fast electrons was found to be 16 ± 4% for frequency doubled light at a mean laser intensity of 5 ± 3 × 1018 W cm−2.

Measuring fast electron spectra and laser absorption in relativistic laser-solid interactions using differential bremsstrahlung photon detectors

A photon detector suitable for the measurement of bremsstrahlung spectra generated in relativistically intense laser-solid interactions is described. The Monte Carlo techniques used to extract the fast electron spectrum and laser energy absorbed into forward-going fast electrons are detailed. A relativistically intense laser-solid experiment using frequency doubled laser light is used to demonstrate the effective operation of the detector. The experimental data were interpreted using the 3-spatial-dimension Monte Carlo code MCNPX [D. Pelowitz, MCNPX User's Manual Version 2.6.0, Los Alamos National Laboratory, 2008], and the fast electron temperature found to be 125 keV.

Harmonic generation from solid-vacuum interface irradiated at high laser intensities

Observations of harmonic generation from solid Al targets irradiated at intensities of 10 17 W/cm 2 using a tabletop Ti:sapphire terawatt laser system are reported. For irradiances with laser light at a wavelength of λ = 794nm (the fundamental frequency), harmonics up to the 7th, while for irradiances with frequency doubled laser light ( λ = 397) nm harmonics up to the 4th of the respective incident radiation were detected.

Hyperfine structure of the lower configurations in Y II by fast ion beam-laser spectroscopy

The hyperfine structure (hfs) of levels in the configurations 4d5s, 4d2 and 4d5p in Y II has been recorded using fast ion beam-laser spectroscopy. The levels in the 4d5s configuration were excited with frequency doubled laser light to levels in the 4d5p configuration, whereas the levels in the 4d2 configuration were excited by visible laser light. All hfs components could not be observed in the spectra, and therefore the magnetic dipole coupling constants A were evaluated in a parametrization of the peak separations in the framework of the effective operator theory.

Direct measurement of the N 2 + dissociation energy

The accuracy for the direct measurement of the dissociation energy of the N 2 + B2Σ u +-state was significantly improved by using frequency doubled laser light, which enables the authors to excite from lowerv″-levels and additionally to calibrate the fundamental laser wavelength with an iodine cell. The obtained value is:D8(N 2 + )=70248±6 cm−1.

Isotope shifts of Zn neutral atoms measured by two-photon Doppler-free laser-induced fluorescence spectroscopy

Two-photon Doppler-free laser-induced fluorescence spectroscopy has been used for the first time to measure isotope shifts between the three most abundant stable isotopes of zinc (64, 66 and 68). A high-resolution laser system, consisting of an argon ion-pumped cw ring dye laser, a three-stage pulsed amplifier chain, and a doubling crystal, was used to generate tunable uv radiation for the experiment. Gas-phase Zn atoms were generated by laser-ablating a ZnS crystal. The Doppler-free spectrum was produced for the two-photon allowed 4s 2 1 S 0 −4d 1 D 2 transition (λ = 160 nm) of Zn by reflecting the laser beam back on itself. The measured isotope shifts were 976 ± 39 MHz for 64 Zn− 66 Zn and 888 ± 24 MHz for 66 Zn− 68 Zn. The technique of producing counter-propagating light by back-reflecting the laser beam has been used in situ to determine both the zero velocity frequency of particles in Doppler-shifted velocity distribution experiments and to measure the bandwidth of frequency-doubled laser light.