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Electro-optic measurement of standing waves in a GaAs coplanar waveguide
No full text[[abstract]]The authors have successfully measured, for the first time, standing waves in a GaAs coplanar waveguide at frequencies of 8.2107 and 12.310 GHz by using harmonic-mixing electro-optic probing. The technique is nondestructive and has greater potential in expanding the measuring frequency band to millimeter wave. The authors describe the principle of the technique, the experimental setup, and the measurement results[[fileno]]2010144010013[[department]]物理
Self-bending and Asymmetric Spatial Self-phase Modulation Effects in Nematic Liquid-Crystal Films
Get PDF[[abstract]]Laser-induced beam bending and the far-field asymmetric diffraction ring pattern due to the self-bending and asymmetric spatial self-phase modulation (SPM) effects in nematic liquid-crystal films are investigated. The measured far-field patterns are in good agreement with numerical calculations based on the diffraction theory, taking into account the two dimensionally of the problem, the nonlocal effect, and the wave-front curvature effect. The individual contributions of the aforementioned effects to the far-field pattern are analyzed for the first time. It is shown that the outermost diffraction peak of the far-field pattern is not the strongest one and that a large fraction of the transmitted intensity remains in the central region (within +/- 6 mrad of the beam axis). Merging of some of the diffraction peaks in this region should also occur. Although the transmitted beam does deflect, the deflection angle does not increase monotonically with the incident laser intensity, as is the case for a purely Kerr-like medium. In the experiments discussed here, higher-order effects are present. As an example, it is shown that equally pronounced third- and fifth-order nonlinear optical SPM effects are responsible for an observed five-ring asymmetric ring pattern[[fileno]]2010144010026[[department]]物理
Buildup of steady-state picosecond pulses in an actively mode-locked laser diode array
Get PDF[[abstract]]We have studied experimentally the temporal and spectral characteristics of an actively mode-locked laser-diode array in an external cavity as it evolves to the steady state. It is found that the buildup time to steady-state picosecond pulses takes less than 45 round trips. The number of clusters of the longitudinal-mode spectrum reduces during the evolution and finally approaches a steady-state spectral distribution with the pulse energy mainly distributed among a few clusters near the line center[[fileno]]2010144010033[[department]]物理
The Effect of Dye Concentration on Picosecond and Femtosecond CW Passively Mode-Locked Ti-Sapphire / DDI Laser
No full text[[abstract]]The role of the saturable absorber dye DDI in the cw passively mode-locked Ti:sapphire/DDI laser both with and without compensation prisms is investigated. This laser self-starts when the concentration of the dye is greater than almost-equal-to 2 X 10(-4) M for both picosecond and femtosecond pulses. With the prism pair, the laser generates Gaussian pulses 150 fs in duration. The corresponding spectrum is sech2 in shape with a FWHM of 8 nm. These parameters are independent of the DDI concentration. Without the prism pair, the laser generates picosecond pulses with the FWHM decreasing from 8 to 3 ps as the dye concentration is increased from 2.5 x 10(-4) to 1 X 10(-3) M. Concurrently the pulse shape changes from a Lorentzian to a nearly symmetric two-sided exponential shape. The picosecond spectra for different dye concentrations are also presented[[fileno]]2010144010050[[department]]物理
Completely Self-starting Picosecond and Femtosecond Kerr-lens Mode-locked Ti:sapphire Laser
Get PDF[[abstract]]Completely self-starting and stable operation of a Kerr-lens mode-locked Ti:sapphire laser was realized in both picosecond and femtosecond regimes. The cavity has a symmetric X configuration with soft aperturing. Enhanced Kerr nonlinearity and reduced backscattering effects were thought to be key to obtaining stable self-starting self-mode-locked operation from 765 to 815 nm far the picosecond regime and from 770 to 835 nm for the femtosecond regime. The mode-locking starting time as measured by the onset of the second-harmonic signal ranged from 300 ms to 2 s, depending on cavity alignment. Preliminary data also suggest that intracavity intensity fluctuation necessary for the laser to evolve into stable mode locking could be as short as 10-40 ps[[fileno]]2010144010063[[department]]物理
Two-wavelength Interferometer based on a Two-color Laser-diode Array and the Second-order Correlation Technique
Get PDF[[abstract]]A novel two-wavelength interferometer is demonstrated that uses a tunable two-color laser-diode array as the light source. The synthetic wavelength can be easily tuned from 2 to 0.043 mm by variation of the spectral separation between the two wavelengths of the laser output. By using the second-order correlation technique we can directly retrieve the phase change at the synthetic wavelength with no need for sophisticated electronic signal processing[[fileno]]2010144010064[[department]]物理
Subpicosecond carrier lifetimes in arsenic-ion-implanted GaAs
No full text[[abstract]]We have investigated photoexcited carrier lifetimes in arsenic-ion-implanted semi-insulating GaAs by time-resolved reflectivity measurements. Subpicosecond carrier lifetimes (220 to 550 fs) which do not exhibit apparent dosage dependence for samples bombarded with 200 keV arsenic ions at increasing dosages in the range of 10(12) and 10(16) ions/cm(2) are reported. The shortest carrier lifetime was observed for the sample irradiated at 10(13) ions/cm(-2). These are the shortest lifetimes ever observed for ion-damaged GaAs and comparable to those of low-temperature molecular beam epitaxially grown GaAs, which is also nonstoichiometric with excess-arsenic-related, deep-level defects[[fileno]]2010144010068[[department]]物理
Effect of rapid thermal annealing on carrier lifetimes of arsenic-ion-implanted GaAs
No full text[[abstract]]Femtosecond time-resolved reflectivity measurements, structural, and electrical analyses have been performed to investigate the effect of rapid thermal annealing (RTA) on GaAs implanted with 200 keV arsenic ions at 1016 ions/cm2. Ultrashort carrier lifetimes from 0.48 fs to 2.3 ps were observed for samples annealed at temperatures between 600 and 800°C. The time constants are somewhat shorter than those of RTA-annealed low-temperature molecular-beam epitaxy grown material, while following the same trend of longer time constants and recovery of resistance at higher annealing temperatures. Arsenic precipitates were not observed[[fileno]]2010144010071[[department]]物理
Tunable Semiconductor laser with A liquid Crystal Pixel Mirror In a Grating-loaded external Cavity
No full text[[abstract]]The wavelength of a commercial red pointer laser diode has been tuned over 4nm digitally in 0.2nm steps with a folded telescopic gating loaded external cavity incorporating a liquid crystal pixel mirror. The sidemode-suppression ratio of the laser was better than 20dB throughout this range.[[fileno]]2010144010085[[department]]物理
THz-radiation emission properties of multi-energy arsenic-ion-implanted GaAs and semi-insulating GaAs based photoconductive antennas
No full text[[abstract]]The performance of THz photoconductive (PC) emitter antennas fabricated on multienergy arsenic ion implanted GaAs and semi-insulating GaAs was compared. High damage threshold biasing and large saturation optical-pumping power for multi-GaAs:As+ based PC antennas were reported. The carrier mobility in the As ion implanted layer of GaAs:As+ was found to be about 150 cm2/V/s, which was comparable to that of low temperature GaAs[[fileno]]2010144010096[[department]]物理