Few-cycle terahertz generation and spectroscopy of nanostructures.
We report on new schemes for terahertz (THz) generation. The THz efficiency of photoconducting antennas can be increased by using a cavity effect for the near-infrared pump beam. The cavity is formed by a molecular beam epitaxy grown semiconductor Bragg mirror below the photoconducting layer. The optical confinement is accompanied by an electrical confinement suppressing undesired leakage currents and providing a constant electric field in the active layers. The performance of this cavity-enhanced emitter is further improved by using a mobility optimized low-temperature GaAs layer. This emitter is successfully used in a femtosecond Ti:sapphire laser cavity for highly efficient intracavity THz generation, where the photoconductive layer serves also as a saturable absorber. The broadband THz pulses generated are used for time-resolved spectroscopy of nanostructures. We study the dynamics of intersubband transitions in semiconductor quantum wells. The relaxation of carriers excited by a near-infrared pump pulse is investigated by measuring the THz absorption between the different subbands with our THz pulses. For transition energies below the optical phonon energy we find relatively long relaxation times with a strong dependence on the excited carrier density.
Institute of Solid-State Electronics, Vienna University of Technology, Floragasse 7, 1040 Vienna, Austria.
Juraj
J
Darmo
Thomas
T
Müller
Wolfgang
W
Parz
Josef
J
Kröll
Gottfried
G
Strasser
Karl
K
Unterrainer
D001152:Arsenicals / Q000032:analysis / Q000737:chemistry* / Q000528:radiation effects; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005708:Gallium / Q000032:analysis / Q000737:chemistry* / Q000528:radiation effects; D008872:Microwaves; D036103:Nanotechnology / Q000295:instrumentation* / Q000379:methods; D043942:Nanotubes / Q000032:analysis / Q000737:chemistry* / Q000648:ultrastructure*; D015203:Reproducibility of Results; D012666:Semiconductors; D012680:Sensitivity and Specificity; D013055:Spectrophotometry, Infrared / Q000295:instrumentation* / Q000379:methods
D001152:Arsenicals; C043055:gallium arsenide; D005708:Gallium