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12 November 1999 1.55-μm two-photon absorption generation of subpicosecond electrical pulses in LT-GaAs photoconductors
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Subpicosecond electrical pulses have been generated from low temperature grown GaAs (LT-GaAs) coplanar stripline photoconductive switches by illumination of 160 fs optical pulses at 1.55 micrometers , which corresponds to below bandgap radiation. The device optical response was attributed to two photon absorption (TPA) as confirmed by the observed quadratic dependence of the DC photocurrent on average incident illumination. At a bias of 39 V and 5.16 mW average illumination a 2.6 (mu) A photocurrent was measured which corresponded to a 0.5 mA/W switch responsivity. For similar switch geometries fabricated onto LT-GaAs and illuminated by above bandgap radiation, responsivities of a few mA/W have been measured. Therefore TPA switch triggering has retained acceptable responsivity levels. The contribution of TPA to the device photoresponse was also confirmed by the dependence of the photocurrent on incident polarization direction; the TPA coefficient exhibited a strong anisotropy with respect to polarization. The device generated electrical pulses (impulse photoresponse) were measured using double sliding-contact photoconductive sampling techniques. Impulse photoresponses with full widths at half maximum of 451 fs were observed which are, to date, the fastest responses measured from LT-GaAs switches at this wavelength. Fourier transformation of the time domain data revealed electrical transients with 3 dB bandwidths of 190 GHz. The feasibility of back illumination of these devices at 1.55 micrometers was also demonstrated. Based on these highly encouraging results freely positionable photoconductive switches were fabricated and at present they are being tested.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Hernan Erlig, Shamino Wang, Talal Azfar, Anand Udupa, Harold R. Fetterman, and Dwight C. Streit "1.55-μm two-photon absorption generation of subpicosecond electrical pulses in LT-GaAs photoconductors", Proc. SPIE 3795, Terahertz and Gigahertz Photonics, (12 November 1999);


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