Temperature dependence of femtosecond electromagnetic radiation from semiconductor surfaces

Abstract

We present observation of temperature dependence of optically induced femtosecond electromagnetic radiation from several semiconductors. When the sample temperature decreases from 280 to 80 K, over 4 times and 21 times increases of the radiated peak field and radiated energy have been found. A large shift of the frequency spectrum of the radiation was observed when the InSb sample temperature was tuned over this range.

Polarity reversal of terahertz waves radiated from semi-insulating InP surfaces induced by temperature

“…This temperature dependence is considerably different from that reported for other semiconductors. [1][2][3][4]16,17 According to previous reports, THz radiation intensity increases monotonically with decreasing temperature and this is explained by the increase of the electron mobility at low temperatures. However, our results at low-density excitation that the polarity reversal occurs at 140 K and the amplitude decreases with decreasing temperature from 300 K cannot be explained only by the effect of the electron mobility.…”

“…[1][2][3][4][5][6][7][8][9][10] Studies on the applications of THz waves such as THz time-domain spectroscopy ͑THz-TDS͒ and imaging have been actively conducted. [5][6][7][8] Recently, the ultrafast dressing process of the charged particles in GaAs was clarified by analyzing the THz wave forms.…”

“…1-4,16 -18 The shape change of THz wave forms with temperature for InSb has been reported by Hu et al and they proposed that it is due to the changes of the depletion width and complex conductivity with temperature. 2 For the case of optical rectification, polarity reversal of THz radiation with temperature has been reported for GaAs when the excitation laser energy is close to the band-gap energy. 4 This result is interpreted by the sign change of the second-order susceptibility for optical rectification due to the change of band-gap energy with temperature.…”

Coherent and incoherent terahertz beams measured from a terahertz photoconductive antenna

“…[1][2][3][4] Although there are different methods of producing a broadband terahertz beam for TDTS, the most popular one may be the photoconductive antenna. [5][6][7][8][9][10][11][12] Since its invention, many research groups have adopted the photoconductive antenna, because it generates relatively strong terahertz pulses. 5 However, despite its popularity, there has been little systematic effort to assess the beam properties and the power output of the terahertz beam produced by the antenna.…”

“…12 The photocurrent, which is in fact the plasma oscillation between the electrodes, is expected to increase linearly with the pump-laser beam power and the AC bias voltage applied to the antenna. The AC bias voltage modulates the plasma to enhance the plasma oscillation amplitude, which in turn increases the coherent photocurrent and hence the coherent terahertz-beam strength.…”