Abstract

Terahertz (THz) radiation characteristics have been investigated for voltage-biased photoswitching devices (PSDs) coupled with dipole antennas made on magnetoresistive ${\mathrm{Pr}}_{0.7}{\mathrm{Ca}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ thin films. Even under a fixed illumination of femtosecond laser pulses with a power of $14\mu \mathrm{J}∕{\mathrm{cm}}^2$, we find the high electric strength in PSDs made on ${\mathrm{Pr}}_{0.7}{\mathrm{Ca}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ thin films in the charge-ordered (CO) state at $10\mathrm{K}$. THz radiation linearly enhances with an increase of the biased electric field up to $400\mathrm{kV}∕\mathrm{cm}$ without any change of the waveform of the radiated THz pulse. On the other hand, the static time-averaged photoconductance is nearly constant below $200\mathrm{kV}∕\mathrm{cm}$ but deviates from it above $200\mathrm{kV}∕\mathrm{cm}$. Such behavior can be ascribed to an increase in the change of the fraction of photogenerated metallic patches within the CO insulating phase. Therefore our findings show that not only ${\mathrm{Pr}}_{0.7}{\mathrm{Ca}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ but also other manganites having a CO state above room temperature may act as efficient THz radiation sources.

© 2006 Optical Society of America

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