Modified THz electro-optic sampling for high optical modulation depth, large dynamical range, and low background noises.

Abstract

We present a modified THz electro-optic sampling method to combine the advantages of its two traditional counterparts at near 0° and 45° optical biases: excellent ability to cancel the background noises, high optical modulation, and large dynamical range. The first advantage results from the method's symmetrical layout to get dynamical noise cancellation. By setting the static birefringent phases of the two balanced beams with a pair of opposite numbers, our setup can record THz waveforms without distortion with its maximal modulation depth, thus optimal signal-to-noise ratio (SNR). The setting also releases the linearity of the measured signal from the static birefringence, thus enlarging greatly the linear dynamical range. For a given THz field, the recorded SNR with our setup, without a lock-in, is more than 10 times higher than that with the "crossed and balanced" design [IEEE Trans. Microwave Theory Tech. 47, 2644 (1999)].