| Research Abstract |
Firstly, using the equipment for the terahertz pulse generation and waveform measurement setup based on the EO sampling, both have been constructed by the end of last year, focusing and free-space propagation of terahertz pulses were studied. This is necessary to achieve high electric field with the waveform of the pulses under control. Secondly, new optical setup using off-axis parabolic mirrors with a shorter focal length was newly made, and focusing properties of terahertz pulses were studies. From these studies, the following has been clarified : i) The negative trailing part of the pulse, which has been observed by many groups including us, was found to be caused by the cutoff of the waveguide effects of metal structures constituting the EO crystal holder. ii) By knife-edge measurements at the focal plane, frequency-dependent focusing properties has been clarified, which has been shown to be in good agreement with the results of the Gaussian beam theory. iii) Maximum field of 11 kV/cm has been achieved, which is, to our knowledge, is the world record of the values directly measured by the EO method.
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