Fiber-based pulse stretcher for narrowband terahertz pulse generation with a chirped-pulse beating method

Abstract

We theoretically show that it is possible to generate chirp-free terahertz (THz) pulses with a chirped-pulse beating method by using an optical fiber as a pulse stretcher. Proper choices of the core radius and the dopant fraction of the core material of a step-index single-mode optical fiber eliminate the third-order spectral phase of the fiber, thus giving the pump laser pulse a purely linear chirp. We also show that even a standard commercial single-mode optical fiber can give THz pulses of lower chirp than the lower limit for a grating pair. We perform experiments to verify our theory.

The chirp-control of frequency-tunable narrowband terahertz pulses by nonlinearly chirped laser pulse beating

“…21,22 Figure 1 shows the schematic of the chirped-pulse beating. We begin by using a transform-limited Gaussian input laser pulse with a center frequency x 0 and a pulse width r, whose electric field is given by…”

“…Our method is based on the frequency-tunable narrowband THz pulse generation by photomixing with chirped laser pulse pairs (the so-called chirped-pulse beating). 19,20 By using the direct relationship between the spectral phase of the pulse stretcher and the chirp of the generated THz pulse, 21,22 and by changing the incident angle of the grating-based laser pulse stretcher, we can control the frequency sweep rate of the linear chirp of the THz pulse. This method is not only applicable in photomixing in a photoconductive antenna, but also it can be applied to various other THz pulse generation mechanisms.…”