On the Chirp of Narrowband Terahertz Pulses Generated by Photomixing with Nonlinearly Chirped Laser Pulse Pairs

Abstract

The spectral linewidth and intensity of narrowband terahertz pulses generated by photomixing with beating of nonlinearly chirped laser pulse pairs are studied. The direct relationship between the dispersion of the pump pulse stretcher and the chirp of the terahertz pulse is shown. Simple analytical expressions for the linewidth and intensity of the terahertz spectrum are obtained and their validity is confirmed by numerical simulations. Generation of narrowband terahertz pulses with minimal chirp is demonstrated.

Laser-induced magnetization curve

“…Our proposal is to change Ω from a small value to a larger value as slowly as possible. In other words, an upchirped THz laser pulse is required [13,27]. In this paper, starting from the zero field ground state (GS), we show that the system under a upchirped laser almost follows the GS in static magnetic field up to full magnetization in time evolution of the wave function.…”

Suppressing Chirp of THz Pulses by Using an Optical Fiber as a Pulse Stretcher for Chirped Pulse Beating

“…A grating pair is typically used as a pulse stretcher for chirping the laser pulses. In our previous study [2], we derived the direct relationship between the dispersion of the pulse stretcher and the chirp of the THz pulse and demonstrated suppressing the chirp of THz pulses by using a grating pair as a pulse stretcher. However, there is a fundamental lower limit of the chirp of the THz pulses when a grating pair is used as a pulse stretcher.…”

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.…”

“…Except for the parameters of the grating-pair pulse stretchers, the setup is the same as seen in our earlier work. 21 Specifically, we use a pulsed fiber laser with an approximately Gaussian intensity spectrum with a center wavelength k 0 ¼ 805 nm and FWHM of 9.2 nm, a temporal full-width at half-maximum intensity of 130 fs, and an average output power of 10 mW, for the laser source. We use grating-pair pulse stretchers in a standard double-pass configuration with a fixed grating constant of d À1 ¼ 1200 lines/mm and four incident angles c ¼ 0 , 1 , 4 , and 10 ; where the perpendicular separations are, respectively, chosen to be b ¼ 1, 2, 5, and 11 cm to assure that the values of U (2) are almost constant, thus stretching the laser pulses to almost the same pulse width of about 45 ps.…”