Generation of continuous-wave terahertz radiation using a two-mode titanium sapphire laser containing an intracavity Fabry–Perot etalon

Abstract

Continuous-wave terahertz ͑THz͒ radiation was generated by photomixing two modes of a titanium sapphire laser. The laser was induced to oscillate on two modes by placing a Fabry-Perot etalon in the laser resonator. The frequency of terahertz radiation, which was equal to the difference frequency of the two modes, was varied by adjusting the free spectral range ͑FSR͒ of the etalon. Photomixing was performed by logarithmic spiral antennas fabricated on low-temperature-grown GaAs; and the emitted THz radiation was characterized. The THz power, measured by a Golay cell, was 1 W at 0.3 THz and 0.7 W at 0.5 THz. The THz frequency, as determined by a Fourier transform interferometer, was seen to correspond to the etalon FSR. The current-voltage characteristics of photomixers were also determined, and photocurrent modulation was observed by the autocorrelation of the laser beam.

Autocorrelator for the measurement of a quasi-continuous-wave laser beam sinusoidally modulated at 17 THz

“…where s (1) and s (2) are the cross sections of one-and twophoton absorptions, respectively, P is the peak power of the laser, and z is the parameter, defined as z ¼ 2z/b, in which z is the distance from the beam waist to the photocathode surface, and b is the confocal parameter. The ratio of the signals arising from one-photon (first term) and two-photon (second term) processes can then be calculated using Eq.…”

“…A continuous-wave (CW) Raman laser arising from molecular hydrogen in a high-finesse cavity for generating a Stokes beam, the frequency of which is determined by a Raman shift frequency (587 cm À1 for the rotational transition and 4155 cm À1 for the vibrational transition) has recently been reported. Thus, it should generate a sinusoidal wave in the terahertz range [2]. In order to measure the beat signal, it is necessary to use an autocorrelator with a femtosecond resolution.…”

Review of laser‐diode pumped Ti:sapphire laser

“…As the output performance of LD‐pumped Ti:sapphire lasers is further improved, they may be widely used in optical transfection, 85 cellular microsurgery, 86 THz radiation generation, 87 spectroscopy, 88 coherent high‐harmonic EUV generation 89 and so on. In the near future, low‐cost and high‐performance LD‐pumped Ti:sapphire lasers will certainly blow a storm in many applications.…”

Terahertz Sources

“…A very short carrier lifetime (< 200 fs) is required for successful THz generation. The typical THz power generated is of the order of 1 mW [10] and the bandwidth is limited to approximately 1.5 THz. Owing to these limitations, such emitters have not found wide application.…”