Terahertz wave parameter source frequency selection and frequency tuning method and device thereof

Abstract

The invention provides a terahertz wave parameter source frequency selection and frequency tuning method and device. Two beams of mutually crossed pump light excite a transverse optical phonon mode ina nonlinear crystal with infrared activity and Raman activity at the same time, and stimulated polariton scattering (SPS) is generated, a phase matching relationship of the SPS is limited by using crossed pump, frequency selection of Stokes light and corresponding THz waves is realized, and through continuously changing a cross angle of two beams of pump light, continuous tuning of frequencies ofcoherent narrow-band Stokes light and THz waves is realized. One scheme for realizing crossed pump is as follows: pump light is grabbed into the side surface of the nonlinear crystal and is totally reflected, the incident pump light and reflected pump light form a crossed pump form, and the incident angle and the total reflection angle of the pump light to the side surface of the crystal are changed by rotating the nonlinear crystal, so that the change of the phase matching relationship is realized. The method and the device have the beneficial effects that an independent Stokes optical seedsource is not needed, the device can be used under the condition of sub ns laser pump, and have the advantages of being simple in structure, convenient to operate, low in economic cost, high in THz wave generation efficiency and the like.

Description

technical field [0001] The invention relates to the technical field of tunable laser sources, in particular to a method for frequency selection and frequency tuning of a terahertz wave parameter source and a device thereof. Background technique [0002] Terahertz (THz) waves refer to electromagnetic waves with a frequency range of 0.1-10 THz and a wavelength range of 30-3000 μm. THz waves are between infrared rays and microwaves, and have a series of special properties that are not available in many other wave bands, the most notable of which are the penetrability of non-polar molecules and the characteristics of fingerprint spectrum identification, resulting in the most important THz waves. Two applications: THz penetration imaging and THz spectrum measurement. THz waves have shown great scientific research value and application prospects in many basic and applied research fields such as biomedicine, non-destructive testing, environmental monitoring, security inspection, a...

AI Technical Summary

Problems solved by technology

[0008] Although the structure of TPO is simple and the efficiency is high, the frequency tuning needs to mechanically adjust the angle between the resonant cavity and the pump light. Even if the automatic control tuning method based on the optical scanning mirror is developed later, the tuning speed is still slow and the system is stable. Poor performance, wide THz wave linewidth, etc., the Stokes light (6) resonant cavity length in TPO is generally more than ten centimeters, and a certain pump pulse duration is required to make the Stokes light (6) oscillate back and forth in the resonant cavity to obtain Fully amplified, so TPO can only be applied to the case of longer pump pulses, such as a few nanoseconds, but not to sub-nanosecond pulsed laser pumping, ns laser pumping will bring about the inhibition of SBS on SPS, Restricting the generation efficiency of THz waves

[0009] is-TPG can realize THz wave output with narrow line width. Through the grating automatic angle matching and tuning method, only need to change the wavelength of the seed laser, the phase matching angle can be automatically adjusted to achieve THz wave agility, but is-TPG needs a tunable Narrow linewidth seed laser source, high economic cost, and low seed source power, requires a long interaction length to achieve effective Stokes light (6) amplification and high-power THz wave generation, is-TPG pump spot The size is generally small, and the non-collinear phase matching method affects the spatial coupling between pump light and Stokes light (6), which limits the effective gain length and restricts the further improvement of THz wave generation efficiency. Linear phase matching can solve the problem of spatial separation between pump light and Stokes light (6), but the frequency tuning of quasi-collinear phase matching is limited to a very narrow range, which severely limits the tuning range of THz waves

[0010] In addition, there is a problem of gain competition in both TPO and is-TPG, that is, the competition of the center frequency with high SPS gain and high spatial coupling efficiency to the high-frequency THz wave with low gain and low spatial coupling efficiency makes the THz wave at high frequency It is difficult to be tuned out, which seriously affects the tuning range of terahertz waves at high frequencies

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