Method for generating coherent terahertz pulse based on resonance four-wave mixing
A terahertz pulse, four-wave mixing technology, applied in the optical field, can solve the problems of inability to radiate, limit, construct and use high cost, and achieve the effect of high conversion efficiency
Pending Publication Date: 2022-01-18
FUDAN UNIV
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Problems solved by technology
The second-order nonlinear crystal is limited by the absorption of the crystal itself, and cannot efficiently generate radiation in the 5-15THz band
Free electron laser is a large-scale scientific device, the construction and use costs are extremely high, and it cannot be commercialized
The spectral linewidth of terahertz quantum cascade lasers is too narrow, which limits its pulse time width and peak light intensity in pulse output mode
In summary, none of the existing methods can achieve continuously tunable, high-intensity THz pulse generation in the range of 0.1-30THz
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Embodiment 1
[0026] This embodiment takes diamond crystal as an example, the third-order nonlinear medium selected is a diamond single crystal, and its Raman resonance frequency ω v =2π×40THz, corresponding to 1332 wavenumbers (cm -1 ). The center frequency difference of the two beams of near-infrared pulsed light used to excite the Raman resonance should be equal to ω v .
[0027] Two beams of near-infrared pulsed light are generated by a tunable optical parametric amplifier.
[0028] The optical parametric amplifier is pumped by a titanium-doped sapphire femtosecond pulsed laser with a center wavelength of 800 nm.
[0029] It can be seen that when the wavelength of the signal light (signal) output by the optical parametric amplifier is 1.45 microns (ω 1 =2π×206THz), the center wavelength of the idler light (idler) should be 1.8 microns (ω 2 =2π×166THz).
[0030] At this time, the Raman resonance condition ω is satisfied 1 -ω 2 = ω v .
[0031] Since the output pulse width of th...
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The invention provides a method for generating coherent terahertz pulses based on resonance four-wave mixing, which comprises the following steps of: jointly acting three beams of pump light pulses on a third-order nonlinear medium to generate third-order nonlinear polarization of which the oscillation frequency is within a terahertz frequency range in the medium so as to generate a terahertz light pulse light source. When the instantaneous frequency difference of the two beams of incident pump light pulses is the Raman resonance frequency of the medium, the third-order nonlinear polarizability of a four-wave mixing process is enhanced by utilizing the Raman resonance transition of a medium. The three-order nonlinear polarizability in a four-wave mixing process is enhanced by utilizing the Raman resonance transition of the medium, and when the instantaneous frequency difference of the two beams of incident pump light pulses is equal to the Raman resonance frequency of the medium, the efficiency of the four-wave mixing process is remarkably improved. The method can generate high-intensity coherent terahertz pulses, and has the advantages that the output center frequency can be continuously adjustable in the 0.1-30 terahertz wave band, and the output spectrum bandwidth is adjustable.
Description
technical field [0001] The invention belongs to the field of optical technology, and in particular relates to a method for generating coherent terahertz pulses based on resonance four-wave mixing. Background technique [0002] Terahertz pulsed light sources have very important applications in optical research. Terahertz radiation lies between infrared light and microwaves on the electromagnetic spectrum, covering the frequency range of 0.1 to 30 terahertz. Due to the lower photon energy, electromagnetic radiation in this wavelength range can non-destructively probe general materials. At the same time, the intrinsic energies of elementary excitations in many materials are also in this frequency range, such as phonons, intermolecular vibrations, and molecular rotations. Coherent terahertz optical pulses have the characteristics of high peak electric field intensity and narrow pulse time width. Therefore, coherent terahertz optical pulses can be used for cutting-edge scienti...
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IPC IPC(8): H01S1/00
CPCH01S1/00
Inventor 田传山苏雨聃乐嘉明沈元壤
Owner FUDAN UNIV