Studies On Femtosecond Parametric Up-conversion And Down-conversion Generation And Amplification

In nonlinear medium, many parametric processes are caused by sum frequency and difference frequency. Traditionally, both optical parametrical amplification (OPA) technology and optical parametric chirped-pulse amplification (OPCPA) technology are based on difference frequency. Generally, the fundamental femtosecond pulses from oscillator or regenerative amplifier are infrared ray (IR) or near IR. In order to obtain the tunable femtosecond visible or ultraviolet laser, second harmonic or third harmonic of the fundamental beams are usually used as the pump source, or the output of the optical parametric down conversion amplification are doubled or tripled. However, the conversion efficiency of the second harmonic or third harmonic generation is very low for femtosecond wide-band laser pulses. It is challenging to achieve the optical parametrical amplification (OPA) and the optical parametric chirped-pulse amplification (OPCPA) based on parametric up conversion. In this paper, the parametric up conversion and down conversion generation and amplification has been theoretically and experimentally investigated. There are several advances as follows:1. The actuality and development of femtosecond optical parametrical generation and amplification are systematically reviewed. The principle and technology of femtosecond optical parametrical amplification and the optical parametric chirped-pulse amplification are introduced and valued.2. The mechanism for spontaneous parametrical down conversion and parametrical up conversion emission are theoretically discussed. The coupled wave equation has been solved to express the parametrical down conversion and parametrical up conversion processes. The light field autocorrelation and cross-correlation and the intensity correlation have been calculated. The spontaneous parametric photon quantum efficiency has been calculated and analyzed with the Wigner representation.3. Spontaneous parametric down conversion and up conversion conical emissions are experimentally observed with the fundamental pump source at 800nm, and their phase matching conditions are obtained. Especially, the generation of the spontaneous parametrical up conversion conical emission without second harmonic generation is firstly achieved and reported.4. In the experiment, a pair of coherent parametric beams is firstly achieved with two-photon excitation. Its interference is observed. Moreover, at the same time, optical parametric generation and amplification is achieved with SHG pump source based on parametric down conversion process.5. The parametric up conversion amplification without SHG has been experimentally achieved for the first time. Several coherent light beams and parametric rings at different wavelengths have been observed, and their mechanisms for the above-mentioned parametric processes are theoretically and experimentally discussed.6. The mechanisms of parametric up conversion amplification without SHG, parametric down conversion amplification with SHG and two-photon excited coherent parametric generation are interpreted by semiclassical theory, and their phase matching conditions in the nonlinear medium have been comprehensively and analyzed and compared.