基于飞秒锁模光纤激光脉冲基频光的差频产生红外光梳

报道了一种基于飞秒锁模光纤激光脉冲基频光的光纤型差频产生(DFG)红外光梳及其研制技术.基于自主研制的重频锁定200 MHz飞秒锁模掺铒光纤激光器,经啁啾脉冲光纤放大与超连续谱产生技术,优化近零色散OFS光纤(型号:OFS-980-20)长度,结合可调延时线,获得了精准同步的基频双色脉冲;以GaSe为非线性晶体,利用光整流技术,产生了可在6—10μm范围内宽带调谐的DFG红外光梳,光梳最大光谱宽度可达1.3μm.这种光纤型远红外光梳可望在分子光谱精密测量等领域发挥重要作用.

Fiber-type difference frequency generation infrared optical frequency comb based on the femtosecond pulses generated by a mode-locked fiber laser

Optical frequency comb (OFC) is a new type of high-quality laser source. The visible and near-infrared OFCs have become mature, and it has been widely used in optical frequency metrology, time/frequency transfer, precision laser spectroscopy and other fields. Since the mid and far-infrared spectral regions contain a large number of baseband absorption lines for molecules and the absorption intensities are several orders of magnitude higher than those in the visible and near-infrared spectral region, one has made great efforts to develop the mid and far-infrared OFCs in recent years. Although a variety of approaches to achieving infrared OFCs directly have been proposed, the method of difference frequency generation (DFG) infrared OFC based on the optical rectification technique is still more efficient. DFG infrared OFCs with widely tuning ability have been demonstrated based on fiber lasers so far. However, how to obtain the broadband spectrum for a DFG infrared OFC with widely tuning ability still needs to be solved. In this paper we report a fiber-type DFG infrared OFC by using the femtosecond pulses from a mode-locked erbium-doped fiber laser as the fundamental light. Based on the self-developed mode-locked fiber laser oscillator with repetition rate locked, the two-color fundamental pulse trains with the central wavelengths of 1.5 and 2.0 μm are respectively achieved after the chirped pulse fiber amplification and all-fiber supercontinuum (SC) generation techniques have been utilized. With a time-domain synchronous detection system based on the intensity autocorrelation principle, the accurate synchronization with the fundamental two-color pulses is obtained by optimizing the OFS compensated fiber length and adjusting a tunable optical delay line. Finally, by using the optical rectification technique, a fiber-type DFG infrared OFC is successfully generated with the help of a suitable designed GaSe nonlinear crystal. Our experimental results also show that the spectral location of the DFG infrared OFC can be tuned by controlling the spectral shape of the SC combined with the adjustment of the phase-matching for the nonlinear crystal. The measured tuning range of the DFG infrared OFC is from 6 to 10 μm, and the maximum spectral width is 1.3 μm. This fiber-type DFG infrared OFC may play an important role in the molecular spectroscopy, the atmospheric environmental monitoring, and other fields.