研究目的
To demonstrate the first optical parametric oscillator (OPO) based on random phase matching using a disordered polycrystalline material, specifically ZnSe ceramic, to achieve ultra-broadband frequency conversion.
研究成果
The first OPO based on random phase matching in a disordered polycrystalline material (ZnSe ceramic) was successfully demonstrated, achieving a broad spectrum from 3 to 7.5 μm with a low pump threshold of 90 mW. This approach enables ultra-broadband frequency conversion and opens new avenues for generating few-cycle mid-IR pulses and multi-octave frequency combs using polycrystalline materials.
研究不足
The output intensity in RPM scales linearly with sample length, which is slower than the quadratic dependence for perfect phase matching, potentially limiting efficiency. The OPO outcoupling was not optimized, and the study used specific pump conditions (femtosecond pulses) that may not generalize to other regimes.
1：Experimental Design and Method Selection:
The experiment utilized a bow-tie ring OPO cavity design with synchronous pumping from a Kerr-lens mode-locked Cr:ZnS laser. Random phase matching (RPM) was employed to enable 3-wave interactions with large bandwidths, eliminating the need for orientation patterning.
2：Sample Selection and Data Sources:
A commercial ZnSe ceramic sample was processed via high-temperature annealing to increase the average grain size to be close to the coherence length (~100 μm). The sample was uncoated, plane-parallel polished, and
3：5 mm long, placed at Brewster angle. List of Experimental Equipment and Materials:
Equipment included a Cr:ZnS laser (62-fs pulse duration,
4：35 μm center wavelength, 650 mW average power, 79 MHz repetition rate), dielectric mirrors (M1 with >85% transmission at 35 μm and >95% reflection at 3-8 μm), gold-coated parabolic mirrors (M2 and M3 with 30° off-axis angle and 30 mm apex radius), gold-coated flat mirrors (M4 and others), a ZnSe wedge (3 mm thick) for outcoupling, and a piezo-actuator (PZT) for cavity-length control. Materials included the ZnSe ceramic sample. Experimental Procedures and Operational Workflow:
The OPO cavity was set up with mirrors and the ZnSe sample. Pump pulses were directed into the cavity, and the OPO output was measured. The cavity length was controlled using the PZT to optimize performance. Output spectrum and power were recorded.
5：Data Analysis Methods:
The output spectrum was analyzed to determine the spectral span and center wavelength. Pump threshold and depletion were measured, and conversion efficiency was calculated.
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