Wide-tuned, narrow-spectrum-wide mid-infrared optical parameter research gains further progress

May 03, 2024

China Instrument Network Instrument R&D Recently, the research group of Jianghaihe Researcher of the Medical Physics and Technology Center of the Hefei Institute of Physical Science, Chinese Academy of Sciences has made progress in the research of wide-tuned, narrow-spectrum mid-infrared light parameters. The relevant research results are published in the international optical journals. Optics Express (Optics express 25.25 (2017): 31810-31815).

The 3-5 μm mid-infrared laser has a wide range of applications in atmospheric environment monitoring, target feature detection, and high-resolution spectroscopy. Narrow-line-width tunable lasers are ideal sources for such applications. Optical parametric oscillation (OPO) is an effective technique for achieving wide-tuned mid-infrared coherent laser output. However, under normal circumstances, the spectral width of the pulsed mid-infrared laser output by the free-running OPO is relatively wide, generally as high as tens of nanometers or even hundreds of nanometers, which severely limits the wide application of the infrared light source in the OPO. In order to compress the output spectrum width of the OPO, a frequency-selective element such as an intracavity insertion etalon or VBG is usually used. However, a large extra loss is introduced, which not only results in an increase in the OPO oscillation threshold, but also reduces the conversion efficiency of mid-infrared lasers. Among them, the use of VBG frequency-selective components also severely limits the wavelength tuning range of OPO. Therefore, wide tuning, narrow bandwidth and wide efficient OPO laser has become a hot spot in the research of mid-infrared laser technology.

In response to the above problems, the researchers of this research group have worked hard for many years. Firstly, the single-longitudinal-mode pulsed fiber laser pumped PPMgLN-OPO to obtain a high efficiency mid-infrared laser output. The etalon design was used as an OPO cavity mirror to effectively modulate and control the gain spectrum width of the oscillating signal light. At the same time, seed self-injection technology and double-solid etalon coupling cavities were used to further suppress the weak sideband of the oscillating signal, achieving a narrow-spectrum-wide signal optical oscillation and performing the single-longitudinal mode pumping light in the cavity. With effective interaction, a narrow-spectrum-wide OPO mid-infrared laser output was obtained. In the experimental results, the spectral width of the idler light is narrowed to 0.36 nm, which is about 2 orders of magnitude improvement over the free oscillation spectral width suppression ratio. At the same time, the wavelength tuning range reaches 200 nm, and the maximum output power is 2.6 W. The corresponding light-to-optical conversion efficiency is 17.4%, making it the most effective technical method for the narrow linewidth of this band.

The quasi-phase-matching technique used in this experiment has the advantages of high-gain, wide-tuning, etc., of the periodically poled crystal MgO:PPLN. The pump source 1μm fiber laser has high stability and compactness, and the developed OPO mid-infrared laser output has a high peak value. The power and low threshold lay the foundation for the wide-tuned, narrow-spectrum-width, high-efficiency OPO mid-infrared laser applications.

The research work was funded by the National Natural Science Foundation of China and the China Academy of Sciences’ Strategic Pilot Science and Technology Project.

(Original title: The Medical Physics Center has made further progress in the study of wide-tuned, narrow-spectrum mid-infrared light parameters.)

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