Science Island team has made progress in high efficiency lithium niobate acousto-optic Q-switching technology for mid infrared laser

Recently, the research team of Jiang Haihe, a researcher in the Medical Laser Technology Laboratory of the Institute of Health of the Chinese Academy of Sciences, cooperated with China Electronics Technology Group, and made important progress in the research of acousto-optic Q-switching technology in the mid infrared band: the lithium niobate (LiNbO3) crystal acousto-optic switch was realized for the first time, and its performance in 2.79 μ High efficiency Q-switched output in mEr, Cr: YSGG laser. Relevant achievements have been published in the international optical journal Optics Letters.

Acousto optic modulators are widely used in lasers as Q-switching switches to obtain high repetition rate, narrow pulse width laser output. Although 3 μ Several acousto-optic Q-switches in m-band have achieved preliminary results, but the acousto-optic medium and transducer are usually made of different materials, which puts forward higher requirements for the fabrication process of devices and increases the energy loss during ultrasonic propagation. Therefore, it is necessary to use the same material of acoustooptic medium and transducer to make a modulator with excellent performance and simple fabrication process.

Lithium niobate crystal is a traditional multifunctional crystal. In recent years, lithium niobate thin film photonics devices with extremely low optical loss and rich photoelectric functions have been developed rapidly. Lithium niobate is expected to replace silicon materials in the field of integrated photonics, providing solutions to the bottleneck problem of high power consumption and slow speed in the communication field. Since the discovery of lithium niobate crystal in 1937, although it has good acousto-optic characteristics and has been used as a transducer material for a long time, it has not been able to achieve laser acousto-optic Q-switch of block crystal. This research has realized the homogeneity and integration of acousto-optic medium and transducer, which can simplify the manufacturing process, reduce the auxiliary cost, and also reduce the loss of ultrasonic energy, so that the diffraction efficiency of lithium niobate acousto-optic Q-switch can reach 57% (Figure 1), and lithium niobate crystal has a high damage resistance threshold (>200 MW/cm2).

Fig. 1 Diffraction efficiency curve of lithium niobate acousto-optic Q-switch versus driving power

Self developed 2.79 μ The m Er, Cr: YSGG acousto-optic Q-switched laser has verified that the designed lithium niobate acousto-optic Q-switch has good acousto-optic Q-switched performance (Figure 2). At a high repetition frequency of 50 Hz, a laser output with a pulse energy of 17.6 mJ, a pulse width of 55.2 ns, and a peak power of 319 kW has been obtained. The developed Er, Cr: YSGG lithium niobate acousto-optic Q-switched laser can achieve stable and high peak power laser output.

Figure 2. Curve of Pulse Energy and Pulse Width Changing with Pump Energy when PRF=50 Hz

This study shows that lithium niobate crystal has high diffraction efficiency, high damage threshold and good acousto-optic Q-switching performance, which is 3-5 μ A new acoustooptic switch for high power laser in m mid infrared band. At the same time, this study is a step forward to explore the possibility of direct bonding synthesis of homogeneous materials into integrated acoustooptic devices.

Source: Hefei Institute of Material Science, Chinese Academy of Sciences