Recently, the team of Professors Zhiwei Lv and Zhenxu Bai at the Research Center for Advanced Laser Technology of Hebei University of Technology (HBUT), in collaboration with Ningbo Jingdrill Science and Technology Co. Ltd, has achieved a nanosecond Raman laser output with a peak power of greater than 1.5 MW using domestically-made large-size, optical-grade CVD single-crystal diamonds. This work is the first report of nanosecond pulsed Raman laser output with single pulse energy greater than 10 mJ, which reaches the highest international standard in terms of energy and peak power. The related research results were published in December 2023 as a newsletter in China Laser under the title of "Raman laser output with peak power of MW achieved in domestic diamond".
As an important "carbon material", diamond is not only the hardest naturally occurring substance, but also possesses extremely high thermal conductivity, a wide spectral transmission range, and high physical and chemical stability, and is known as the "hardest and sharpest industrial tooth" and the "ultimate semiconductor material". It is known as the "hardest and sharpest industrial tooth" and the "ultimate semiconductor material", and has been widely used in the fields of optical windows, diamond anvils, thermal management, polishing and grinding, and ionizing radiation detection. In addition, combined with its unique nonlinear optical properties, diamond lasers show extremely outstanding advantages in the field of Raman and Brillouin lasers, providing new opportunities for the development of high-power lasers.
Diamond crystals have extremely high Raman gain coefficients and the largest Raman frequency shifts among known crystals, so diamond Raman lasers are considered to be "a new path to break through the power and wavelength limits of lasers". In order to obtain highly efficient diamond laser operation with high beam quality, optical-grade synthetic diamond crystals need to be used as the gain medium. In order to achieve high efficiency and high beam quality, optical-grade synthetic diamond crystals are required as the gain medium, but most of the single-crystal diamond crystals used by researchers in their past studies have been imported. China is the world's largest producer of synthetic diamonds, especially in industrial-grade diamonds with international pricing power. Therefore, how to improve the quality and growth size of domestically produced single-crystal diamond crystals and maximize their application to the laser field is a key issue that needs to be broken through.
Fig. 1 Diagram of the experimental setup
Recently, the researchers utilized the domestically produced large-size optical-grade CVD single-crystal diamond (4×4×7 mm3) as the Raman gain medium, and obtained the Raman laser conversion with a wavelength of 1.2 μm and a single-pulse energy of 11.2 mJ by using a 1 μm pulsed laser as the pump source in an oscillator with a cavity length of only 15 mm. The output Raman laser pulse width was 7 ns, corresponding to a maximum peak power of 1.6 MW.
Figure 2 Raman laser output characteristics (a) energy curve (b) waveforms and spectra
This study reported for the first time the operation results of domestic diamond Raman laser under high power pumping, and the output peak power exceeded the megawatt scale for the first time, reaching the highest international standard. This result not only proves the significant improvement of domestic optical-grade diamond crystals in the process, but also provides new ideas for researchers to further break through the power limit of special wavelength lasers through diamond laser technology, as well as to expand its applications.
