Understand 10w Ultraviolet lasers technology in one article

Interest in short-wavelength continuous ultraviolet (UV) light sources has grown over the past decade. The ultraviolet laser with a wavelength range of 200-280 nm and continuous output has the advantages of short wavelength, large photon energy, small diffraction effect, strong resolving power, and small thermal effect.

Short-wave UV lasers are very suitable for scientific research, industry, and OEM system integration development, and can be used for fluorescence absorption, Raman spectroscopy, genetic testing, coherent measurement, biochemical, medical diagnosis and treatment, food safety, rapid prototyping, precision micromachining, 3D printing and other applications Provide the ideal light source. The data storage space of disks produced based on short-wave ultraviolet lasers is 20 times higher than that of blue-light lasers. Therefore, Japanese computer hardware manufacturers are working hard to apply short-wave ultraviolet lasers and short-wave ultraviolet laser tubes to computer data storage technology in order to greatly increase the data storage capacity.

The reason why short-wave ultraviolet lasers are superior to infrared lasers and visible lasers is that short-wave ultraviolet lasers can directly destroy the chemical bond processing substances that connect the atomic components of substances without destroying the surrounding environment. Typically, CW UV laser applications use conventional gas laser technology or mode-locked solid-state laser technology, but only provide quasi-CW performance. The peak power produced by these mode-locked lasers is usually in the kilowatt range, which severely limits the application of short-wave UV lasers in the biological field.

All-solid-state solid-state laser technology pumped by laser diodes in the past decade has not only increased power, optimized mode quality, but also resulted in better directional stability. Compared with other types of lasers, it has the characteristics of high efficiency, reliable performance, better beam quality and stable power.

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In the future, short-wave ultraviolet laser technology will lead to the development of a new generation of nanotechnology, materials science, biotechnology, chemical analysis, plasma physics and other disciplines. From short-wave ultraviolet laser to infrared laser, optoelectronic technology will become an important basis for human development, and short-wave ultraviolet laser technology is becoming a new research and application hotspot.

261nm shortwave CW UV laser technology

Traditional way of generating short-wave UV laser lines

Due to the high energy of short-wave ultraviolet photons, it is difficult to generate a certain high-power continuous short-wave ultraviolet laser through the excitation of an external excitation source. Therefore, the short-wave continuous ultraviolet laser is generally generated by the nonlinear effect frequency conversion method of crystal materials. There are generally two methods for traditional all-solid-state short-wave UV laser spectral line generation:

Directly perform 3 or 4 frequency doubling of the infrared all-solid-state laser in the cavity or outside the cavity to obtain the short-wave ultraviolet laser spectrum;

First use the frequency doubling technique to obtain the second harmonic, and then use the sum-frequency technique to obtain the short-wave ultraviolet laser spectrum. If the 1064 nm fundamental frequency light radiated by the Nd:YAG/Nd:YVO4 laser crystal is used for frequency doubling to output 532 nm laser light, the 1064 nm fundamental frequency light and the 532 nm frequency doubled light need to be used as new fundamental frequency light to pass through the nonlinearity again. The process outputs a 355 nm UV laser. Usually, the effective nonlinear coefficient is small and the conversion efficiency is low.

Trivalent praseodymium ion (Pr3+) has attracted much attention as a rare-earth element ion that can directly achieve visible light output through downconversion, and its energy level transition is shown in Figure 1. Pr3+-doped materials can produce visible light in several colors, including deep red (approximately 698 nm and 720 nm), red (approximately 640 nm), orange (approximately 605 nm), green (approximately 522 nm), and blue (approximately 522 nm). 490 nm). With the development of InGaN semiconductor lasers, high-power, compact all-solid-state lasers can be realized in the visible light band. Another advantage of this visible-light laser is that it can generate continuous short-wave UV lasers through intracavity frequency doubling.

Technical scheme for realizing short-wave ultraviolet output laser mode by single frequency doubling

Short-wave continuous ultraviolet lasers must rely on resonators to achieve continuous and stable output of ultraviolet lasers, which requires higher requirements for resonator design, mode matching, light-to-optical conversion efficiency, and damage resistance of optical films, and is technically difficult. In order to overcome the shortcomings of the existing technology, Changchun New Industry Optoelectronics Technology Co., Ltd. provides a laser mode that realizes short-wave ultraviolet output by single frequency doubling, which can convert fundamental frequency light into frequency doubled light output through a second nonlinear process, and then realize A truly high-efficiency output laser diode directly pumps an intracavity frequency-doubling short-wave UV all-solid-state laser. The technical solutions adopted are as follows:

By optimizing the parameters of the optical resonator cavity type, cavity length and mirror curvature, an optical structure that meets the design input requirements is designed;

By optimizing the design of optical thin films, high-quality optical thin films are fabricated by ion sputtering deposition method. Combined with the actual debugging effect, continuously improve the coating quality of optical crystals and lenses, reduce the loss in the cavity, improve the output efficiency of the laser, and provide conditions for the stable resonance of the laser wavelength;

By optimizing parameters such as laser medium and nonlinear crystal material, concentration, length, etc., the best output can be achieved;

By optimizing the mechanical structure design, it is more convenient to fix the laser components; optimizing the modular structure design without installation and adjustment, so that the industrial-grade reliability is continuously increased; reducing the volume of the light source module and strengthening the thermal damage resistance of continuous operation; improving the optical-mechanical structure Anti-vibration ability and device service life to ensure the quality of laser products;

The electrical laser power supply and temperature control circuit adopt digital technology to realize the design functions of small size, low noise and anti-interference. Through the photoelectric feedback technology, the self-adaptive adjustment of the output power of the laser is realized, and the long-term stability and reliability of the laser are improved.

Through key technologies such as short-wave CW UV laser pump source integration, resonator design, mode matching, nonlinear frequency conversion, and optical film fabrication, breakthroughs in technical problems such as continuous operation, high efficiency, and high-power long-term stable operation of short-wave UV lasers

Intracavity frequency-doubled short-wave ultraviolet all-solid-state laser

The laser is a laser diode directly pumped intracavity frequency-doubling short-wave ultraviolet all-solid-state laser, as shown in Figure 3. It is mainly composed of semiconductor laser (LD), pumping optical shaping mirror, pumping optical coupling mirror group, laser gain medium (Pr3+ crystal), nonlinear frequency doubling crystal (BBO) and two plano-concave mirrors. The laser uses a folded V-shaped resonator.

Folded resonators can provide two optimal beam waists, in nonlinear crystals and in laser gain media, respectively. One beam waist can satisfy the mode matching condition, and the other can improve the frequency doubling efficiency. The LD emits laser light with a wavelength of 444 nm corresponding to the absorption of the Pr3+ crystal, and the optical distribution of the LD is shaped by the pumping optical shaping mirror group, and then injected into the Pr3+ crystal through the pumping optical coupling mirror group. The transparent surfaces of the Pr3+ crystal are parallel to each other and coaxial with the resonator.

The nonlinear crystal BBO doubles the frequency of the 522 nm fundamental frequency light in the cavity to realize an all-solid-state, continuous 261 nm short-wave ultraviolet laser output. Folded resonators can be made very compact, resulting in mechanical stability. Generation of the entire second harmonic (SHG) is achieved by resonator mirror reflection in one direction without the additional risk of UV light passing through the gain material, preventing its optical degradation. In addition, Pr3+ crystals, nonlinear crystals and LDs are all strictly and precisely temperature controlled with a semiconductor cooler (TEC) to achieve stable operation of the laser.

Since both the laser crystal and the frequency conversion crystal have a certain damage threshold, the UV frequency conversion crystal is easily damaged by ultraviolet light during use. The area of ​​the crystal destroyed by the ultraviolet beam only accounts for a small part of the crystal cross-sectional area, but the laser still needs to be repaired or replaced, which causes a lot of waste of manpower and material resources, and shortens the overall service life of the solid-state ultraviolet laser. Can not meet the requirements of long-term stable operation.

RFH LASER improves the lifetime of high power UV lasers. Based on the design of the resonant cavity, frequency doubling control, thermal compensation in the cavity and cooling control, etc., by adding a deflection mechanical device in the resonant cavity, during the use of the laser, the frequency doubling crystal is shifted at intervals to avoid the long-term effect of the optical path. At the same point on the frequency-doubling crystal, the service life of the short-wave ultraviolet laser is doubled.

UV-F-261 is a continuous operation laser in the short-wave ultraviolet 261 nm band. Its center wavelength is 261.37 nm, the laser output power exceeds 100 mW, the laser power stability is better than 1%, and the laser amplitude noise is better than 0.5 %. The laser has the characteristics of excellent laser performance (including laser power, stability, beam quality, service life, etc.), simple structure, and strong environmental adaptability (including shock resistance, high temperature resistance, moisture resistance, etc.).

Short-wave ultraviolet lasers are emerging as new applications in the field of Raman spectroscopy. Ultraviolet Raman spectroscopy avoids fluorescence interference, has high sensitivity, and the Raman signal can be enhanced by the resonance Raman signal, which is largely broadened. Applications of Raman spectroscopy in the fields of physics, chemistry, biology, and materials. The group of Academician Li Can of the Dalian Institute of Chemistry, Chinese Academy of Sciences used UV-F-261 short-wave continuous ultraviolet laser for the structure, synthesis, catalytic characterization and in-situ characterization of molecular sieves and heteroatom molecular sieves, and achieved important results.

Application of Laser in Ultraviolet Raman Spectrometer and Ultraviolet Raman Spectroscopy

At present, it is known that the development of 261 nm short-wave continuous ultraviolet laser is being carried out in China. This product can meet the needs of deep ultraviolet Raman spectroscopy, ultraviolet lithography, fluorescence excitation and other fields, fill the market gap, and promote the development of laser fine processing, spectral analysis and other fields.