List of core components that China has not fully mastered in the field of ultrafast lasers
Ultrafast laser technology is based on other types of lasers. Taking a complex chirped pulse amplification system as an example, it integrates mode locking technology, dispersion control (time shaping) technology, thermal management technology, laser pulse amplification technology, pulse purification technology, and spatiotemporal quality control and diagnostic technology. Therefore, the required devices are diverse and a rich supply chain needs to be integrated. At present, no matter from the device level or the system level, even mainstream manufacturers, the West is in the lead. Taking only the titanium sapphire petawatt system, which represents scientific research applications, and the optical fiber and thin-film ultrafast laser systems, which represent industrial applications, as examples, we will make a core "catch-up list."
1. Chirp Mirror
Figure 1 Schematic diagram of the chirp mirror principle
As mentioned in the previous public article, the chirped mirror is the core component of the titanium sapphire wide-spectrum oscillator, and the titanium sapphire oscillator is the starting point and time center of the ultra-powerful laser. The high-quality chirped mirror ensures the mode-locking stability of the oscillator and the time quality of the pulse. At present, the best quality chirped mirror manufacturing technology is still in the hands of some German research institutes and companies, represented by Layertec and Ultrafast Innovations. Although there are several domestic research institutes developing and developing it, there are no mature commercial products yet.
2. Reflection and transmission grating
Figure 2 Large-diameter gold-plated reflection grating for pulse compressor
Grating is the core component of ultrafast laser and is used for pulse stretcher and compressor. At present, it is difficult to find high-quality suppliers in China, whether it is small-size gratings on the order of millimeters or large-size gratings on the order of several meters. The core technology is still mastered by France, Japan, Sweden and the United States. Typical representatives are J-Y, Horiba, Spectrogon, Ibsen, Lightsmyth and Polymouth and LLNL of the United States.
3. Large-size and high-quality Ti:sapphire crystal
Figure 3 Large-diameter Ti:sapphire crystal in petawatt laser
Ti:sapphire crystal is a wonder in the ultrafast field. Its spectral bandwidth, thermal performance and mechanical performance are far ahead of other crystals. Its position is irreplaceable in sub-20fs ultrafast oscillators and sub-100fs ultrafast amplifiers. Fortunately, the Shanghai Institute of Optics and Mechanics has made some key technological breakthroughs and is expected to further commercialize its products in the near future. However, overall, the American GTAT still monopolizes the global titanium sapphire crystal market.
4. Saturable semiconductor absorber mirror-SESAM
Figure 4 SESAM for mode-locked laser
SESAM, like the chirped mirror, is the core of the mode-locked laser and is mainly used for mode-locking of picosecond lasers. At present, competition in the picosecond laser industry has become increasingly fierce, and most of the mode-locking components used in its oscillators should be SESAM. At present, the core technology of SESAM is in the hands of Germany, with the German BATOP company as a typical representative. I believe that Swiss U Keller and his disciples should also master the core technology. After all, they are the originators of SESAM mode-locked laser.
5. Thin sheet laser module
Figure 5 Schematic diagram of thin sheet module
Thin sheet and optical fiber are typical technical solutions for industrial lasers. Due to its excellent thermal conductivity, thin sheet laser is one of the first choices for high repetition rate industrial lasers. At present, Germany's TRUMPF fully masters this technology, and its thin-sheet lasers have occupied most of the processing market. Germany's Stuttgart Laser Center and a few other German companies can also produce such modules, but their quality and market share are not as good as TRUMPF's. However, relevant domestic companies do not yet have the capability of thin-sheet laser technology.
6. Pulse shaper
Figure 6 Pulse shaper based on acousto-optic and liquid crystal spatial modulation
Utilizes the wide-spectrum characteristics of ultrafast lasers to perform spectral shaping to control pulse quality and shape. The current mainstream technologies are acousto-optic modulation and Fourier plane liquid crystal spatial light modulation. These two technologies are mastered by French Fastlite, American BioPhotonics, and Finisar. There should be research institutes in China that can produce experimental instruments, but there are still no products on the market.
7. Chirped fiber Bragg grating (CFBG) and volume Bragg grating (VBG)
Figure 7 Schematic diagram of CFBG and VBG principles
In Yb fiber lasers and solid-state laser amplification systems, CFBG and VBG are widely used in dispersion control to achieve pulse broadening and compression. The markets for these two devices are currently occupied by European and American companies, represented by Canada's Teraxion and the American Florida company Optigrate, which was just acquired by IPG.
8. Pockels cell and acousto-optic modulator
Figure 8 Schematic diagram of acousto-optic and electro-optic selector
These two devices are mainly used to select pulses in the amplification system, and the Pockels cell is used to import and export pulses in the regenerative amplifier. Currently, it is very difficult to find domestic high-quality brands that can be used in ultrafast lasers in China. European and American manufacturers still firmly control the market share.
9. Ultrafast laser technical talents
Figure 9 Professional technicians debugging titanium sapphire laser
As a side note, technology is the primary productive force, so talents are particularly expensive. However, in recent years, the manpower of ultrafast laser technology has not shown a growth trend, and the mainstream domestic institutes that train ultrafast laser talents cannot guarantee that most of them will continue to engage in the development of ultrafast laser technology. Many even test the waters across fields, resulting in an extreme shortage of talents in this field. We appeal again, hoping that more young people will join this field, or provide services, or provide technology, or engage in scientific research, to help the ultrafast laser industry!