China's first product-level ytterbium-doped high-power femtosecond oscillator developed at Beijing Quantum Institute

Recently, the all-optical quantum source team of Beijing Institute of Quantum Information Science (BIIIS) has developed the first product-level high-power femtosecond oscillator in China, Fermion-007, which fills the gap of domestic watt-level femtosecond oscillators. Fermion-007 adopts several innovative technologies, and only one stage oscillator can output femtosecond pulsed laser with greater than 7W and heavy frequency of 80MHz, and its index and reliability have reached the international advanced level. At present, the R&D team has received orders for commercial cooperation in the field of ultrafast electron microscopy applications.

01Product and Performance Introduction

As the "seed" of femtosecond pulsed laser, Ultrafast femtosecond oscillator has the advantages of high re-frequency and high beam quality, but the output power is generally low and often requires power amplification to meet the application requirements. However, this "oscillator + amplifier" technology route will greatly increase the complexity of the system, resulting in higher costs and poor reliability, thus limiting the scope of the audience of femtosecond lasers. In addition, applications such as ultrafast electron microscopy and femtosecond two-photon microscopy have high requirements for laser repetition frequency, therefore, high-power femtosecond oscillators have become an urgent need in related fields.

Femtosecond oscillators are mainly divided into two categories: fiber optic and solid state. Solid-state oscillators, although more technically difficult, have a maximum output power three orders of magnitude higher than optical fibers, and have higher repetition frequency and longer mode-locked device life, which is the best technical solution to meet the application requirements.

Based on the above application requirements and technical route analysis, Beijing Quantum Institute has developed the Fermion series of high power all solid-state (DPSS) femtosecond oscillators. Without additional amplification, Fermion-007 can directly output femtosecond pulsed lasers larger than 7 W and 80 MHz with pulse width ~120 fs and central wavelength 1035 nm. In addition, the output laser has excellent beam quality and long-term stability with two-dimensional M2 less than 1.2 and 12-hour continuous operation power RMS value less than 0.3%.

Fermion-007 Spectrum and pulse width measurement

Fermion-007 Beam Quality and Long-term Stability

Fermion-007 adopts a number of engineering technologies such as low thermal resistance crystal package, integrated sealing, negative feedback control of temperature and humidity, and simulation optimization of cavity and cooling module design to reduce the negative impact of high pumping heat on the laser operating environment. The laser adopts Kerr-lens mode locking as the mechanism of femtosecond pulse generation and maintenance, which has a longer lifetime and higher device reliability than saturable absorber (SESAM). In addition, the R&D team has applied a new "RF synchronization technology" to Fermion-007 for the first time to self-start and maintain the femtosecond mode-locking state, which fundamentally overcomes the long-standing "lock-out" problem of Kerr-lens mode-locked femtosecond oscillators.

Fermion-007 Simulation of mechanical heat distribution and water circuit

02Key Applications and Project Collaboration

High-power femtosecond oscillators are widely used in the fields of two-photon microscopy imaging and optical parametric pumping. In recent years, with the development of related technologies, the market demand for such lasers is rapidly increasing for standardized instruments such as ultrafast electron microscopy and ultrafast electron diffraction.

Ultrafast electron microscopy (UEM) is a high-end analytical instrument upgraded from the traditional electron microscope, and the "femtosecond laser-driven photocathode" system is its new core module. The upgraded UEM not only has the spatial resolution at the atomic scale, but also has the ultra-high temporal resolution at the femtosecond-picosecond scale, which makes it a powerful tool for studying material dynamics processes.

Application of Fermion series products in ultrafast electron microscopy

The R&D team has carried out cutting-edge cooperation with relevant system vendors in the development of new ultrafast electron microscopes, and proposed for the first time the use of femtosecond oscillators to generate ultrafast electrons with high heavy frequencies to reduce the risk of damage to the photocathode caused by laser pulses. This solution is expected to fundamentally solve the long-standing photocathode reliability problem of such instruments and improve the lifetime and market competitiveness of ultrafast electron microscopy products. According to the estimation of the partner system vendor, the total market demand of ultrafast electron microscope can reach 50 units/year in the next 3 years.

03R&D Team Introduction

The high-power femtosecond oscillator is a research project led by Assistant Researcher Zijiao Yu of the All-optical Quantum Source Team of the Quantum Institute. The all-optical quantum source team was established in 2020 by Prof. Lu Wei and is affiliated with the Technology Industry Development Center of the Quantum Institute in Beijing. The team is dedicated to building key laser equipment related to supporting the quantum industry, including cutting-edge technology research, product development and industrialization of ultrafast and ultra-intense laser devices (TW-PW systems), laser accelerated desktop light sources and applications, and new high-end research femtosecond lasers.