High-energy Femtosecond Laser System Research Articles

High-energy femtosecond laser system based on a fiber laser seeder, Yb:YAG single crystal fiber and chirped volume Bragg grating

A high-energy chirped pulse amplification system based on a Yb doped fiber seeder, two-stage single crystal fiber (SCF) amplifier with a simple single-pass structure is demonstrated in this work. An amplified power of 52.2 W with a beam quality of less than 1.3 at 200 kHz is obtained, to our best knowledge, this is the highest power obtained with a single-pass amplification structure of the SCF with the energy of hundreds of microjoules. An excellent power stability of 0.32% is obtained. Dispersion between the chirped fiber Bragg grating (CFBG) stretcher and the chirped volume Bragg grating compressor is matched via the use of a self-made temperature tuning device of CFBG. As a result, a pulse duration of 740 fs and a compressed power of 31.4 W are obtained at a repetition rate of 200 kHz. In order to assess the influence of pulse duration induced by the nonlinearity during the amplification and increase the output pulse energy,the repetition rate of the self-made fiber seeder is changed to 100 kHz. A compressed power of 28.4 W and a pulse width of 858 fs are obtained, corresponding to a pulse energy of 284 µJ and a peak power of 331 MW. This compact and high-energy femtosecond laser system will find various applications in both scientific research and industrial implementation.

Stray light autocorrelation for the measurement of ultrashort laser pulses

Abstract Ultrashort laser pulses in the femtosecond range are of growing interest in medicine and micro material processing for industrial applications. The most interesting parameter is the pulse duration, which can only be measured by optical autocorrelation methods incorporating an optically nonlinear medium. Established methods mostly use monocrystalline beta barium borate (BBO) in transmission, exhibiting a high nonlinear conversion efficiency. However, this material is brittle, expensive and sophisticated in adjustment due to the necessary non-collinear phase matching. Since fiber-based high energy femtosecond laser systems become more and more achievable, the conversion efficiency of the nonlinear medium should no longer be seen as the restricting factor. Therefore, this research work discusses the suitability of several nonlinear media with differing translucency. Quartz, ammonium dihydrogen phosphate (ADP) and aluminum nitride (AlN) were compared in a standard autocorrelation setup and a novel versatile setup measuring frequency-doubled stray light. Best results were achieved with AlN, which appears to be a suitable and promising alternative material to BBO, reducing the expenses by two to three orders of magnitude.

Hybrid high energy femtosecond laser system based on Yb:YAG single crystal fiber amplifier

A hybrid high energy femtosecond laser system based on Yb:YAG single crystal fiber amplifier is experimentally studied. Due to the low nonlinearity and high gain of the Yb:YAG single crystal fiber, laser pulses with high energy of 146μJ at the repetition of 100KHz are obtained. The beam quality of 1.233 in the horizontal direction and 1.239 in the vertical direction is detected. After compression, pulses with the duration of 859fs and energy as high as 63.5μJ are achieved at 100kHz repetition rate in a compact size, this compact and simple laser system will find various applications in ultrafast laser micro-machining.

Indirect high-bandwidth stabilization of carrier-envelope phase of a high-energy, low-repetition-rate laser

We demonstrate a method of stabilizing the carrier-envelope phase (CEP) of low-repetition-rate, high-energy femtosecond laser systems such as TW-PW class lasers. A relatively weak high-repetition-rate (~1 kHz) reference pulse copropagates with a low-repetition-rate (10 Hz) high-energy pulse, which are s- and p-polarized, respectively. Using a Brewster angle window, the reference pulse is separated after the power amplifier and used for feedback to stabilize its CEP. The single-shot CEP of the high-energy pulse is indirectly stabilized to 550 mrad RMS, which is the highest CEP stability ever reported for a low-repetition-rate (10-Hz) high-energy laser system. In this novel method, the feedback frequency of the reference pulse from the front-end preamplifier can be almost preserved. Thus, higher CEP stability can be realized than for lower frequencies. Of course, a reference pulse with an even higher repetition rate (e.g., 10 kHz) can be easily employed to sample and feed back CEP jitter over a broader frequency bandwidth.

Chirally-coupled-core Yb-fiber laser delivering 80-fs pulses with diffraction-limited beam quality warranted by a high-dispersion mirror based compressor

We demonstrate a high-energy femtosecond laser system that incorporates two rapidly advancing technologies: chirally-coupled-core large-mode-area Yb-fiber to ensure fundamental-mode operation and high-dispersion mirrors to enable loss-free pulse compression while preserving the diffraction-limited beam quality. Mode-locking is initiated by a saturable absorber mirror and further pulse shortening is achieved by nonlinear polarization evolution. Centered at 1045 nm with 39-MHz repetition rate, the laser emits 25-nJ, positively chirped pulses with 970-mW average power. 6 bounces from double-chirped-mirrors compress these pulses down to 80 fs, close to their transform-limited duration. The loss-free compression gives rise to a diffraction-limited optical beam (M2 = 1.05).

Femtosecond laser technologies for linear collider designs

A highly stabilized high-energy femtosecond laser system was developed for Compton X-ray experiments. The laser system is based on the chirped pulse amplification, and each component is actively or passively stabilized. A master oscillator with less than 100fs timing jitter, two independent oscillators with 300fs relative timing lag, a new measurement technique of timing fluctuation of low-repetition amplified pulse, and a special designed regenerative amplifier with high quality beam were developed. New technical options for linear collider are proposed based on these expertises. The options are temporally square pulse for low emittance electron generation, a timing stabilized seeder for CO 2 amplifier, and multi-pulse high-energy lasers for γ–γ collision and for multi-bunch electron generation.