Junjie Chi

\(Q\) -Switched Mode-Locked Nd:YVO 4 Laser by Topological Insulator Bi 2 Te 3 Saturable Absorber

By using a reflection type of topological insulator Bi₂Te₃ as saturable absorber that was prepared by a hydrothermal intercalation/exfoliation method, we have demonstrated the stable Q-switched mode-locked operation of Nd:YVO₄ solid-state laser. Its maximum output power can reach up to 247 mW with respect to the absorbed pump power of 6.39 W. To the best of our knowledge, this is the first report for passively Q-switched mode-locking Nd:YVO₄ solid-state laser at 1-μm wavelength using a topological insulator Bi₂Te₃ as saturable absorber. In the experiment, we have also observed the stable Q-switched operation with pulse width as short as 2 μs, output power 183 mW, and repetition rate up to 151.5 kHz.

980-nm all-fiber mode-locked Yb-doped phosphate fiber oscillator based on semiconductor saturable absorber mirror and its amplifier*

A 980-nm semiconductor saturable absorber mirror (SESAM) mode-locked Yb-doped phosphate fiber laser is demonstrated by using an all-fiber linear cavity configuration. Two different kinds of cavity lengths are introduced into the oscillator to obtain a robust and stable mode-locked seed source. When the cavity length is chosen to be 6 m, the oscillator generates an average output power of 3.5 mW and a pulse width of 76.27 ps with a repetition rate of 17.08 MHz. As the cavity length is optimized to short, 4.4-mW maximum output power and 61.15-ps pulse width are produced at a repetition rate of 20.96 MHz. The output spectrum is centered at 980 nm with a narrow spectral bandwidth of 0.13 nm. In the experiment, no undesired amplified spontaneous emission (ASE) nor harmful oscillation around 1030 nm is observed. Moreover, through a two-stage all-fiber-integrated amplifier, an output power of 740 mW is generated with a pulse width of 200 ps.

10.5 W single-beam-output passively mode-locked Nd:YVO4 oscillator end-pumped by 808nm laser diode

We demonstrate a 10.5 W passively mode-locked Nd:YVO4 oscillator end-pumped by 808 nm laser diode. A novel resonator structure with large mode field space is introduced to solve thermal lens effect and semiconductor saturable absorber mirror’s (SESAM) damage, and then we achieve a single-beam-output picosecond pulse laser without inserting any other laser output elements in laser resonator. The repetition rate of mode-locked pulse is 63.4 MHz with 12.9 ps pulse width, corresponding to maximum pulse energy of 166 nJ and peak power of 12.9 kW. In addition, we discover a complete evolution process of pulses from Q-switched mode-locking to continuous wave (CW) mode-locking for the first time.

High-energy, high-peak power single-frequency 10 ns pulsed fiber amplifier

We have demonstrated an all fiber, single-frequency 10 ns pulsed high energy and high peak power amplifier. It was capable of reaching 4.6 mJ pulse energy (460 kW peak power) and 2.3 mJ pulse energy (230 kW peak power) respectively for 10 ns pulses corresponding to the repetition rate of 5 kHz and 10 kHz. In the power amplifier stage, we used the large-mode-area fiber to avoid the nonlinear effects such as SBS.

Sub-picosecond double-clad photonic crystal fiber oscillator and amplifier system

A ytterbium-doped large mode area PCF sub-picosecond laser oscillator and amplifier system is experimentally studied. The oscillator which combines NPE and SESAM is operating on the all-normal-dispersion regime and the LMA PCF is used as the gain medium. In the CW mode-locking regime, the oscillator directly generates the pulse at the repetition rate of 83.7 MHz while the pulse duration is 960 fs. The double-clad fiber amplifier system directly generates a high average power of 12.53 W with a pulse duration of 4.1 ps corresponding to the pulse energy of 150 nJ and peak power of 36.6 KW after about 3 m ytterbium doped double clad fiber amplification.

980 nm narrow linewidth Yb-doped phosphate fiber laser

A narrow-linewidth ytterbium (Yb)-doped phosphate fiber laser based on fiber Bragg grating (FBG) operating around 980 nm is reported. Two different kinds of cavity are applied to obtain the 980 nm narrow-linewidth output. One kind of the cavity consists of a 0.35 nm broadband lindwidth high-reflection FBG and the Yb-doped phosphate fiber end with 0° angle, which generates a maximum output power of 25 mW. The other kind of resonator is composed of a single mode Yb-doped phosphate fiber and a pair of FBGs. Over 10.7 mW stable continuous wave are obtained with two longitudinal modes at 980 nm. We have given a detailed analysis and discussion for the results.

LD pumped high-repetition-rate high-power 532nm Nd:YAG/LBO solid state laser

Diode pumped solid state 532 nm green laser is widely required for many industrial, medical and scientific applications. Among most of these applications, high power quasi-continuous-wave (QCW) green laser output is demanded. This can be efficiently achieved through a diode-side-pumped acoustic-optic Q-switched Nd:YAG laser with an intracavity second harmonic generation (SHG). In our experiment, LBO crystal is used for the second harmonic generation of high-average-power lasers of near infrared (NIR) range, though its effective NLO coefficient deff is relatively small. It is because of its high damage threshold (greater than 2.5 GW/cm2), large acceptance angle, small walk-off angle, and the nonhygroscopic characteristic. In this paper, we reported a high-repetition-rate high-power diode-side-pumped AO Q-switched Nd:YAG 532 nm laser. A plane-plane cavity with two rods, two AO Q-switches and the type II critical phase-matched LBO at room temperature were employed. Under the LD pump power of 480 W, 95.86 W at 1064 nm wavelength was achieved when the repetition rate was 15 kHz, and the 532 nm average output power of 44.77 W was obtained, with a pulse width of 111.7 ns, corresponding to an optical to optical conversion efficiency of 46.7% from 1064 nm to 532 nm. The 532 nm average output power was 40.10 W at a repetition rate of 10 kHz with a pulse width of 78.65 ns. The output characteristics of the SHG varying with the pumping current and the pulse repetition frequency (PRF) of the laser were also investigated. Further improvement of the SHG is under study.

Sub-nanosecond all-normal-dispersion mode-locked Yb-doped fiber oscillator and its amplifier

We report two different pulse widths sub-nanosecond mode-locked Yb-doped fiber laser oscillators and a high power all-fiber master oscillator power amplifier (MOPA). Firstly, a 24.2 m long-cavity all-fiber mode-locked nanosecond laser oscillator has been demonstrated. Stable nanosecond pulses are achieved through nonlinear polarization rotation mode-locking technique rather than conventional methods. The pulse width is 1.1 ns and the central wavelength is 1042 nm with 3-dB bandwidth of 9.8 nm. Meanwhile the laser oscillator’s maximum average output power is 79.4 mW with repetition rate of 8.5 MHz, corresponding to pulse energy of 9.3 nJ. Secondly, a sub-nanosecond mode-locked Yb-doped fiber laser oscillator is achieved only by changing the laser cavity to 7.8 m. It produces 104.3 mW maximum average output power with 26.2 MHz repetition rate at 1042 nm. Pulse width is 0.55 ns with single pulse energy of 4.0 nJ. Finally, we adopt the second laser oscillator as a seed source of MOPA. 10.5 W average output po...

A Quasi-Three-Level Acousto-Optics (AO) Q-Switched Yb-Doped Double Clad Photonic Crystal Fiber Laser

We demonstrate a acousto-optics (AO) Q-switched 980 nm Yb-doped photonic crystal fiber (PCF) laser, which generated an average output power of 731 mW from single end of the fiber when the fiber length was 30 cm. The laser pulse of 40 ns and pulse repetition frequency of 6 kHz was detected. This Q-switched 980 nm PCF laser reached a peak power of 3 kW. The linewidth of the laser was 3.5 nm arranging from 977 nm to 980.5 nm. A fiber coupled diode laser with the center wavelength of 915 nm was used as the pump source for the 980 nm pulsed PCF laser.

A simple all-normal-dispersion mode-locking laser based on large-mode-area Yb-doped Photonic crystal fiber

Stable mode-locked operation in a simple normal-cavity dispersion laser oscillator that consists of only Yb-doped Photonic crystal fibers (PCFs) and SESAM saturable absorber is studied. Without any discrete dispersion compensation components or conventional spectral filters, the SESAM works with the strongly chirped pulse. The laser generates 55 nJ stable mode-locked pulses with 45.2 MHz fundamental repetition rate at 1030.8 nm central wavelength. This kind of mode-locked fiber oscillators can compete in terms of pulse energy and peak power with most advanced bulk solid-state Ultra-short pulsed lasers.