Jun Enokidani

Efficient UV generation of a Yb-fiber MOPA producing high peak power for pulse durations of from 100 ps to 2 ns

We demonstrate an average ultraviolet (UV) power generation of 20 W by harmonically converting the output of an all-fiber master oscillator power amplifier (MOPA) system. The third-harmonic generation (THG) UV output provides a conversion efficiency of 40% from the amplified fundamental output. The seed source, which consists of a 1064-nm-wavelength continuous-wave laser diode and two cascaded intensity modulators, produces chirp-free pulses with tunable durations from 100 ps to 2 ns at arbitrary repetition rates and a high dynamic extinction ratio. The fiber MOPA system generates a maximum average power of 50 W and a maximum peak power of 83 kW.

Tunable pulse width and multi-megawatt peak-power pulses from a nonlinearly compressed monolithic fiber MOPA system

We report on tunable pulse width and high peak power pulse generation from a nonlinearly compressed monolithic fiber MOPA system. The master seed source employs a Mach-Zehnder intensity modulator (MZIM). This seed source has operational flexibility with respect to pulse width, 90 ps to 2 ns and repetition rate, 200 kHz to 2 MHz. The seed pulses are amplified by a monolithic three-stage amplifier system based on polarization maintain Yb-doped fibers. The maximum output power was 32 W at the shortest pulse condition, the pulse width of 90 ps and the repetition rate of 750 kHz. A spectral width after amplification was broadened to 0.73 nm at RMS width. Both of ASE and SRS are not observed in the spectrum. After amplification, we also demonstrated pulse compression with a small piece of chirped volume Bragg-grating (CVBG) which has the dispersion rate of 81 ps/nm. As a result of pulse compression, the shortest pulse width was reduced from 90 ps to 3.5 ps, which brought an increase of the peak power up to 3.2 MW. The compressed pulses are clean with little structure in their wings. We can expand the operation range of the monolithic fiber MOPA system in pulse width, 3.5 ps to 2 ns.

Compression of picosecond pulses with a chirped volume Bragg grating

We demonstrate the pulse compression of the picosecond laser system with an all fiber master oscillator power amplifier configuration containing a chirped volume Bragg grating (CVBG) at 1064 nm. We use a passive mode-locked Yb doped fiber laser with a 10 ps pulse width at a 45 MHz repetition rate for the master oscillator. Optical pulses from the oscillator are amplified by a single stage fiber amplifier. Then the spectra of amplified pulses are chirped, and the spectral widths spread due to self phase modulation (SPM) in the fiber amplifier. The chirped pulses are compressed by CVBG. In this system, we achieve the pulse width of 2.89 ps, and average output power of 1.3 W.

75kW peak power 50ps pulsed fiber laser system

High power pulsed lasers are used for industrial applications. The pulse width extends over from the range of μs regime to fs regime, and the maximum repetition rate is around 100 MHz. A function in which pulse width and repetition rate can be changed independently is desired with many applications.

Enhancing dynamic extinction ratio of a fiber-based seed source

We report enhancing dynamic extinction ratio (DER) of a fiber-based seed source. The seed source consists of a waveguide Mach-Zenhder intensity modulator (MZIM) and a 1064 nm-wavelength continuous wave laser diode. The phase drift in MZIM is stabilized by a feed back bias control system. As a result we achieved a DER of 39 dB at 2 ns pulse duration and 200 kHz pulse repetition rate. The seed pulses were followed by an acoustic optical modulator (AOM) in order to enhance DER by a factor of 105 and amplified by the fiber amplifier with a factor of 2×104. We demonstrated the second harmonic generation (SHG) of the amplified pulses with a Periodically Poled Lithium Tantalate crystal (PPLT). As a result of DER enhancement a higher conversion efficiency of SHG was achieved when the AOM is working.

Polarization-maintaining amplifier based on 3C fiber structures

Chirally-Coupled-Core (3C) fiber structure can preserve a single mode quality and even a linear polarization for a large core size. A principal advantage of fiber laser is its compatibility with monolithic integration and robust system. But so far, devices such as a combiner using the 3C fibers have not been reported. Here we report the first demonstration of such monolithic amplifier structure which contains an active fiber and a combiner based on 3C fibers. A single-stage amplifier is seeded by an EO Q-switched micro-laser and pumped by two high power fiber pigtailed 976-nm laser diodes via an in-house fabricated (2 + 1) × 1 pump signal combiner. The active fiber is based on a 3-m-long, 3C Yb-doped fiber (33 μm/250 μm core/cladding diameter with 0.06/0.46 NA). The amplifier demonstrates scaling up to 30W average power and 150 kW peak power in 0.3mJ, 2ns pulses. The beam profiles and beam qualities were characterized as its output power was varied up to 30W. The beam profile was maintained at a high beam quality of around M2=1.2. The spectral properties of the 3C fiber were also characterized as its output peak power was varied.

Compression of chirp pulses from a picosecond fiber based amplifier

We demonstrate the pulse compression of the picosecond laser system with an all fiber master oscillator power amplifier configuration containing a chirped volume Bragg grating (CVBG) at 1064 nm. We use a passive mode-locked Yb doped fiber laser with a 10 ps pulse width at a 45 MHz repetition rate for the master oscillator. Optical pulses from the oscillator are amplified by a single stage fiber amplifier. Then the spectra of amplified pulses are chirped, and the spectral widths spread due to self phase modulation (SPM) in the fiber amplifier. The chirped pulses are compressed by CVBG. In this system, we achieve the pulse width of 2.89 ps, and average output power of 1.3 W.

Reserch on picosecond passively Q-switched microchip laser

Compact and simple pico second lasers are required in many applications like fine material processing. we have been developing a pulsed fiber laser which consist of a fiber amplifier system and a passively Q-switched microchip laser as a seed source. In this presentation, we report the test results of the passively Q-switched microchip laser. The pump source is a diode laser coupled to single mode fiber with the wavelength of 808 nm and the maximum power of 214 mW. The microchip is composed of a combination of gain medium and a saturable absorber, and we used two types of microchip. There are differences in the thickness of the gain medium and dopant ratio of neodymium. The gain medium is Nd:YVO4. The thickness are 100 μm with 3% neodymium doping and 300 μm with 2% neodymium doping. As a result, We obtained 6.1 mW laser output with 90 ps pulse width, 1.3 MHz repetition frequency at short gain medium. And the other one got 14 mW laser output power with 161ps pulse width, 1.4 MHz repetition frequency. The single longitudinal operation was achieved for both of them.

A study on stabilization of phase-drift in a high-extinction guided-wave intensity modulator

As a result of the optical pulse generation during the bias control of the modulator, the DERs of 38 dB and 35 dB were achieved for the duty cycles of 0.0056% and 1%, respectively.