Arbitrarily-shaped bursts of picosecond pulses from a fiber laser source for high-throughput applications

Abstract

Increasing the ablation efficiency of picosecond laser sources can be performed by bunching pulses in bursts 1 and benefit from heat accumulation effects 2-5 in the target. Pulsed fiber lasers are well suited for such a regime of operation, as the single pulse energy in a fiber is limited by the onset of nonlinear effects (SPM, SRS). Increasing the number of pulses to form a burst of pulses allows for average power scaling of picosecond fiber lasers. We are presenting in this paper a high-power fiber laser emitting arbitrarily-shaped bursts of picosecond pulses at 20 W of average output power. Burst duration can be varied from 2.5 ns to 80 ns. The burst repetition rate is externally triggered and can be varied from 100 kHz to 1 MHz. The single pulse duration is 60 ps and the repetition rate within a burst is 1.8 GHz. The output beam is linearly polarized (PER > 20 dB) and its M 2 value is smaller than 1.15. The laser source has a tunable central wavelength around 1064 nm and a spectral linewidth compatible with frequency conversion. Conversion efficiency higher than 60% has been obtained at 10 W of 1064-nm output power.

35/250 ytterbium-doped LMA polarization-maintaining fiber for high average and high peak power amplifiers

“…The drive current of the laser diode was first modulated with a digital waveform generator circuit. Ultrashort pulses were produced subsequently using an external phase modulator and a fiber Bragg grating to select only the blueish part of the frequency-modulated signal [6]. Thereafter optical pumping of all three amplifier stages was realized using wavelength-stabilized 976-nm laser diodes.…”

Potential of sub-microsecond laser pulse shaping for controlling microcavitation in selective retinal therapies

“…Also shown in the inset: comparison of the amplitude profiles in the nanosecond (black curve) and PB (red curve) laser operating modes for a given energy and pulse format (reprinted with permission from ref. 57). The durations employed for each pulse format and laser operating mode can be found in Table 1.…”

“…Figure 1 compares nanosecond and PB modes for a given pulse format in terms of the emitted peak power for the same total energy. Typically, the peak power is 4 − 5 times higher in the PB mode [57], compared to the nanosecond mode. By comparing experiments in both the nanosecond and the PB mode observations about the impact of the peak power and the effect of stress confinement on the cavitation threshold and on the bubble dynamics are extracted.…”

“…The concept of pulse duration gives limited information about rates of laser energy deposition in tissues, such rates being actually determined by the pulse amplitude profile or shape. The recent advent of nanosecond and picosecond fiber lasers with flexible pulse formats [52][53][54][55][56][57] opens up new opportunities for improving control and precision in laser treatments involving microcavitation. Pulse shape tailoring can be used to finely adjust the rate of energy coupling in tissues and can, in principle, be tuned to generate ideal temperature fields allowing for a precise control of both heat diffusion and the kinetics of vaporization, thereby optimizing thermomechanical confinement.…”

Genetic algorithm based optimization of pulse profile for MOPA based high power fiber lasers

“…Master Oscillator Power-Amplifier (MOPA) fiber laser has received much attention as the laser source for laser marking process due to its large tunabilty of pulse duration (from 10ns to 1ms) and repetition rate (100Hz to 500kHz), high peak power (larger than 10kW) and extraordinary heat dissipating capability [1][2][3][4]. Faster repetition rates and greater control over pulse energy offers the advantage of both faster and finer processing and a far wider processing range.…”