By: Shinobu Tamaoki

Sumitomo Electric Inc.

Pulse fiber lasers (PFL) have become widely popular for micro-machining applications due to their many benefits, such as the high beam quality, compactness, high wall-plug efficiency, and reliability. MOPA (Master Oscillator Power Amplifier) architectures, which provide temporal pulse shape control, are particularly interesting.

Sumitomo Electric’s MOPA PFL is configured to control the pulse width from 0.2ns to 20ns (full width at half peak power) as the repetition frequency is varied up to 1000kHz.  It includes a specially designed pulse generator that directly modulates the 1064nm seed diode laser. This seed pulse is amplified by Yb-doped fiber modules to achieve an average output power of 15W.  At a pulse width of 1ns, the peak power is greater than 20kW at 100kHz and the laser provides a pulse energy of 170mJ.  At a pulse width of 0.2ns, the peak power is 85kW at 150kHz, and pulse energy is 30mJ.  A termination module containing a collimator and isolator is normally attached at the end of the delivery fiber.  The output beam diameter is set to about 1.0mm.  M2 is typically measured to be less than 1.3.  This special PFL may also be configured to provide 1ms pulse width, burst pulse operation, and temporally shaped pulse.  Optionally, optical elements may be added to deliver a rectangular spatial beam profile.  A 532 nm version is now being developed that has demonstrated an average power of 5W, with a peak power of 7kW, and pulse energy of 16mJ at 300kHz.

By providing flexible pulse durations over a wide range, this laser provides an ability to optimize process parameters and achieve both speed and quality. We have focused on thin film solar applications. Using this laser, P1 lines have been successfully scribed on three kinds of coated glass for PV cells, namely amorphous-Si, CdTe, and CI(G)S (CuInGaSe) samples.  For the ablation of TCO films on a-Si and CdTe samples, a pulse width of 20ns is preferable, and a scan speed of 2500mm/s has been demonstrated.  As for the ablation of Mo-layer for CI(G)S, a pulse width of 0.5ns is preferable, and a scan speed of 5000mm/s has been demonstrated.  Both P1 scribing applications have been achieved using a single laser with temporal pulse control.  We believe that this new PFL will be useful to reduce the capital expenditure and the production costs for manufacturing thin film solar panels.  Moreover, temporal pulse control allows process optimization for the next-generation PV cells with novel designs and/or novel materials in the near future.