Energy-efficient method and system for processing target material using an amplified, wavelength-shifted pulse train

TL;DR: In this article, an energy-efficient method and system for processing target material such as microstructures in a microscopic region without causing undesirable changes in electrical and/or physical characteristics of material surrounding the target material is provided.

Abstract: An energy-efficient method and system for processing target material such as microstructures in a microscopic region without causing undesirable changes in electrical and/or physical characteristics of material surrounding the target material is provided. The system includes a controller for generating a processing control signal and a signal generator for generating a modulated drive waveform based on the processing control signal. The waveform has a sub-nanosecond rise time. The system also includes a gain-switched, pulsed semiconductor seed laser having a first wavelength for generating a laser pulse train at a repetition rate. The drive waveform pumps the laser so that each pulse of the pulse train has a predetermined shape. Further, the system includes a fiber amplifier subsystem for optically amplifying the pulse train to obtain an amplified pulse train without significantly changing the predetermined shape of the pulses. The amplified pulses have little distortion and have substantially the same relative temporal power distribution as the original pulse train from the laser. Each of the amplified pulses has a substantially square temporal power density distribution, a sharp rise time, a pulse duration and a fall time. The subsystem also includes a wavelength shifter in the form of an optical fiber for controllably shifting the first wavelength to a second, larger wavelength to obtain an amplified, wavelength-shifted, pulse train. The system further includes a beam delivery and focusing subsystem for delivering and focusing at least a portion of the amplified, wavelength-shifted, pulse train onto the target material. The rise time (less than about 1 ns) is fast enough to efficiently couple laser energy to the target material, the pulse duration (typically 2-10 ns) is sufficient to process the target material, the fall time (a few ns) is rapid enough to prevent the undesirable changes to the material, such as silicon, surrounding the target material and the second wavelength more efficiently couples laser energy to the target material than the first wavelength. The subsystem may also include a filter coupled to the optical fiber to narrow bandwidth of the amplified, wavelength-shifted, pulse train. The second wavelength may be at the absorption edge of silicon.