Researchers have found a way to generate more powerful, more energy efficient and low-cost pulsed lasers. The new method, described in journal Optica, could improve the use of pulsed lasers in applications such as telecommunications, metrology, sensing and material processing.
A team of scientists from the University of Southampton in the UK were behind the development. First author of the paper, David Wu, won the 2014 Engineering and Physical Sciences Research Council (EPSRC) ICT Pioneers award for the research.
Applications that require optical pulses typically need waveforms of a specific repetition rate, pulse duration, and pulse shape. However, it is often challenging to design and manufacture a laser with these parameters. Even when a suitable solution exists, the size, complexity and ease of operation of the laser are further critical considerations.
The new technique works on a different principle to existing pulsed lasers. It relies upon the coherent combination of multiple semiconductor lasers, each operating continuous-wave at different defined wavelengths. Through the control of the amplitude and phase of each laser’s output, it is possible to produce complex pulsed optical waveforms with a huge degree of user flexibility. The key to making the approach work is to phase-lock the semiconductor lasers to an optical frequency comb, which ensures the individual lasers have well-defined mutual coherence.
‘As our new technique is based on a different approach to that currently used, it has several distinct features that are relevant in many applications,’ said Wu. ‘First, it is easily scalable – by combining a larger number of input lasers, shorter or more complicated-shape pulses and/or more power can be obtained. It can also generate pulses with a very low-level of noise (down to the quantum limit) and very high (greater than one THz) repetition frequencies.
‘It consists of miniature and low-cost semiconductor lasers that can be all integrated on the same chip, making our pulse generator potentially very compact, robust, energetically efficient, and low-cost,’ he added.
According to the researchers, the technique will benefit any field of optics where pulsed laser sources are used. ‘We also believe that the concept and phase-locking technology developed could be widely applicable with the broader optics/photonics community,’ commented Dr Radan Slavik, who led the research team.
Compensating for pulsed lasers: Greg Blackman looks at the optics for ultrashort pulsed lasers, including those planned for the Extreme Light Infrastructure Beamlines facility, expected to become operational at the end of 2017