FEATURE ULTRAFAST AMPLIFIERS ➤
Arrigoni, director of strategic marketing, scientific segment at Coherent. ‘The downtime cost is something like $30-40k an hour,’ he said. Coherent is employing an industrial testing
process of highly accelerated life testing (HALT) and highly accelerated stress screening (HASS) testing in its more recent ultrafast products. ‘This hasn’t been the case in the high-performance ultrafast laser market to any great degree,’ commented Coherent’s director of marketing for research laser systems, Steve Butcher. ‘We’ve been deploying that testing both in the design and production phases to screen out potential problems with the systems before they get to the field.’ Coherent’s Vitara femtosecond oscillator, used at
Stanford LCLS and Elettra Sincrotrone, is HALT/ HASS-tested, as is the company’s Astrella laser amplifier, which produces 6mJ pulse energy at 1kHz and sub-35fs. ‘The focus is on reliability and lifetime; it is a one-box amplifier, including the oscillator, amplifier and laser,’ commented Butcher, referring to the Astrella. ‘The laser is water cooled, keeping complexity down. We want to offer a high- performance, reliable laser at an attractive price. ‘Scientists are interested in minimising the cost of acquiring data,’ he continued. ‘Because Coherent designs and manufactures Astrella using HALT/ HASS techniques, the reliability will be there and we’re able to offer attractive extended warranties of up to five years, which have not been available in the past. That means a lot for customers, especially in the US, where scientists might find it difficult to get funds for maintenance.’ The HALT and HASS tests are designed to weed out all the opto-mechanical weaknesses – mounts that are not rigid or might break, sub-micron scale misalignment of parts, as well as how the components shift with changing temperature. ‘Scientists want an
amplifier that behaves like a black box,’ said Arrigoni. ‘They don’t want to have to become specialists in laser
Scheme of the regenerative amplifier built by Trumpf Scientific Lasers The damage
threshold intensities of dielectric materials are much higher for picosecond pulse durations
systems to run their experiments. The reliability and the reproducibility of the performance day after day have become as important as the advanced performance. This is why we see the HALT/HASS approach is of paramount importance.’
Attosecond science At the extreme end of ultrafast science are attosecond lasers, systems delivering pulses of light so short they can image electrons moving or molecular bonds forming. In June, Trumpf Scientific Lasers will supply its first customer with a parametric amplifier that has pulses a few
26 ELECTRO OPTICS l APRIL 2014
femtoseconds in duration, and which is a suitable beam source for generating attosecond pulses. The laser is an optical parametric chirped pulse amplifier (OPCPA) offering high pulse energies, high repetition rate and pulses less than 5fs, known as few-cycle laser pulses. The branch of Trumpf uses standard Ti:sapphire oscillators and amplifies them using an in-house developed pump source based on Trumpf thin disk picosecond technology especially tailored for pumping OPCPAs. Dr Thomas Metzger, head of technology at Trumpf Scientific Lasers, explained that when a
Ti:sapphire broadband seed pulse is overlapped in a nonlinear crystal with a pump laser in space and time, then the seed can be amplified to multi- millijoule pulse energies at kilohertz repetition rates. This is an order of magnitude higher than standard Ti:sapphire amplifier technology, he said. Metzger said the TruMicro series 5000 picosecond laser is the ideal pump source for parametric amplification. He said the short pump pulses equate to high intensities when the light is focused into a nonlinear crystal. Therefore, with picosecond pulses, 107
or 108 amplification can be achieved in a crystal a few millimetres in size.
The damage threshold intensities of dielectric materials, such as the nonlinear crystals used in OPAs, are much higher for picosecond pulse durations. ‘It’s a complex process. It’s not visible at first glance why we use picosecond lasers for pumping OPAs. It all boils down to the increased damage threshold of this nonlinear crystal for picosecond pulses,’ said Metzger. Trumpf is able to use thin nonlinear crystals due to the high damage threshold and still able to achieve large amplification values while maintaining a broad bandwidth.
‘The technology can produce very short pulses of 5fs and peak powers of terawatt-level,’ said Metzger. ‘This can be achieved fairly simply, with one or two nonlinear crystals. Other terawatt lasers based on Ti:sapphire are huge; they probably need an entire laser laboratory. We can do this now in a compact parametric amplifier on an optical table.’ Trumpf Scientific Lasers is working on
reaching higher pulse energies and also at taking this parametric amplifier technology out of the laboratory and using it to build a reliable tool for scientists. ‘The goal is to equip the attosecond laser community with reliable lasers, for areas like attosecond spectroscopy or for observing how electrons move under real-time conditions,’ Metzger said. ‘There is a market for attosecond lasers,’ he concluded. ‘The attosecond community is very active right now.’ l
@electrooptics |
www.electrooptics.com
Trumpf
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