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Nearly 60 Years in the Making - Today's High Power Lasers

The first Ti:sapphire petawatt class laser facility J-KAREN, Japan (source: JAEA).

The first Ti:sapphire petawatt class laser facility J-KAREN, Japan (source: JAEA).

September 5, 2018 | Source: American Scientist, ://www.americanscientist.org, Todd Ditmire

This article marked the 50th anniversary of development of the laser in 1960 and details the development path from that first few hundred watt laser to today's ultrapowerful petawatt and exawatt laser systems. The invention of the laser nearly 60 years ago has led to the latest generation of devices, with power bursts thousands of times that of the nation’s entire electrical grid. Lasers are remarkable devices. Their ability to produce a sharp, bright beam of light of a well-defined color is something that amazes students to this day. It could be argued that, after the transistor, the laser has been the most significant technological invention since World War II.


Lasers now find widespread application in an incredibly diverse range of duties, including reading compact discs, printing paper, scanning bar codes, machining and welding, precision surgery, finding distances, enabling high-speed communications, guiding precision munitions and driving controlled nuclear fusion. This year marks the 50th anniversary of the demonstration of the first laser, a feat performed by Theodore Maiman in his laboratory at Hughes Aircraft Company in 1960. The 50-year history of laser development since this first demonstration has had numerous twists, including the 30-year patent battle that surrounded the laser’s invention. But one of the most fascinating subplots in the story of laser development since 1960 has been the astonishing increase in the power that lasers can deliver.

One often thinks of lasers as delivering a continuous beam of light in one color that is well collimated (meaning the photons in the beam remain parallel and don’t diverge from each other). This is indeed the case for the miniature lasers that read compact discs or the barcode scanners in supermarkets, but there is a large class of lasers that deliver light in short pulses. Because power is defined as energy delivered per unit of time, when the energy emerging from the laser in a pulse of light increases and the time duration of the pulse decreases, the instantaneous power during the pulse—described more accurately as “peak power”— increases. Pulsed lasers find application in lofty tasks, such as the production of controlled nuclear fusion and laser eye surgery, down to the mundane, such as cosmetic hair removal. In fact, the high powers possible with pulsed-laser light were apparent from the very earliest days of laser development. Even Maiman’s first laser was pulsed and likely had a peak power of a few hundred watts (about the same power used by an average toaster oven today).

The enormous increase in lasers’ peak power through the past 50 years has been mind boggling. The peak power attainable in a laser pulse has increased by roughly a factor of 1,000 every 10 years. This power increase is much like the increase in the density of solid-state electronics described by the famous Moore’s Law—the number of transistors in an integrated circuit doubles about every two years. But unlike Moore’s Law, which has resulted from continuous incremental improvements in chip-manufacturing technology, the increase in lasers’ peak power has been the result of a few major breakthroughs in laser technology.

The article continues on to discuss:

  • laser light amplification or pumping, gain materials and energy storage;
  • development of Q-switching and the master oscillator, power amplifier (MOPA) architecture;
  • development of mode locking and its use to create ultrapowerful terrawatt and gigawatt pulsed lasers;
  • the use of diffraction gratings to develop Chirped-Pulse Amplification (CPA) techniques to solve the issue of "small-scale self-focusing" and optical component size; and
  • finally, the development of petawatt and exawatt class laser systems.

 

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