Tabletop OPA generates 10 TW

A new optical parametric amplifier that’s extremely efficient and small enough to fit on a desktop generates light pulses of more than 10 TW.

The amplifier, constructed by a team from the Laser Centre of the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) and the Faculty of Physics of Warsaw University, represents an important step toward construction of compact, portable, relatively low-cost high-power laser devices that could revolutionize cancer treatments, the researchers say.

“Theoretically, the efficiency of parametric amplifiers can reach over 50 percent,” said Dr. Yuriy Stepanenko of IPC PAS, who led the construction of the amplifier. “In practice, the best amplifiers of this type are operated at an efficiency of about 30 percent. We have reached this level already now, and what’s more, in a really compact device.”

Most lasers generating ultrashort pulses amplify light using sapphire crystals doped with titanium ions. An external laser pumps energy into the crystal, and a fraction of the energy is subsequently taken over by an amplified laser beam. The method has numerous disadvantages, one being that the crystals warm up strongly, leading to adverse distortions of the cross section of the laser beam. As a result, the crystals must cool down virtually after each laser shot.

Nonlinear optical effects can be used to construct a different type of amplifier. These parametric amplifiers effectively transfer energy directly from the pumping laser beam to the beam being amplified. As the input energy is not stored anywhere, there are no adverse thermal effects, and the amplified pulses have excellent parameters.

Parametric amplifiers can amplify light by hundreds of millions of times on an optical path of only a few centimeters. That’s also why they are very small in size, especially compared with standard high-power optics.

The new amplifier, which takes up only half of a typical desktop, will be used to construct an x-ray source and to generate experimentally protons and secondary neutrons, the researchers say.

One long-term objective of parametric amplifier research is to generate laser pulses with power of 200 TW and higher. Such powerful light pulses could accelerate protons to energies useful in medical treatments, such as selectively killing cancer cells. Existing techniques for proton acceleration require construction of huge, expensive accelerators; high-power lasers would increase the availability of state-of-the-art proton therapies while simultaneously reducing cancer treatment costs, the researchers say.

The next steps are to boost the amplifier’s efficiency and to increase the power of laser pulses, Stepanenko said.