Warsaw, Poland--Gain crystals in conventional high-peak-power femtosecond lasers often heat up enough to distort the laser beam, reducing beam quality. An alternative approach is provided by optical parametric amplifiers that exploit nonlinear optical effects. A laser with such an amplifier is being developed at the Laser Centre in the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) and the Faculty of Physics of the Warsaw University (FPWU).
The multipass noncollinear optical parametric chirped-pulse amplifier (NOPCPA) technology has been in development for several years at the Laser Centre by a group headed by Czeslaw Radzewicz. The technique produces an efficient energy transfer directly from the pump-laser beam to the beam being amplified. Combined with numerical modeling, theoretical tools developed by the researchers allow precise optimization of the parameters for both beams and the amplifier. These issues are nontrivial, as field intensity distributions are inhomogeneous in time and space; in addition, the pulse being amplified has a chirp (a time-dependent frequency).
No thermal beam distortion
Because no energy is being accumulated in a parametric amplifier, there are no damaging thermal effects, and the amplified pulses have excellent parameters. A NOPCPA amplifier is also small: a length of several centimeters is enough to reach an amplification factor in the hundreds of millions. Theoretical efficiency of such an amplifier is approximately 60% but is difficult to achieve; so far the best laser amplifier of this type reaches an efficiency of less than 30%. "Our minimum plan is to reach an efficiency of 40%; we will try, however, to overcome a barrier of 50%," says researcher Pawel Wnuk.
The first 10 TW pulses, with duration of about 12 fs, are expected next year. "We hope that already the present version of the parametric amplifier will allow us to generate over 100 TW pulses," says Radzewicz. Calculations indicate that 500 TW laser pulses could be used to accelerate protons to energies that enable them to be used for medical therapy, including anticancer treatment. Currently, lasers with high-enough power for this can be found only in a few research centers worldwide. Yuriy Stepanenko, another researcher, believes the new NOPCPA-based source can be made small enough to be portable.
Two demonstration setups are to be constructed. The first will be used to produce x-ray sources with micrometric dimensions--useful for x-ray microscopy and nondestructive testing of structural materials. The second demonstrator will be a light detection and ranging (LIDAR) device for measurements of atmospheric pollution.
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