05 October 2017
A novel light source provides infrared pulses of 75 femtoseconds duration at a wavelength of 5 micrometer and a repetition rate of 1 kilohertz. A multi-stage optical parametric amplifier in combination with a compact short-pulse laser system serves for the generation of very high peak powers in the range of 8 gigawatts. This infrared source holds potential for a broad range of applications in ultrafast science and, in particular, for generating extremely short hard x-ray pulses.
Ultrashort optical pulses are an important tool of basic reserach and a key ingredient of numerous optical technologies. The infrared spectral range at wavelengths beyond 1 µm (1 µm = 10-6 m = one millionth of a meter) is not only relevant in fiber-based optical communications; light with wavelengths between 1 and 300 µm is also used in optical analytics, sensors, and imaging technologies. A particular challenge consists in the generation of extremely short pulses in which the optical waves oscillate a few times only, in the limiting case only once. The generation of such "few-cycle" pulses requires a precise control of the optical phases and the propagation conditions. Sources providing intense few-cycle infrared pulses of high intensity and stability are a central topic of current laser research.
In the journal Optics Letters, a team of scientists from the Max Born Institute in Berlin and the company BAE Systems, Nashua, NH, USA, reports a new light source providing infrared pulses with record parameters. The highly compact system is based on the method of optical parametric chirped pulse amplification (OPCPA) in which a weak ultrashort infrared pulse is amplified in a nonlinear crystal by interaction with an intense pump pulse of a shorter wavelength. In the present light source, pump pulses of a 2 µm wavelength and a 10 ps duration drive a three-stage parametric amplifier with a pump energy of up to 20 mJ. A novel light modulator is implemented for optimal compression of the amplified pulses centered at a wavelength of 5 µm. The amplified pulses display a pulse energy of ~1 mJ and a duration of 75 fs, corresponding to a peak power of some 8 GW within the 4 optical cycles. The highly stable infrared pulses are generated with a 1 kHz repetition rate and show excellent optical beam parameters. The output power and repetition rate are scalable and can be optimized for different applications.
Temporal intensity envelope of the infrared pulses (blue) of a 75 fs duration (~4 optical cycles) at a central wavelength of 5 µm. Inset: Spectrally and temporally resolved pulse structure from a FROG measurement (FROG: Frequency Resolved Optical Gating).
Source: MBI Berlin
The results were recognized as an "Editor’s pick" by Optics Letters and hold strong potential for opening new areas of application in ultrafast science, e.g., for studying (bio)molecular vibrational dynamics, low-frequency excitations in solids, and/or generating ultrashort pulses at short wavelengths. The new infrared source is presently being implemented in a laboratory source for hard x-ray pulses with a 100 fs duration and kilohertz repetition rates.