Highest performance from four cycles - record levels for ultra-short infrared pulses

High intensity infrared pulses of 75 femtoseconds duration at a wavelength of 5 microns provides a new light source with a repetition rate of 1 kilohertz. To generate peak optical powers in the range of 8 gigawatts, a multi-stage optical-parametric amplifier is used in conjunction with a compact short-pulse laser system. The infrared source has numerous applications in ultra-short-time physics and is u.a. used in the generation of extremely short hard X-ray pulses.

Ultra-short light pulses are an important tool in basic research and have found their way into numerous optical technologies. The infrared spectral range at wavelengths greater than 1 μm (1 μm = 10-6 m = 1 millionth of a meter) plays a central role not only in optical communication systems; Also in the optical measuring and analysis technique and in imaging techniques light with wavelengths between about 1 and 300 microns is used. A special technical challenge are extremely short impulses, in which the light waves oscillate only a few times, in the limit only once. The generation of such "few-cycle" pulses requires close control of the phase of light waves and their propagation conditions. The generation of intense infrared pulses with few optical cycles, high intensity and stability is a central topic of modern laser research.

Fig. 1: Experimental arrangement of the three-stage parametric amplifier. The amplification medium is three non-linear ZnGeP2 crystals (ZGP I-III). The optical beam paths are shown in false colors.

In the journal Optics Letters, researchers from the Max Born Institute in Berlin and BAE Systems, Nashua, NH, USA, report on a new light source that delivers ultrashort infrared pulses with record parameters. The highly compact system is based on the concept of optical parametric amplification. Optical Parametric Chirped Pulse Amplification (OPCPA), in which a weak ultra-short infrared pulse is amplified by interaction with a shorter wavelength intensive pump pulse in a nonlinear crystal. In the new light source, pump pulses of about 10 ps duration with energies of up to 20 mJ at 2 μm wavelength drive a three-stage parametric amplifier. A novel light modulator is used to optimally compress the amplified pulses at a wavelength of 5 μm. The amplified pulses have an energy of approximately 1 mJ and a duration of 75 fs, which corresponds to a peak power of 8 GW within approximately 4 optical cycles of the light wave. The highly stable infrared pulses are available at a repetition rate of 1 kHz and have excellent optical beam parameters. The output power and repetition rate of the system are scalable and can be optimized for different applications.

Fig. 2: Time intensity envelope of the infrared pulses (blue) of 75 fs duration (~ 4 optical cycles) at a wavelength of 5 μm. Inset: Spectral and temporal resolved impulse structure from a FROG measurement (FROG: Frequency Resolved Optical Gating).

These results have been recognized by the Editor-in-Chief of the journal Optics Letters as outstanding and open up new applications in ultra-short-time physics, such as the investigation of (bio) molecular vibration dynamics, low-frequency excitations in solids or the generation of short-wave ultrashort pulses. The new infrared system is ggw. integrated as an optical driver in a laboratory source, which will produce hard X-ray pulses of about 100 fs duration with repetition rates in the kilohertz range.

Original publication

5 µm few-cycle pulses with multi-gigawatt peak power at a 1 kHz repetition rate

L. von Grafenstein, M. Bock, D. Ueberschaer, K. Zawilski, P. Schunemann, U. Griebner, T. Elsaesser

Optics Letters 42 (2017) 3796-3799