Yunpei Deng
Max Planck Institute of Quantum Optics
Monday, February 20, 2012
4:30 p.m.
Cardwell 102
State-of-the-art laser technology is on the verge of
providing synthesized waveforms at optical frequencies. Such flexibility in
shaping arbitrary light waveforms permits sculpting an electric force for
steering electrons in any desired fashion within atomic, molecular and solid
systems, on the electronic time scale. This has promising potential in pushing
the frontiers of attosecond physics and of coherent control schemes to
completely unexplored regions.
Optical parametric chirped-pulse
amplifier (OPCPA) systems can produce nearly single-cycle pulses at a mJ energy
level, or few-cycle pulses at a hundred mJ level. In my talk I will present the
details of a mid-IR OPCPA laser system that I developed in last few years at
MPQ. As I will show, this system has already demonstrated an output of 1.2-mJ,
1.5-cycle (10.3fs) pulses at 2.1µm central wavelength and at 3 kHz repetition
rate. Such source is the key to achieving HHG X-ray photons in the keV domain,
and is also important to a wide range of highly interesting applications, such
as the investigation of ultrafast structural dynamics and conformational changes
of relevant molecules in biology. An additional benefit of the IR carrier
wavelength is the increased duration of its optical cycle (e.g. 7 fs for 2.1 µm)
compared with a NIR pulse (e.g. 2.5 fs for 750 nm). The increased spacing
between successive half-cycles of the laser pulse provides a sufficient time
window to capture the full dynamics of an arbitrary sub-femtosecond relaxation
process, before the identical process is re-triggered by the next half-cycle of
the laser pulse. It is a powerful and unique source for coherent control,
ionization and dissociation experiments. In my future plans I will show how an
OPCPA system, which can be developed to deliver more than two-octave bandwidth
pulses, is capable of producing sinusoidal-like, square, sawtooth or any
arbitrary waveforms. Such laser pulses will open the door to many ultrafast
coherent control applications.