OSA & AMO JOINT SEMINAR
"Scaling Mid-IR Driver Sources to Terawatt Peak Powers"
Dr. Andrius Baltuška
Vienna University of Technology
Femtosecond multimillijoule longwave (λ=3-8 microns) lasers, as a consequence of a λ2 scaling of the ponderomotive energy, are critical in the generation of coherent  and incoherent  secondary radiation in the X-ray and THz domains . Such high-energy driver pulses are also proving indispensable in femtosecond filamentation  because of the unique opportunity to initiate plasma-chemical reactions with hot electrons emitted through long-wave optical field ionization. Further scaling of such longwave few-cycle sources, eventually into the relativistic regime, would make it possible to exploit the wavelength scaling advantage for particle acceleration and enable replacement of single-shot dense targets by indestructible high-pressure gas targets.
The talk reviews the current status of the intense mid-IR laser research at TU Vienna aimed at solving the scalability challenges of secondary sources and their laser pump systems and summarizes the most significant proof-of-concept applications demonstrated on our mid-IR systems. The merits and drawbacks of different mid-IR generation schemes based on-- in the ascending order of pulse energy-- i) four-wave mixing in gases, ii) single- and multicolor femtosecond optical parametric amplification (OPA) in nonlinear crystals and iii) chirped-pulse OPA (OPCPA) will be compared. We identify the limits of the current laser technology of 1-micron pump lasers based on Nd and Yb doped materials, which enable broadband parametric amplification at wavelengths up to 4.2 microns using state-of-the-art KTA crystals , and of 2.1-micron sub-ps pump lasers based on Ho-doped crystals  that permit the shift of the mid-IR carrier wavelength into the 5-8 microns range. Employing the 1-micron-pumped OPCPA architecture upgraded to the energy level of tens of millijoules and combined with external nonlinear pulse compression, we were able to reach the pulse duration measuring below 3 optical cycles at the wavelength of 4 microns, yielding driver pulses with the peak power of 0.7 TW and the pulse energy above 20 mJ at a 20-Hz repetition rate. With the advent of such high-peak-power sources, it has finally become possible to attain powers above the critical power of self-focusing in air at normal pressure, leading to the generation of mid-IR femtosecond filaments in the ambient atmosphere  (Fig. 1) and marking a significant step forward toward enabling several applications in atmospheric sensing in the chemically sensitive and eye-safe spectral range.
References:  T. Popmintchev, et al., "A new frontier for nonlinear optics: bright coherent kiloelectronvolt ultrafast x-rays generated on a tabletop", Science 336, 1287-1291 (2012);  J. Weisshaupt, et al., "High-brightness table-top hard X-ray source driven by sub-100- femtosecond mid-infrared pulses," Nature PhotonicsĚ 8, 927 - 930 (2014);  T. Balciunas, et al., "Optical and THz signatures of sub-cycle tunneling dynamicsĚ," Chem. Phys. 414, 92-99 (2012);  D. Kartashov, et al., "Mid-infrared laser filamentation in molecular gases", Opt. Lett. 38, 3194-3197 (2013);  G. Andriukaitis, et al.,"90-GW Peak-Power Few-Cycle Mid-IR Pulses from an Optical Parametric AmplifierĚ," Opt. Lett. 36, 2755 (2011);  P. Malevich, et al., "High energy and average power femtosecond laser for driving mid-infrared optical parametric amplifiers", Opt. Lett. 38, 2746-2749 (2013); and,  A. V. Mitrofanov, et al., "Mid-infrared laser filaments in the atmosphere," Scientific Reports 5, 8368 (2015).
Friday, March 6, 2015
IQSE 578, 11:30 a.m.
Mitchell Physics Building
OSA Student Chapter
Institute for Quantum Science and Engineering
Texas A&M University
Host: Dr. Aleksei Zheltikov
THE INSTITUTE FOR QUANTUM
SCIENCE AND ENGINEERING