Strong-field applications of mid-IR ultrafast pulses

As can be seen in the history of science, new light sources open new research fields. In this project, the applicant Dr. T. Kanai together with the Ultrafast Laser Group led by Prof. A. Baltuska [Photonics Institute, the Vienna University of Technology (TU Vienna)] proposes to investigate some of the extremely promising applications of intense ultrashort Mid-IR (MIR) pulses applied in the strong-field regime to atoms and molecules. The key aspect of the proposed research, enabling qualitatively different regimes in the atomic and molecular strong-field optics, is the unique combination of the long wavelength and high peak power of intense few-cycle optical parametric amplifier (OPA). The technology of such novel laser sources has been under development at the host institution, TU Vienna, for the past several years. The applicant is proposing an ambitious research program that aims to take advantage of the ability of the long-wavelength strong-field drivers to achieve enhanced ponderomotive acceleration and resonant coupling to optically active electrons and atoms. The explicit project objectives can be written in terms of Work Packages (WPs) as below: [WP1] Construction of the MIR OPA [WP2] Proof-of-principle demonstration of ultrafast spectroscopy with transient MIR photoabsorption [WP3] Photoelectron spectroscopy with the MIR pulses [WP4] Heterodyne Interferometry of High harmonic generation (HHG) by the MIR OPA using mixed gases In the proposal, the logics and motivations behind the above four WPs will be explained in a systematic manner.

The most significant result of the present project is that we proved the wavelength region of 5-10 micron is feasible as next generation lasers for the ultrafast science. In ultrafast science, whose aim is to understand ultrafast phenomena as a kind of movies with the state-of-the-art technology on lasers and spectroscopy, there is a research trend to use longer wavelength lasers than that of the conventional titanium-sapphire lasers at 0.8 micron. For example in 2012, the record nonlinearity (5000th order) and the highest energy x-ray pulses (1.6 keV) were achieved by a 3-4 micron laser developed in Vienna University of Technology but nobody cannot predict if this wavelength is the best one or not due to the lack of laser technology at this wavelength region. By our results, we proved the wavelength region of 5-10 micron is feasible as a next generation laser for the ultrafast science by developing a novel, highest power 5.3 micron laser with some applications to nonlinear physics. The proved design of the 5.3 micron laser is scalable in terms of pulse energy and also cost efficient and it has impact not only for science but also for industry, medical science, and so on. In fact, our laser is started to be recognized as one of the feasible next generation laser that supersede standard titanium-sapphire lasers and commercial companies including THALES Optronique have started project to commercialize it. In addition to the results above, we also succeeded in sophistication of the 3-4 micron lasers in Vienna University of Technology. The problems of the results in 2012 was in the laser's long pulse duration (80 fs) and low repetition rate (20 Hz). In Ref. [P4], we developed 22 fs (sub-two cycle) 2.5 mJ, 3.2 micron laser system based on a combination of the high power Yb:CaF2 multi-pass amplifiers and large core density gradient hollow core fiber. From these results, it is expected to increase the flux and photon energy of x-rays by using a high harmonic generation process. Possible applications and/or implications of the present results to the other field are enormous. Technologies of x-ray has been a fundamental tool of modern age, which can be applied to enormous things such as diagnostics to crystals, semiconductors, biological objects including human body known as roentgenogram. From the present results, the advantages of laser based x-ray generation are proved in many points. Also the wavelength region of the developed laser system is known as a spectroscopically important region called the fingerprint region and most of many body molecules has its absorption lines in this regions. The strong field physics in this region, however, has not been studied due to the lack of high power laser technology. The laser technology developed here will lead to the fertile unknown physics in this novel and unexplored parameter region.