Ultra-short radiation generation from Mid IR-THz range using plasma wakes and relativistic ionization fronts

In this talk we will discuss two different concepts for frequency downshifting and upshifting of an IR laser to cover the entire bandwidth from 1 to 300 $\mu $m using two different plasma techniques. Recently we have demonstrated a new scheme that utilizes frequency downshifting of a Ti-saphhire laser using a wake produced in a tailored plasma structure to generate multi-millijoule energy, single-cycle, long-wavelength IR pulses [1,2]. Extending this idea, sub-joule, single-cycle terahertz pulses can be generated by using a picosecond 10 $\mu $m CO$_{\mathrm{2}}$ driving laser. On the other hand, such a CO$_{\mathrm{2}}$ laser can be frequency upshifted by colliding it with an underdense but relativistic ionization front [3]. In this case the wavelength can be tuned from 1-10 $\mu $m by simply tuning the gas density. These plasma techniques seem extremely promising to covering the entire molecular fingerprint region. References: [1] Z. Nie, et. al., Nat. Photon. 12, 489-494 (2018). [2] Z. Nie, et. al., Nat. Comm. 11, 2787 (2020). [3] W. B.~Mori,~Phys.~Rev. A~44,~5118~(1991).