This group was one of the first to recognize the essential role of dispersion in femtosecond laser cavities, and to achieve intracavity pulse compression with prisms [W. Dietel, J.J. Fontaine and J.-C. Diels, Optics Lett. 8, 4-6 (1983)], leading to 60 fs pulses, the world record in the early 80's.
Methods of pulse stretching and compression are easily implemented with fs pulses using chirped mirrors, prisms and gratings. Chirped pulse amplification is used to reach PW peak powers in fs pulses. There is however a need for methods to generate and amplify pulses in the picosecond to nanosecond range. One method that we developed is to compress and amplify pulses by stimulated Brillouin scattering, leading to 170 ps pulses at 266 nm of 300 mJ [1, 2].
"X-wave" shape spectrum of conical emission from filament
We have pioneered the field of filamentation in air, starting in 1995 when we reported the first observation of UV filaments with femtosecond pulses [Xin Miao Zhao, Patrick Rambo, and Jean-Claude Diels. Filamentation of femtosecond UV pulses in air. In QELS, 1995, volume 16, page 178 (QThD2), Baltimore, MA, 1995. Optical Society of America.]. Both UV and IR filaments are created in our laboratory out of a beam waist, prepared in vacuum and launched into the atmosphere through an aerodynamic window.
Laser induced discharges are used to produce large currents with very short risetime and minimal time jitter. Our efforts have been directed to triggering and guiding discharges across a relatively large gap. The investigations on laser induced high voltage discharges started in the 1970s. The problem with large gap discharges is that the guiding mechanism is the air rarefaction which itself results from a shockwave generated by the filament. This low density channel of air is a preferential path for the discharge.
We have constructed a Velocity Map Imaging setup adapted to the study of filaments. The main objective is to measure the distribution of energy and momenta of the electrons and ions under the influence of the field of the filaments. The VMI setup has passed the initial necessary vacuum tests and vacuums of up to 10-10 torr have been achieved.
We have demonstrated better than 10 pm spectral resolution in remote spectroscopy of plumes generated by UV filaments on solid targets [J-C Diels. Projecting high power density at long distance for standoff spectroscopy. In SCIentific eXchange SCIX conference 2017, Laser induced breakdown spectroscopy, Reno, Nevada, 2017.]