High harmonic generation in plasma plumes is an interesting light source. Compared to gas harmonics there is a plethora of choice for target materials. Of particular interest are carbon targets and transition metals. In Carbon targets we have shown very high conversion efficiencies. From transition metal targets (for example indium, tin, and manganese) resonant HHG is possible. These sources can offer spectrally bright coherent light with potentially attosecond pulse durations.
Experimental setup for plasma plume HHG. A part of the uncompressed laser output is used as a pre-pulse to ablate the solid target material. After approx 30ns the few-cycle pulse is focussed into the underdense plasma plume to generate harmonics. The target is rotating to enable long term operation.
A selection of targets for plasma HHG.
Spatial coherence measurement of carbon ablation plume harmonics.
In case of resonances the 3-step model of high harmonic generation becomes a 4-step model. The electron is trapped in an autoionising state.
Relevant Publications:
Hutchison, Christopher, Rashid A. Ganeev, Tobias Witting, Felix Frank, William A. Okell, John W. G. Tisch, and Jon P. Marangos. “Stable Generation of High-Order Harmonics of Femtosecond Laser Radiation from Laser Produced Plasma Plumes at 1-kHz Pulse Repetition Rate.” Optics Letters 37, no. 11 (June 1, 2012): 2064–66. doi:10.1364/OL.37.002064. link
Ganeev, R., T. Witting, C. Hutchison, F. Frank, P. Redkin, W. Okell, D. Lei, et al. “Enhanced High-Order-Harmonic Generation in a Carbon Ablation Plume.” Physical Review A 85, no. 1 (January 2012): 3–6. doi:10.1103/PhysRevA.85.015807. link
Ganeev, R. A., C. Hutchison, T. Witting, F. Frank, W. A. Okell, A. Zaïr, S. Weber, et al. “High-Order Harmonic Generation in Graphite Plasma Plumes Using Ultrashort Laser Pulses: A Systematic Analysis of Harmonic Radiation and Plasma Conditions.” Journal of Physics B: Atomic, Molecular and Optical Physics 45, no. 16 (August 28, 2012): 165402. doi:10.1088/0953-4075/45/16/165402. link
Ganeev, R. A., T. Witting, C. Hutchison, F. Frank, M. Tudorovskaya, M. Lein, W. A. Okell, A. Zair, J. P. Marangos, and J. W. G. Tisch. “Isolated Sub-Fs XUV Pulse Generation in Mn Plasma Ablation.” Optics Express 20, no. 23 (November 5, 2012): 25239–48. doi:10.1364/OE.20.025239. link
Ganeev, R. A., Z. Abdelrahman, F. Frank, T. Witting, W. A. Okell, D. Fabris, C. Hutchison, J. P. Marangos, and J. W. G. Tisch. “Spatial Coherence Measurements of Non-Resonant and Resonant High Harmonics Generated in Laser Ablation Plumes.” Applied Physics Letters 104, no. 2 (January 17, 2014): 021122. doi:10.1063/1.4861161. link