page_title: Resonant high harmonic generation from laser ablated plasma plumes
section_title: Three-Step Model
hierarchical_section_title: Resonant high harmonic generation from laser ablated plasma plumes / Three-Step Model
caption_attribution_description: English: Three Step Model for HHG.
context_page_description: High Harmonic Generation is a non-perturbative and extremely nonlinear optical process taking place when a highly intense ultrashort laser pulse undergoes an interaction with a nonlinear media. A typical high order harmonic spectra contains frequency combs separated by twice the laser frequency. HHG is an excellent table top source of highly coherent extreme ultraviolet and soft X-ray laser pulses.
context_section_description: HHG process can be very easily as well as intuitively explained by a simple three-step model originally proposed by Paul Corkum in 1993.
  Step 1: The outermost electron undergoes tunnel ionization upon interaction with the ultrashort laser pulse.
  Step 2: This tunnel ionized electron undergoes acceleration under the effect of laser pulse electric field.
  Step 3: When the electric field the ultrashort laser pulse undergoes the reversal of direction, this accelerated electron returns back and recombines radiatively with the parent ion emitting high harmonics.
  In Corkum's three-step model, the electron is treated as a free particle having no effect of the coulomb potential.
  Since the tunnel ionization and recombination process is happening twice in every cycle of the excitation laser pulse, the HHG process has the capability to generate the attosecond bursts of radiation by using femtosecond laser pulses as a source of excitation.
caption: Three step model of high-harmonic generation
exif: {}