High-order harmonic generation in laser-produced plasmas

The high-order harmonic generation was performed at the vacuum conditions (Fig. 7). Here we present our experimental arrangements for HHG in laser-produced plasmas. We used 800 nm, 60 fs laser pulses as the probe pulses, which were converted to the harmonics in the plasmas created on the surface of the thin film containing CuO NEs using 800 nm, 200 ps heating pulses. More details about the experimental setup of HHG in the LPP of thin films were reported in ref.³². The thin film target on the surfaces of glass substrate was prepared from CuO suspension using spin-coating machine at the normal conditions. The uncompressed picosecond heating pulses were used for ablation of CuO NEs. The ablated CuO NEs entered the interaction area with probe femtosecond pulses (800 nm, 30 fs, 1 kHz) after 70 ns delay time. The delay time between heating and probe pulses was adjusted using optical delay line. The position of the target was adjusted using the translating stage to achieve the maximal harmonic yield generated in LPP. The extreme ultraviolet spectrometer containing a cylindrical mirror and a 1200 grooves/mm flat field grating with variable line spacing allowed detecting the harmonic up to 71th order. The spectra of harmonics were recorded by a micro-channel plate with phosphor screen, and the harmonics were imaged by a CCD camera.

Experimental setup of HHG in LPP: PB; Probe beam, BBO; nonlinear crystal, HB; heating beam, LLP; laser-produced plasmas, TFT; thin film target, PB + HHG; probe beam and high harmonic generation converted from probe beam in laser-produced plasmas.