ИСТИНА

The use of spatially modulated targets in laser-plasma experiments leads to an anomalous increase of the laser energy input and to a growth of X-ray radiation efficiency, spatial selection of high harmonics and modification of their spectrum. Combining methods of plasmonics and mid-infrared (IR) photonics provides the enhanced efficiency of various nonlinear optical phenomena due to the joint action of the wavelength-scaling laws of the electron ponderomotive energy and the lifetime of surface plasmon. In our experiments, laser radiation with λ0 = 3.9 µm and τ0 ≈ 100 fs was introduced into a vacuum chamber and focused by a parabolic mirror on the surface of aluminium difftaction grating, located at a plasmon resonance angle of incidence. The intensity of the focused laser radiation reached I0 ≈ 10^17 W/cm^2. The 2f-2f image of the high-harmonic radiation source was transferred by mirrors and lenses to the input of the spectrometer. The interaction of mid-IR laser pulses with the diffraction grating surface results in the generation of well-resolved, high-contrast harmonics in a wide range of angles exceeding the specular reflection angle. A pronounced sensitivity of the harmonic signal to the initial chirp of laser pulses has been observed.