Plasma level (physics)
The plasma mirror is a structure for improving the pulse contrast of modern high-intensity lasers . With the help of such a structure, the intensified spontaneous emission and undesired prepulses can be reduced in their intensity.
Focused to a laser pulse at intensities of 10 16 W / cm 2 on a non-reflective glass surface , the prepulse and the rich amplified spontaneous emission ( English emission amplified spontaneous ASE) before the main pulse is not sufficient to a supercritical plasma to ignite. Due to the low reflectance of the dielectric surface (this is typically in the range of 0.2%), they are almost completely transmitted . The intensity of 10 16 W / cm 2 of the main pulse, on the other hand, is several orders of magnitude above the ionization threshold of glass, so that the rising edge of the pulse generates a supercritical plasma and the degree of reflection increases sharply to up to 80%. The supercritical plasma reflects the main pulse like a metallic mirror and separates the ASE and prepulse from the main pulse. The resulting improvement in contrast is greater the more the plasma reflects and the better the anti-reflective coating on the original surface. Plasma levels with anti-reflective substrates are currently used in most laser devices with powers in the 100 TW range in order to reduce the ASE, which is strongly generated in regenerative amplifiers . For many experiments in laser plasma physics, such as the generation of high harmonic radiation on solids , the use of a plasma mirror or another contrast enhancement method is essential.
literature
- Christian Rödel, plasma mirror for contrast enhancement of terawatt laser pulses for the generation of high harmonics on surfaces , diploma thesis, 2009.
- C. Thaury, F. Quere, J.-P. Geindre, A. Levy, T. Ceccotti, P. Monot, M. Bougeard, F. Reau, P. d / 'Oliveira, P. Audebert, R. Marjoribanks, Ph. Martin: Plasma mirrors for ultrahigh-intensity optics . In: Nat Phys . tape 3 , no. 6 , 2007, p. 424-429 , doi : 10.1038 / nphys595 .
- C. Thaury, F. Quere, H. George, JP Geindre, P. Monot, Ph. Martin: High-order harmonic generation from plasma mirrors . In: The European Physical Journal . No. 175 , 2009, p. 43-48 , doi : 10.1140 / epjst / e2009-01115-6 .