Absorption of subpicosecond ultraviolet laser pulses in high density plasma
The absorption of 250 fs KrF laser pulses incident on solid targets of aluminium, copper and gold has been measured for normal incidence as a function of laser intensity in the range of 1.0 E12 to E14 W/cm2 and as a function of polarisation and angle of incidence for the intensity range of 1.0 E14 to 2.5 x 1.0E15 W/cm2. As the intensity increases from 1.0E12 W/cm2 the reflectivity at normal incidence changes from the low-intensity mirror reflectivity value to values in the range of 0.5 - 0.61 at 1.0E14 W/cm2. For this intensity maximum absorption of 63-80% has been observed for p-polarised radiation at angles of incidence in the range of 54 - 57 , increasing with atomic number. The results are compared with the expected Fresnel reflectivity from a sharp vacuum-plasma interface with the refractive index given by the Drude model and also to numerical calculations of reflectivity for various scale length density profiles. Qualitative agreement is found with the Fresnel/Drude model and quantitative agreement is noted with the numerical calculations of absorption on a steep density profile with normalised collision frequencies, in the range of 0.13-0.15 at critical density and normalised density gradient scale lengths, in the range of 0.018-0.053 for a laser intensity of 1.0 E14 W/cm2. At 1.0 to 2.5 E15 W/cm2 a small amount of preplasma is present and maximum absorption of 64-76% has been observed for p-polarised radiation at angles of incidence in the range of 45 -50 .
Bibliographic Reference: Article: Applied Physics B, Vol. 50 (1990) pp. 79-99
Record Number: 199011152 / Last updated on: 1994-12-01
Original language: en
Available languages: en