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Time-resolved-photography and transient absorption spectroscopy of excited dielectrics by infrared ultrashort laser radiation

: Horn, A.; Kreutz, E.W.; Poprawe, R.

Brandt, M.:
PICALO 2004, 1st Pacific International Conference on Applications of Lasers and Optics. Peer reviewed conference proceedings. CD-ROM : April 19 - 21, 2004, Grand Hyatt Melbourne, Melbourne, Australia; sessions featuring Laser Materials Processing Conference, micro, nano and ultrafast fabrication
Orlando, Fla.: LIA, 2004 (LIA publication 596)
ISBN: 0-912035-76-5
ISBN: 978-0-912035-76-5
Pacific International Conference on Applications of Lasers and Optics (PICALO) <1, 2004, Melbourne>
Laser Materials Processing Conference <2004, Melbourne>
Fraunhofer ILT ()

Compared to laser radiation in the nanosecond regime, glass is modified using femtosecond laser radiation without cracking. The modification of the matrix structure of glass (BK7 glass, fused silica and quartz) is investigated during and after irradiation with ultra short pulsed laser radiation (70 fs< t(ind p) < 3 ps) at the wavelength lambda = 810 nm. Glass is heated by femtosecond laser radiation within the irradiation zone for many nanoseconds.
The dynamics of absorption after excitation of fused silica and BK7 glass with femtosecond laser radiation is visualized by transient absorption spectroscopy. Focusing laser radiation with pulse durations in the picosecond time regime in Sapphire generates free electrons with relaxation by emission of radiation or by formation of defects. The temporal and spatial emission characteristics are observed by high-speed photography in the streak mode. The beam waist moves within the pulse duration towards the incident laser radiation by self-focusing and absorption by multiphoton processes. The dynamics of the long lasting stress formation is visualized by time-resolved Nomarski photography. The formation of a sound wave in fused silica and BK7 glass is observed and the mechanical stress, depending on the excitation pulse duration, is measured.