Fused Silica is one of the key materials for 193 nm and 248 nm lithography as well as Laser Fusion experiments
(355nm windows) and is used for laser optics, beam delivery system optics and stepper/scanner optics for different
wavelengths including excimer laser wavelengths 193 nm / 248 nm / 353nm. Rising energy densities per pulse and
higher repetition rates will lead to decreasing exposure times in the future. The radiation induced defect generation of
Lithosil® at wavelength 248 nm and 193 nm is well described [1,2]. The lifetime of Fused Silica at high fluence
irradiation at 193 nm and 248 nm is limited by compaction and microchannel generation . Short time tests well
established for characterization of laser radiation induced defect generation in Lithosil® at irradiation wavelengths 193
nm and 248 nm were transferred to 353 nm laser irradiation experiments. Within these short time tests initial and
radiation induced absorption as well as the measurement of laser induced fluorescence (LIF) are adequate methods to
characterize the material under laser irradiation. Transmission and LIF measurements before and after high energy
irradiation were performed to reveal the applicability of different grades of Lithosil® for 353 nm laser applications.
Transmission, absorption and laser induced fluorescence (LIF) measurements were performed to reveal the applicability
of different grade CaF2 for 248 nm laser applications. No emission from self-trapped excitions could be found in LIF
measurements after irradiation with 100k pulses for all grades. Therefore, three-photon excitation could be excluded up
to 1 J/cm2. Whereas emission at 420 nm and partially the double-peak at 313/333 nm could be found in LIF
measurements. UV-VIS difference spectra did not show any absorption bands after 248 nm irradiation of the samples.
Optical elements from CaF2 promise high life expectancy at 248 nm if a standard laser polish is used and hot spots are
Combined measurements of transmission T, absorption A and total scattering TS revealed the high accuracy of all applied measurement techniques by obtaining a sum T+A+TS+R = (100±0.3)% (R denotes the Fresnel reflection). In order to investigate CaF2 at high fluences, a variety of samples from high purity excimer grade to research grade was irradiated (80 ... 150 mJ/cm2, 2*106...7*106 pulses) and characterized before and after irradiation by total scattering, laser induced fluorescence (LIF) and transmission measurements. Total scattering mappings showed negligible and
measurable scattering in excimer grade and some research samples of minor purity, respectively. For the first time to our knowledge, laser induced fluorescence measurements revealed increasing (580nm, 740 nm) as well as decreasing (313 nm, 333 nm) emissions. The small increases of the linear absorption, obtained in all samples by transmission measurements, were used to distinguish high from minor quality material. For high quality samples the linear absorption change scales with NH3 (N: number of pulses), whereas for minor quality research samples a NH2-scaling was found.
Carbon monoxide distributions around igniting n-heptane droplets were determined using absorption measurements. The emission of a quantum cascade laser at 4.6 μm was shaped to a parallel laser beam using a lens. For detection, a plane through the droplet, perpendicular to the laser beam was imaged onto the focal plane array of a mid-infrared camera. For background suppression a long-pass filter was mounted in the detection ray path. To estimate the detection sensitivity of the set-up, CO absorption in a reference cell was measured. In addition, CO transmission spectra were calculated for
different temperatures based on HITRAN 2000 catalogue.
Concentration profiles of OH, O2 and NO as well as temperature fields in diffusion flames of a length of approx. 300 mm and 40 mm in diameter used for gas-phase synthesis of fused silica have been determined by Planar Laser Induced Fluorescence (PLIF). The measurements have been carried out using a tunable spectrally narrowed KrF laser, whose wavelengths could be switched pulse-to-pulse. The laser beam was shaped as a light sheet into the flame at a fixed position. The flame area under investigation was monitored by moving the burner mounted on a stepper motor. By adapted synchronization the laser induced fluorescence was continuously recorded over the height of the flame perpendicular to the laser light sheet with an intensified CCD camera (10 fps, 8 bit dynamic range, 768 x 576 pixels). By image processing the spatial offset between images was corrected and superposed images were averaged and analyzed. This method allows to investigate the flame by recording 2D-fluorescence images including an automatic correction of intensity inhomogeneities of the laser light sheet. Based on the excited radical or molecule the fluorescence images were used to determine concentration and temperature distributions to build up a 2D-map of the flame. The PLIF experiment was calibrated with precise determination of the temperature at one coordinate of the flame by Spontaneous Vibrational Raman Scattering (VRS) of N2. As a result temperatures up to 3200 K could be determined with an accuracy better than 3% and a spatial resolution better than 1 mm. Temperature variations in the flame at different gas flows of fuel and oxidizer could be monitored sensitively. Also, the influence of different carrier gases like N2, Ar and He on the temperature distribution was investigated. Fluctuations in gas flow caused by turbulence could be monitored as well.