Two-photon absorption at 248 nm in ultraviolet window materials

Abstract

Two-photon-absorption coefficients are measured for fused silica, LiF, and the alkali earth halides BaF(2), SrF(2), CaF(2), and MgF(2), using 0.7-psec, 248-nm pulses with intensities in the range (0.5-30) x 10(10) W/cm (2) . The conse-quences of these measurements in the design of high-brightness excimer lasers are discussed.

Characterization of absorption and degradation on optical components for high-power excimer lasers

“…1). Agreement with the value reported for transmission measurements at 1 O times higher intensity [2] is reasonable, considering that for similar materials, published data for the ps-and sub-ps-range vary by aboutone order ofmagnitude [2,3]. The absorption increase was completely reversible: whenever a series of irradiations was repeated with the same parameters several hours later, the data matched precisely.…”

“…In all these cases, the band-gap is wider than twice the laser photon energy, making two-photon absorption impossible. Since thin samples (dz = 1-5mm) are investigated, the differential form of Beer's law may applied: in crystalline quartz (z-cut) at 248nm/ 150Hz dI=-aldz, (2) and from the measured absorptance A = -dill I = dz a the linear absorption coefficient a can be derived …”

“…Accordingly, wide band-gap (8-13eV) optical materials such as ftised silica or alkali halide crystals are employed to insure high transparency and low losses as well as damage resistance and durability. However, intensity dependent absorption occurs even in these media: with p5 and sub-ps lasers reaching pulse power densities of up to 140GW/cm2, instantaneous transmission losses of several 10% have been measured and attributed to multi-photon absorption [1, 2,3]. Additionally, color center formation has been observed in some fluoride crystals above 100GW/cm2 [2,3].…”

“…However, intensity dependent absorption occurs even in these media: with p5 and sub-ps lasers reaching pulse power densities of up to 140GW/cm2, instantaneous transmission losses of several 10% have been measured and attributed to multi-photon absorption [1, 2,3]. Additionally, color center formation has been observed in some fluoride crystals above 100GW/cm2 [2,3]. In the ns range, due to damage threshold energy densities of about 1 OJ/cm2 [4], intensities must not exceed several 100MW/cm2 and, consequently, multi-photon absorption remains too small to be adequately detected by transmission measurements.…”

<title>Ti:sapphire-based ultrafast pump-probe laser source in the violet and ultraviolet</title>

“…In addition to using these sources to seed large rare gas halide excimer amplifiers in the ultraviolet1'2, generation of wavelength tunable femtosecond laser sources in the UV and near-VUV region3 are practical for a number of applications including: subpicosecond UV kinetic spectroscop'5, laser generated target plasmas6, wide band gap semiconductors7, and insulator material dynamics. 8 For time resolved femtosecond pump-probe spectroscopy, often one relies on the absorption of a broadband probe continuum for the detection of a transient species spectral feature. Generally, the probe continuum is generated by an intense femtosecond source through a nonlinear process in a gas or condensed phase medium called supercontinuum generation.9 This paper describes a femtosecond pump-probe system useful for detection of photochemical UV transients.…”