Deconvolution of surface and direct metastable- state blackbody emission in Ti:sapphire laser materials using boxcar time-domain photothermal radiometry

Abstract

Single-gate boxcar-integrator time-domain photothermal radiometry (PTR) is proposed as a noncontact remote technique with a high signal-to-noise ratio that can evaluate the optical quality of the surface in a solid-state laser-gain medium such as Ti:sapphire. It was found that immediately after the boxcar-averaged laser-pulse cutoff, the PTR signal is dominated by the laser metastable-level transition lifetime. A PTR theoretical model was formulated to account for this effect and to deconvolute its contribution to the signal from surface absorption of the laser radiation. With the theoretical model, the surface contribution to experimental boxcar PTR signals was deconvoluted and the surface quality was quantified in terms of the surface nonradiative energy generation rate, as the percentage of the input optical power that is converted to heat.

Quantitative dental measurements by use of simultaneous frequency-domain laser infrared photothermal radiometry and luminescence

“…where ⌳ denotes wavelength, ⌳ 1 and ⌳ 2 are the limits of the spectral bandwidth of the infrared detector, and W͑⌳͒ is a wavelength-dependent coefficient involving the Planck distribution function and the spectral response of the detector. 16 C is a constant involving both instrumental factors ͑e.g., the system transfer function͒, and the grouping of physical terms 4εT 0 3 for small thermal-wave amplitudes ͉T max ͉ Ͻ Ͻ T 0 . T 0 is the ambient temperature, is the Stefan-Boltzmann constant ͓ ϭ 5.6703 ϫ 10 Ϫ8 W͞m 2 K 4 ͔, and ⑀ is the emissivity of the turbid medium.…”

“…18,19 Majaron et al 17 range, an essentially surface localization of the IR emission contribution is expected, compared with the much longer absorption length 1͞ ␣ of the laser exciting radiation. Furthermore, it is expected 16 that the spectral variation of eff can be much reduced at shallow depths, and thus the error committed by use of the approximate Eq. ͑21͒ may be much less than 30%.…”

Diagnostics of nonradiative defects in the bulk and surface of Brewster-cut Ti:sapphire laser materials using photothermal radiometry

“…As discussed in more detail elsewhere [17], [18], the PTR technique has the ability to monitor nonradiative processes occurring in the bulk and surface simultaneously. By detecting the IR emission from a laser material at very short times after pulse cutoff, one can characterize the laser material surface.…”

“…Since this approach calls for time-domain detection, a theoretical model of the timedependent IR emission from a crystal in response to a laser pulse was developed. The details of this treatment are given elsewhere [17], [18]. However, the final expressions for the early-time and late-time IR emission are shown below.…”

“…denotes the lifetime of the upper laser level 2 whereas represents the lifetime of the laser transition. We can then write the equation governing early-time IR radiation emission from a laser crystal as [17] (1)…”