Optical extraction efficiency in gas-flow lasers

It is shown that the celebrated Rigrod model [J. Appl. Phys. 34, 2602 (1963)] is inadequate for calculating the output power of gas-f low lasers in an important range of parameters in which the quenching of the excited species is slow and the optical extraction eff iciency is high. For two-level systems very simple analytical formulas for the output power are obtained that should be used instead of the Rigrod model. The formulas are given for Fabry-Perot, stable, and unstable resonators. Both the saturation parameter and the extraction efficiency differ from those appearing in the Rigrod model. Applications of the formulas to systems with more complex kinetic schemes are also indicated.

Laser photobleaching leads to a fluorescence grade adenosine deaminase

The enzyme adenosine deaminase (adenosine aminohydrolase EC 3.5.4.4) from calf intestinal mucosa is commercially available at high purity grade yet, at the sensitivity at which fluorescence studies may be undertaken, a nonpeptidic fluorescence is detectable at lambda exmax = 350 nm and lambda emmax = 420 nm. A sevenfold decrease of this nonpeptidic fluorescence was obtained upon irradiation by the third harmonic (355 nm) of a Nd:YAG laser for 16 min, at 5 mJ/pulse, with a pulse width of 6 ns at a repetition rate of 10 Hz. The decline of fluorescence was accompanied by a negligible loss of enzymatic activity. Moreover, the integrity of the protein was ascertained by (i) its fluorescence (lambda exmax = 305 nm, lambda emmax = 335 nm) and lifetime distribution and (ii) its kinetics in the presence of the substrate adenosine and two inhibitors, all of which remained essentially unaltered. Laser photobleaching is a simple way to achieve a fluorescence grade adenosine deaminase.