Molecular lasers, operating both pulsed and continuous-wave (cw) in the infrared, typically have their output wavelength tuned by Littrow-mounted gratings. High efficiency is obtained by operating in the first order at diffraction angles >20°. This corresponds to λ/d ratios from 0.67 to 1.8 (where d is the groove spacing), which ensures that only the zero and first orders can diffract. The output will be polarized in the S-plane (i.e., with the electric vector perpendicular to the grooves) because the efficiency will be several times greater than in the P-plane (electric vector parallel to the grooves). Dispersion is a function of the tangent of the diffraction angle β and is chosen from medium (β approximately 20°) to very high (β >50°) as required. When viewing the product listing, note that high efficiency corresponds to diffraction angles that can be significantly greater than the groove or blaze angles. This is a consequence of the electromagnetic nature of diffraction from deep groove gratings. For maximum efficiency, any of these gratings can be supplied in the form of gold replicas.
Some molecular lasers operate at high power, capable of destroying gratings. In the case of pulsed lasers, extra thick replica films may be of help, but at maximum intensity levels only original gratings survive. In the case of cw lasers, replicas on metal substrates are superior to glass because of far greater thermal conductivity; in some cases it is advisable to supply the substrates with water cooling. Otherwise, ruled originals on metal substrates are advisable. In all cases, close attention to groove geometry maximizes reflection, minimizes absorption and leads to improved grating performance.
There are a number of masters available that are used to produce replicas with high S-plane efficiency for use with CO2, CO, HF, or DF lasers. For this type of application, we suggest you advise us of the following specifications: spectral region of interest, peak power, pulse duration and beam size.
