Process Raman is a unique application space with a specific set of challenging performance requirements. In general, it almost always uses a fiber coupled multi-mode laser source because process environments are often dangerous areas where customers are concerned about Ingress Protection and Explosion.
Equipment often needs to be designed to be explosion proof, waterproof, and dust proof. For this reason, process Raman teams frequently situate the laser and spectrometer in control-rooms connected to the Raman probe by long lengths of optical fiber (rather than mounting the equipment onto witness plates inside the processing facility).
In addition to the need for fiber coupled delivery, the lasers used for these applications need high levels of both power and wavelength stability. Since process controls depend upon measuring process changes, it is important that the laser change as little as possible so that small perturbations in the processing environment can be monitored.
The new ultra-stable Digital U-Type and M-type models are a great fit here since the power can be adjusted by both changing the current level AND by simultaneously applying a Pulse Width Modulation (PWM) sequence to decrease the average power. This module can be utilized in either Automatic Current Control (ACC) or Automatic Power Control (APC). When using in APC mode it is imperative to avoid spurious back reflections from the target sample as this can cause instability in the power control loop.