Image Number 10 for United States Patent #8036252.
A mid-infrared system for optical probing is disclosed that comprises a mid-infrared fiber laser based on cascaded Raman wavelength shifting, a sample volume, and a detector or detection system. The cascaded Raman wavelength shifting process in optical fibers involves the emission of a plurality of optical phonons for at least some of the pump photonics involved in the process. As one example, using the cascaded Raman wavelength shifting process a pump laser wavelength between 1 and 2 .mu.m can be shifted down to between 2.5 to 10 .mu.m. In one embodiment, the mid-infrared fiber laser comprises a pump laser with a wavelength between 1 and 2 .mu.m, one or more stages of cascaded Raman oscillators implemented in fused silica fiber, and one or more stages of cascaded Raman oscillators implemented in mid-infrared fiber that transmits beyond 2 .mu.m. Examples of mid-infrared fibers include chalcogenides, fluorides and tellurite fibers. The output wavelength from the mid-infrared fiber laser is at an exemplary wavelength longer than 2.5 .mu.m. The mid-infrared optical probing system can be used in applications such as semiconductor process control, combustion monitoring for engines, and defense or homeland security applications such as chemical sensing and infrared counter-measures.