Laser Raman Spectrometer
Project Manager/Lead Engineer: George Malby
Lead Scientist: Peter Brewer

The proposed year 2002 Laser Raman Spectrometer (LRS) program is a continuing project to design, configure and field a Laser Raman Spectrometer for use by the MBARI science community in furtherance of their research efforts in the deep Ocean. Initially, the LRS will support the research initiatives of the Ocean Chemistry of the Greenhouse Gases Project. It is however a general purpose measurement tool for advanced ROV deployment allowing for the in situ molecular speciation of many types and forms of chemical and biological samples.

The year 2001 effort resulted in the design, test, fabrication and integration of a state-of-the-art LRS commercial instrument. The instrument was demonstrated to work well in its field configuration in the laboratory.  Laboratory testing of the LRS has shown that the high pressure tolerant fiber optic interconnecting cables exhibit 5 dB more optical loss than their conventional counterparts, resulting in an in-water system level configuration reduction in detection sensitivity of 10 dB. These losses appear to be due to the pressure-tolerant in-line connectors. Additional work to obtain lower loss pressure tolerant fiber optic cables, connectors and penetrators is required.

The spot size of the probing laser beam is on the order of a fraction of a square millimeter (when using a 2.75 inch focal length set of relay optics) and J. Freeman at Washington University (WU) has determined that the depth of field for maximum sensitivity is on the order of one millimeter. Thus in order for the LRS to be truly usable in deep water research applications, a "through the lens" visualization capability and a precision XYZ positioning capability are required. As the LRS methods utilization and development tasks in science proceed, it is anticipated that new optical probe head requirements (different focal lengths and spot sizes) and different sampling techniques (a sampling configuration for determining the molecular composition of pore waters in sediments for example) will need to be designed, fabricated and integrated with the basic LRS.

Obtaining spectral data quality control information is an important part of the evolution of the LRS instrument capabilities if the resulting science data is to be ported/shared between MBARI and other scientific institutions. In situ instrument temperature and humidity measurements will be appended to the measured spectral data obtained from the LRS. Our WU collaborators have suggested that a diamond (insensitive to temperature and pressure) local standard (Zheng et al., 2001) be incorporated in the LRS optical head sensing path so that every spectrogram could have an internal standard for comparison. We will evaluate the feasibility and desirability of incorporating this function in the LRS and implement it if appropriate. Suppliers of fluorescence free diamond chips have been identified, and lab tests are already proceeding at WU.