Ocean Optics MMS Raman - Manual (Page 20)

B: Introduction to Multimodal Sampling
An MMS-based spectrometer samples nearly 1,000 optical channels simultaneously through a coded
aperture – instead of a slit – then applies proprietary algorithms to precisely construct the spectral content
of a source. With MMS technology, both resolution and throughput (aka etendue) can be maintained and
optimized in a single-shot measurement. Interestingly, while the exact performance advantages of MMS
vary with the particular circumstances, in no case can a fiber or slit input spectrometer outperform an
identically configured MMS system.
The most dramatic MMS performance advantage is realized when making difficult measurements such as
measuring weak, scattering and/or diffuse sources commonly occurring in life science applications as well
as field or portable use. Diffuse and scattering samples are particularly challenging for conventional
sensors to measure because light collection is extremely low and thus, spectral features of interest are
flattened or are not detected at all. MMS systems inherently alleviate this problem. Furthermore, MMS
technology can be used for UV-Visible, NIR, Fluorescence and Raman spectroscopy. In this whitepaper,
we will provide an overview of MMS and compare its performance to slit/fiber based spectrometers.
Theory of Operation
The layout of a typical MMS spectrometer is shown in Figure 2. This particular design uses a dispersive
grating geometry with a coded aperture in place of a traditional slit/fiber. Light enters the system through
the coded aperture and is collimated onto the grating by a collimating lens. The grating spectrally
disperses the light which is then mapped
to a 2-D detector array such as a CCD.
The dispersive element could be a
transmissive volume phase hologram or a
reflective holographic grating depending
on the spectral range and other system
design parameters. It is important to note
that the MMS technology platform can b
implemented using a wide variety of
optical designs and be applied to any
spectral range.
e
Figure 2: Schematic of a MMS spectrometer
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