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Getting Light into a Monochromator
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In this section we give a brief introduction to getting light into a monochromator, and how much you can expect to get out. While the emphasis is on coupling Oriel Light Sources to Oriel Monochromators, the same general principles apply to collecting light from any source for analysis. Specifically, all of the collection principles we will cover here may be applied to spectrographs as well as monochromators. Throughout these pages, we use the term monochromator for both instruments.
Geometrical extent is discussed on see Light Collection and Systems Throughput. Here it is defined as G = AΩ, where A is the image area at an image plane in the system and Ω is the associated solid angle. We also note that the lowest geometrical extent of any component in an optical system limits system throughput. In many spectroscopic systems, the monochromator is the component with lowest geometrical extent. The geometrical extent of the monochromator is the product of the slit area and the solid angle of acceptance. Our 77200 and 77700 1/4 m Monochromators have larger geometrical extent than our smaller 1/8 m monochromators and spectrographs.
Once you have chosen your monochromator you can do nothing to increase it’s geometrical extent, so you must think about source and detector coupling. Here we offer some help to make sure that the input optics, which you can optimize, do not limit the system throughput.
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| Tech Note |
| If you are using a monochromator in conjunction with your source to provide a monochromatic excitation beam, stray light is usually a small concern; it is often the goal to get as much light into the system as possible, regardless of geometry. However, if you have a detector at the output, particularly a large area detector such as Oriel’s InstaSpec™ CCD, stray light may be an important consideration. You may improve the signal to noise ratio of your system by limiting the geometrical extent at the input to the monochromator. Our 77400 and 77700 models have | | | | |