270M
Rapid
Scanning
Imaging
Spectrograph
Contact your Spex sales representative for detailed information and advice in selecting
gratings for your specific applications. In order to assure you
of
optimal selections for
your applications, we need
to
know:
•
•
•
•
•
•
•
The total range of wavelengths you wish to work over
The spectral resolution / bandpass you need
The type of source you are using
The spectroscopic phenomenon you will observe,
i.e.,
emission,
absorption, transmission, fluorescence, Raman, etc.
The type and spectral response of your detector
If an array detector is used, the size if the pixels and the array size
For arrays also, the coverage required
in
a single readout .
8.2 Optical Coupling at the Entrance Slits:
To allow the 270M
to
provide its maximum throughput, one
of
the most important
considerations is the proper coupling of light into the entrance slit. The Ideal is
to
maximize the signal
of
interest, while minimizing noise. To accomplish this, some
understanding
of
the optical requirements is helpful.
The 270M, like most spectrometers, is
an
imaging system. An image at the entrance
slit will be dispersed into its various wavelengths, and for each wavelength present in
the signal, an image
of
the entrance image
(as
masked by the entrance slit) will be
formed at the exit.
The best results are obtained when your signal is imaged on the entrance slit, on the
optical axis that is defined by the center of the slit and the center
of
the collimating
mirror. If the signal is visible
light,
a quick check can be made by placing a white card
in front of the collimating mirror. You should see homogeneous illumination across the
entire active surface. If some image or structure is observed in the card, the image is
probably not well focused at the entrance.
To optimize the signal
to
noise ratio, it is important that the collimating mirror is filled,
but not overfilled
by
the signal beam. Underfilling usually implies that more signal can
be obtained, by using faster collection optics. Overfilling the spectrometer optics can
only increase the possibility
of
stray light reaching the detector. Limit the aperture of
the beam so that the collimating mirror is just filled.
30
Revised November 24,
1992
Leica Microsystems, Inc.'s Ex. 1033
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