This tunable double monochromator is applicable to any laser wavelength. The gratings of the McPherson Model 275DS operate in a subtractive dispersion mode. Actual bandwidth passing through this filter monochromator can be adjusted via the individual slit widths. The cut-off wavelength can be adjusted so that the laser wavelength is suppressed. The width of the selected bandpass covers the whole Raman spectrum excluding the laser line. The filtered Raman emission is tightly refocused onto the entrance slit of the primary monochromator for ultimate Raman dispersion and CCD detection.
The above is an example of a Raman system consisting of a McPherson Model 275DS 0.2 m focal length subtractive double monochromator mounted on a McPherson Model 207 0.67 m focal length primary Raman disperser with a cooled CCD.
The figure above shows an example of a high resolution Raman spectrum of CCL, taken with a 2400 G/mm grating. The isotope structure is clearly visible.
This filtering double monochromator has excellent stray light rejection. The McPherson Model 275DS provides a variable and sharp band, and also obtains OD 6 only 3 nm (100 cm-1 @ 514 nm excitation) away from the halfwidth of the bandpass, as shown in the figure below. This allows users to achieve information closer to the laser excitation line and outperforming the best notch filters claiming OD 6 at 4 nm away from the halfwidth wavelength.
