Subtractive double monochromator

Figure 3.5-1 Types of Raman spectrometers a scanning spectrometer with triple additive monochromators, S source, D detector b instrument with subtractive double monochromator combined with polychromator and array detector AD c Rayleigh filter RF with polychromator and array detector.

Michelson interferometers can be combined with Rayleigh line filters (or subtractive double monochromators) in order to prevent the consequences of the multiplex disadvantage (Secs. 3.1.6, 3.3.6 Fig. 3.4-1). 

Figure 8.12. Schematic of a triple spectrograph, consisting of a subtractive dispersion double monochromator preceding a single spectrograph. Similar to Spex Triplemate" or Dilor X-Y. ...

In the TRPL measurements performed at 2K the excitation was made by a Ti sapphire laser system, with spectrally narrow (< 1 meV) 2 ps pulses. The emitted light was dispersed by a subtractive double-grating monochromator and detected with a multi-channel plate photomultiplier in the photon-counting mode with a time resolution of 20 ps. 

Pulse dispersion and pulse shift can be avoided by using a double monochromator of the subtractive dispersion type. In this design the second monochromator is turned 180 °, and the gratings are moving in opposite directions. Thus the path length differences for both sides of the gratings and for different wavelength cancel. 

Fig. 4.6 Block diagram of a conventional multichannel Raman spectrometer. S, sample. Note, the double monochromator is operating in subtractive mode.

Subtractive double-grating monochromator with moving intermediate slit... 

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