Double monochromator MZDD350i

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The main limitation in research of weak spectral signals is a level of stray light. Stray light is mostly caused by quality of optical elements: mirrors and gratings. Besides, the stray light appears in the result of reflection of a spectrum from an entrance slit, a detector and from other structural units. The stray light can be minimized by using light absorbing partitions, by inclined installation of detectors, and by using holographic gratings.

Long-focus devices are characterized by lower stray light. Monochromators have lower stray light in comparison with spectrographs because the last named are used without any exit slit. Double monochromator is the best choice when the value of stray light is very important for research. With a double monochromator maximum suppression of stray light can be achieved.

MZDD350i is a double monochromator with zero dispersion consisting of two imaging monochromators MS3504i configured in one construction and the exit slit of the first monochromator is the entrance slit of the second monochromator. The device is fully automated. A set of four gratings and smoothly adjustable slits allow to operate in a wide spectral range with a required bandpass. 

Zero dispersion is reached by exact correspondence of beam pass through the first monochromator to a beam return through the second monochromator. Optical parameters of double monochromator with zero dispersion are determined by size of the entrance and intermediate (middle) slits and by aberrations of the first monochromator. The size of exit slit should be selected to avoid vignetting of the entrance slit image. The exit slit would be equal to entrance slit, if no aberration.

Table 1 shows the design parameters of exit slit depending on size of entrance and intermediate slits for MZDD350i (diffraction grating  1200 G/mm, wavelength 546 nm).

Table. 1.

Entrance slit, mm
Intermediate slit, mm
Exit slit, mm
0,025 2 0,031
0,5 2 0,52
1 2 1,05
1 1 1,04


Light at output in a single monochromator is a part of spectrum. The light leaving the double monochromator with zero dispersion is spectrally uniform at the output. This main feature, alongside with capability of maximum suppression of stray light, determines the fields of application of MZDD350i.



pdf icon2Brochure MZDD350i.pdf (download)





SOL instruments: спектрометр, рамановский микроскоп, эмиссионный спектрометр. book-2

Theory & Instructions
1. Spectral Instrument. Basic Concepts and Characteristics.
2. Spectral Devices. A Spectral Device Selection.
3. Spectra Detection. Detector Selection.



  • Spectral measuring instruments for UV, Visible and IR regions where tunable monochromatic light is wanted
    The MZDD350i can operate as a tunable filter with adjustable bandpass and extremely low straight light
  • Raman speсtroscopy
    Extremely low stray light allows to performs measurements close to the excitation laser line without using any Notch or Edge filter
  • Spectrosсopy of pulsed light sources
    There is almost zero broadening of light pulses after passing through the double monochromator thanks to exact inverse beam path in the second monochromator in regard to the first one. There is identical pass length for all wavelengths
  • Measurements of the CCD detectors quantum efficiency
    Light from the exit slit falls on the imaging detector and the light is measured with a calibrated detector simultaneously



  • Wide spectral range: UV, VIS, IR
  • Low stray light
  • High aperture
  • High wavelength accuracy and repeatability
  • Fully computer controlled


Optical layout and components

Optical layout of Double monochromator with dispersion subtraction based on MS3504i is shown in Fig.1. Optical components 1-6 and 14 belong to the 1st monochromator, optical elements 8 -12 belong to the 2nd monochromator. Spectral slit 7 is exit slit of the 1st monochromator and in the same time it is an entrance slit of the 2nd monochromator. Thit slit is called intermediate.

The 1st monochromator can be supplied optionally with motorized flip mirror 6. It allows to use axial output port of the 1st monochromator. The 1st monochromator will operate as imaging spectrograph in this case.

 Fig.1. MZDD350i Optical Layout

 Fig.1. MZDD350i Optical Layout

1 – entrance slit, 2 – flip mirror, 3 – collimating mirror, 4 – grating of 1st monochromator, 5 – camera mirror, 6 – motorized flip mirror, 7 – intermediate slit, 8 – motorized flip mirror, 9 – collimating mirror, 10 – grating of 2nd monochromator, 11 – camera mirror, 12 – flip mirror, 13 – exit slit, 14 – shutter