MZDD350i Double Monochromator

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.

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Description

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 spectrographsbecause 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.

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.

 

Applications

  • 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

 

Features

  • 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 1stmonochromator 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 1stmonochromator. 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

 

 

Optical System:

Configuration: Two imaging monochromators with Cherny-Turner optical scheme.
Monochromators are cascade situated for dispersion subtraction
Ports*: 1 input and 1 output
Wavelength range: 185 nm – 60 μm (depends on the type of grating)
F/number (entrance): 1/3.8
Mirror focal lengths: 300 mm and 350 mm
Scanning range, limited by grating rotation angle: 0 – 1270 nm (for 1200 l/mm grating)
Main mirrors: Spherical
Stray light: 5х10-10 (nm from laser line 632.8 nm)

*Axial exit port of the1st monochromator MS3504i can be used additionally.

Drive

Motor: Stepper, with fractional steps
Drive: Warm
Step size: 1.62 arc seconds
Precision: ± 1 step
Max.speed: 10 000 steps/s

*Optics

Spectral resolution: 0.07 nm
Repeatability: ± 0.03 nm
Wavelength accuracy: ± 0.06 nm
Average scanning step: 0.01 nm

*For grating 1200 l/mm, slit width 15 μm, wavelength – 546 nm

Gratings

Size: 70 х 70 х 10 mm
Rotation: About the center of grating working surface
Mounting: Automated 4-grating turret in each monochromator
Grating repeatability of monochromators
– *wavelength: ± 0.03 nm
– vertical image: ± 0.050 nm

* For grating 1200 l/mm, slit width 15 μm, wavelength – 546 nm

Spectral slits

Type of spectral slit: Automated (combined) Manual
Control: Automated (drive) or
manual (micrometer)
Manual by micrometer
Width: Regulated from 0 to 2.0 mm
Parallelism:  ± 1 μm
Accuracy (slit 1 mm):  ± 10 μm
Repeatability:  ± 1 μm  ± 1.5 μm
Reading accuracy (micrometer): 2 μm
Step size: 0.5 μm
Height: Diaphragm-regulated from 0 to 10 mm

Integrated shutter

Shut time: ~100 ms
Max. Frequency: 1 Hz
Control: On-board CPU or TTL-signals from the external device

Control

Central: On-board CPU
External: PC
External interface: Ethernet, USB

Power requirement

Supply voltage: (100…220) V, 50/60 Hz
Power consumption: Not more than 70 W

 

While choosing a device configuration a proper selection of diffraction gratings is important. A proper selection of diffraction grating allows one to obtain the best combination of high energetic efficiency and spectral resolution.

The basic grating parameters which determine their right choice you can find in the methodical material “Spectral Instrument. Basic Concepts and Characteristics.”

We propose a wide range of diffraction gratings to be used in MZDD350i.
Please, choose a necessary grating from the given below list, or consult our specialists.

SOL instruments: спектрометр, рамановский микроскоп, эмиссионный спектрометр. дифракционная решетка435х315

Basic parameters for correct selection of diffraction gratings:

In the Table “Selection of diffraction gratings” groove density and blaze wavelength belong to a diffraction grating parameters. Other parameters characterize a spectral device together with a selected grating.

  • Groove density. The diffraction grating has a periodic structure. Such parameters as resolving power and free spectral range are determined by the periodic structure properties of a diffraction grating. The period of grating is the distance through which grooves are repeated. The reciprocal value of a grating period is called the groove density and displays the number of grooves in 1 mm.
  • Blaze wavelength. The reflectivity of a grating depends on the grooves geometry, because the direction to the center of the diffraction maximum is determined by the mirror reflection of the incident beam from the edge of a groove. In spite of rather flat profile of diffraction maximum a blaze wavelength that corresponds to the maximum efficiency of the grating has been adopted as a feature for convenience of calculation.
    When selecting a grating it is useful to determine a blaze wavelength for a required grating on the spectral range of limited wavelengths  WL1 and WL2. The blaze wavelength is determined by the ratio:
    WLBlaze  = 2 ∙ WL1 ∙WL2 / (WL1 + WL2).
  • Reciprocal linear dispersion. The light from a grating in the focal plane of a spectral instrument forms a spectrum. Linear dispersion is used for a spectrum characteristic, which is defined as a reciprocal value of the product of angular dispersion of a grating and focal length of a spectral instrument and shows the spectral range that falls on a single linear distance in a focal plane.
  • The spectral resolution.  Limiting resolution of a spectral instrument is equal to the minimum half-width of its instrument function. The instrument function is determined by finite sizes of entrance diaphragm, aberrations and also distortions caused by inaccuracy in manufacturing and adjustment of optical elements of instrument. In addition, instrument function, and thus spectral resolution are dependent on lighting method of entrance slit, used aperture and registration system parameters.
  • Operating wavelength range. Energy efficiency range referred to the wavelength region in which grating reflection coefficient is not less than  0.405 of the maximum. In the first order this range is limited by the wavelengths: ⅔ ∙ WLBlazeand 2 ∙ WLBlaze.
    Operating range usually corresponds to a grating energy efficiency. In some cases, for gratings with a high groove density and large blaze wavelength, the long-wave border of operating spectral range of instrument is limited by a maximal rotation angle of a grating which is defined by design of instrument.

 

Table for selection of diffraction gratings

Model Line density,
mm-1
Blaze wavelength,
nm
 *Reciprocal linear dispersion,
nm/mm
Spectral resolution,
nm
Operating wavelengths range, nm  
Spectral range
limited by the grating rotation angle, nm
773600 3600 hol 0.76** 0.025 185 – 425 425
772422 2400 225 1.17 0.035 185 – 450 640
772427 2400 270 1.16 0.035 185 – 540 640
772770 2400 400 1.11 0.035 270 – 640 640
771827 1800 270 1.57 0.04 185 – 540 860
771840 1800 400 1.54 0.04 265 – 800 860
771850 1800 500 1.49 0.04 330 – 860 860
771875 1800 750 1.29 0.04 500 – 860 860
771225 1200 250 2.36 0.07 185 – 500 1280
771228 1200 280 2.36 0.07 185 – 560 1280
771240 1200 400 2.35 0.07 265 – 800 1280
771250 1200 500 2.33 0.07 330 – 1000 1280
771260 1200 600 2.30 0.07 400 – 1200 1280
771275 1200 750 2.24 0.07 500 – 1280 1280
770623 600 230 4.72 0.14 185 – 460 2560
770630 600 300 4.72 0.14 200 – 600 2560
770640 600 400 4.73 0.14 265 – 800 2560
770650 600 500 4.73 0.14 330 – 1000 2560
770660 600 600 4.73 0.14 400 – 1200 2560
770675 600 750 4.71 0.14 500 – 1500 2560
7704008 400 800 7.09 0.21 540 – 1600 3840
7704012 400 1200 7.06 0.21 800 – 2400 3840
7704017 400 1700 6.94 0.21 1135 – 3400 3840
7704020 400 2000 6.83 0.21 1335 – 3840 3840
7704025 400 2500 6.57 0.21 1665 – 3840 3840
770330 300 300 9.42 0.28 200 – 600 5120
770335 300 350 9.42 0.28 235 – 700 5120
770350 300 500 9.44 0.28 335 – 1000 5120
770360 300 600 9.45 0.28 400 – 1200 5120
770370 300 700 9.45 0.28 465 – 1400 5120
7703010 300 1000 9.46 0.28 665 – 2000 5120
7703015 300 1500 9.42 0.28 1000 – 3000 5120
7703020 300 2000 9.33 0.28 1335 – 4000 5120
7703030 300 3000 8.95 0.28 2000 – 5120 5120
7703035 300 3500 8.65 0.28 2335 – 5120 5120
770235 200 350 14.11 0.42 235 – 700 7680
770240 200 400 14.12 0.42 265 – 800 7680
770250 200 500 14.13 0.42 335 – 1000 7680
770270 200 700 14.15 0.42 465 – 1400 7680
7702015 200 1500 14.19 0.42 1000 – 3000 7680
7702020 200 2000 14.16 0.42 1335 – 4000 7680
7702025 200 2500 14.10 0.42 1665 – 5000 7680
7702030 200 3000 14.00 0.42 2000 – 6000 7680
771547 150 475 18.81 0.56 315 – 950 10300
771570 150 700 18.85 0.56 465 – 1400 10300
7715030 150 3000 18.85 0.56 2000 – 6000 10300
7715045 150 4500 18.52 0.56 3000 – 9000 10300
770165 100 650 28.21 0.84 435 – 1300 15400
770170 100 700 28.22 0.84 465 – 1400 15400
7701010 100 1000 28.26 0.84 665 – 2000 15400
7701020 100 2000 28.36 0.84 1335 – 4000 15400
7701025 100 2500 28.38 0.84 1665 – 5000 15400
7701030 100 3000 28.38 0.84 2000 – 6000 15400
7701042 100 4160 28.31 0.84 2800 – 8300 15400
7701048 100 4840 28.23 0.84 3300 – 9600 15400
7701055 100 5500 28.11 0.84 3700-11000 15400
7701062 100 6200 27.94 0.84 4200-12400 15400
7701072 100 7200 27.63 0.84 4900-14400 15400
7701088 100 8750 26.98 0.84 5900-15400 15400
7701097 100 9700 26.46 0.84 6500-15400 15400
7701103 100 10300 26.09 0.84 6900-15400 15400
7775070 75 7000 37.54 1.12 4700-14000 20600
7775095 75 9500 36.88 1.12 6400-19000 20600
7750010 50 1000 56.37 1.68 700-2000 31000
7750038 50 3800 56.70 1.68 2700-7600 31000
7750063 50 6300 56.75 1.68 4200-12600 31000
7750070 50 7000 56.73 1.68 4700-14000 31000
7750083 50 8300 56.63 1.68 5600-16600 31000
7750124 50 12360 55.89 1.68 8300-24700 31000
7750169 50 16900 54.25 1.68 11300-31000 31000
7750200 50 20000 52.56 1.68 13400-31000 31000
7737028 37.5 2790 75.38 2.24 1900-5500 41200
7737056 37.5 5570 75.63 2.24 3700-11100 41200
7737093 37.5 9260 75.64 2.24 6200-18500 41200
7737156 37.5 15600 74.74 2.24 10400-31200 41200
7724116 24 11600 118.25 3.5 7800-23200 64000
7724144 24 14400 118.19 3.5 9600-28800 64000
7724173 24 17300 117.97 3.5 11600-34600 64000
7724243 24 24300 116.81 3.5 16200-48600 64000
7724285 24 28500 115.65 3.5 19000-57000 64000
7724325 24 32500 114.20 3.5 21700-63000 64000

 

* For the 1st monochromator at the blaze wavelength

** at the wavelength 225 nm