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DTMc300 Double Monochromator

  • DTMc300 double monochromator connectors
  • DTMc300 double monochromator entrance and exit slits
  • Compact configuration DTMc300 double monochromator

In each component monochromator, up to 3 diffraction gratings feature to permit measurements over a wide spectral range. Multiple configurations are achieved via the addition, at the entrance/ exit ports of each, of an additional slit with a computer-controlled selection mirror (SAM).

Delivering best uncertainty in detector responsivity and time resolved measurements, the DTMc300 may be arranged in the additive dispersion mode, applicable in solutions incorporating a UV component, and subtractive dispersion mode, sought by high level laboratories requiring unsurpassed accuracy and complete measurement confidence.

Core benefits


  • High configurational flexibility
  • Double monochromator comprising two TMc300 focal length monochromators
  • Czerny-Turner configuration, arranged for either additive or subtractive dispersion
  • Each single monochromator accommodates up to three diffraction gratings permitting single–scan measurement over wide spectral range (200nm-50µm)
  • Up to two entrance ports, one exit port on first monochromator (single mode) and one entrance port on the second monochromator (single mode)
  • Automated mirror-based port selection for use of multiple input/ output/ detector configurations

Optical Layout

ConfigurationPair symmetrical Czerny Turner monochromators arranged for either additive or subtractive dispersion
Focal lengthTotal focal length: 600mm (additive)
Individual Units: 300mm
Grating mountTriple grating turret
Number of gratings1-3
Grating size68 x 84mm
Aperture ratiof/4.1 (at all grating angles)
Number of entrance/ exit ports1 or 2 in both monochromators


Mechanical resolution drive0.000072°/ step
Slit typeFixed, micrometer or motorised variable
Slit width & height10µm-10mm (W) x 20mm (H)
Filter size23/25mm diameter

Optical Performance (quoted for 1200 g/mm gratings)

Spectral rangeWithin range 200nm-50µm
Linear dispersion1.35nm/mm (additive)
Wavelength accuracy± 0.1nm
Wavelength reproducibility± 0.025nm
Resolution full/reduced slit height0.15/0.05nm
Stray light rejection at 2.5 FWHM10-8
Wavelength acquisition speed2000nm/s


Computer interfaceUSB 2.0
Software controlBenWin+/SDK

Electrical/ Mechanical

Overall dimensions 634L x 360W x 211H
Optical height 115mm
Weight28 kg
Power supplyMains input 110/220V 50/60Hz


Diffraction gratingsSee Configurations Tab
Order sorting filtersSee Configurations Tab
Filter wheel252-6 or 252-8 (6/8-position filter wheel, includes shutter)

Diffraction Gratings

A range of gratings are available depending on the spectral range of consideration, with up to three diffraction gratings mounted to each turret of the DTMc300.

GratingLine density (g/mm)Grating type & Blaze wavelengthMaximum wavelength range (nm)
GA-T324R0U252400Plane ruled, 250nm blaze200-600
GA-T324H0U252400Plane holographic, 250nm blaze200-600
GA-T324H0U32400Plane ruled, 300nm blaze200-600
GA-T318H0U251800Plane holographic, 250nm blaze250-900
GA-T318R0U41800Plane ruled, 400nm blaze250-900
GA-T318R0U51800Plane ruled, 500nm blaze250-900
GA-T312H0U251200Plane holographic, 250nm blaze300-1,200
GA-T312R0U41200Plane ruled, 400nm blaze300-1,200
GA-T312R0U51200Plane ruled, 500nm blaze300-1,200
GA-T312R0U751200Plane ruled, 750nm blaze300-1,200
GA-T312R0U91200Plane ruled, 900nm blaze300-1,200
GA-T312R1U01200Plane ruled, 1µm blaze300-1,200
GA-T3083R1U2830Plane ruled, 1.2µm blaze600-1,800
GA-T306R1U0600Plane ruled, 1µm blaze800-2,500
GA-T306R1U25600Plane ruled, 1.25µm blaze800-2,500
GA-T306R1U6600Plane ruled, 1.6µm blaze800-2,500
GA-T306R1U9600Plane ruled, 1.9µm blaze800-2,500
GA-T306R2U16600Plane ruled, 2.16µm blaze800-2,500
GA-T304R1U6400Plane ruled, 1.6µm blaze1,000-3,000
GA-T303R3U0300Plane ruled, 3µm blaze1,500-5,500
GA-T303R4U0300Plane ruled, 4µm blaze1,500-5,500
GA-T3015R4U0-AU150Plane ruled, 4µm blaze. Gold coated.3,000-10,000
GA-T3015R6U0-AU150Plane ruled, 6µm blaze. Gold coated.3,000-10,000
GA-T301R9U0-AU100Plane ruled, 9µm blaze. Gold coated.4,500-16,000
GA-T30075R10U0-AU75Plane ruled, 10µm blaze. Gold coated.6,000-20,000
GA-T30075R12U0-AU75Plane ruled, 12µm blaze. Gold coated.6,000-20,000
GA-T3005R18U0-AU50Plane ruled, 18µm blaze. Gold coated.9,000-30,000
GA-T3005R19U5-AU50Plane ruled, 19.5µm blaze. Gold coated.9,000-30,000


Slit typeFeatures
Fixed slits (FSS)- Manually controlled
- Spring leaf to ensure the correct placement of the slit
Micrometer variable slits (VSS)- Manually controlled
- Bi-lateral slits
- Variable from 10µm to 10mm
Motorised variable slits (MVSS)- PC control via USB
- Driven via internal monochromator electronics or external MAC electronics bin
- Comprising stepping motor driven bi-lateral slits
- Variable from 10µm to 10mm


An order sorting filter wheel is located inside the entrance port of the monochromator, fitted with 6 or 8 filters selected for the spectral range of use.

When measuring below 400nm, no filters are required as the corresponding wavelength of the subsequent diffraction order is less than 200nm, which is naturally blocked by the atmosphere.

Spectral rangeRequired OS filter
<400 nmNone
400-700 nmOS400
700-1250 nmOS700
1250-2000 nmOS1250
2000-3600 nmOS2000
3.6-6 µmOS3600
6-10.5 µmOS6000
10.5-21 µmOS10500
> 21 µmPlease consult.

Further Options

ND/ BP filtersNeutral density filters, used to attenuate optical signal level or band pass filters, to improve monochromator stray light performance, may be mounted in the filter wheel.
Purge portsPurge ports fitted to monochromator to allow purging with nitrogen to remove atmospheric absorbants which absorb in the UV (<200nm) and IR (Various absorption bands).
Toroidal mirrorsToroidal mirrors spherical mirrors replaced with toroidal mirrors for imaging applications.
Turret-mirrorA mirror may be fitted on a free location on the turret for the purposes of relating un-diffracted light to the exit port.
418-INT418 optical chopper mounted behind the entrance slit.
Interchangeable turretsFor applications where very wide spectral range or regional optimisation is required, an interchangeable turret is available allowing the exchange of groups of three diffraction gratings to cover different spectral regions. In this case, the stepping motor in this case drives a platform to which is attached the grating assembly.
ShutterSolenoid-based shutter for timed exposure applications.

Monochromator Dimensions

DTMc300 double monochromator front dimensions
DTMc300 monochromator profile - Front profile
DTMc300 double monochromator side dimensions
DTMc300 monochromator profile - Side profile
DTMc300 double monochromator top dimensions
DTMc300 monochromator profile - Top profile

Software Control

The DTMc300 may be controlled by PC, facilitated via a USB 2.0 interface by Bentham’s Benwin+ spectroradiometer software, responsible for:

  • Accessing grating filter wheel and slit properties
  • Identifying grating type and position
  • Wavelength selection and calibration
  • Spectral measurements
  • System calibration
  • Configuration files syntax

Alternatively, Bentham offers a comprehensive SDK for user-written programs, available across a wide range of platforms (LabVIEW, Matlab, C++, SCPI protocol, etc.).

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