PHOTON RT UV-VIS-MWIR Spectrophotometers for Coaters


  • World's first spectrophotometer designed for optical coaters
  • World's only instrument to feature UV-MWIR (220-5200 nm) polarization measurement capability, a unique opportunity offering deeper insight into real performance of optical coatings

The PHOTON RT UV-VIS-MWIR scanning spectrophotometer is designed specifically for unattended measurement of optical samples with coatings. The instrument is produced in six configurations relative to the effective wavelength range - from 185 nm up to 5200 nm.


  • Record-wide wavelength range configuration in a single instrument: 185-5200 nm
  • More than 10 times faster measurement compared to other tools on the market
  • No need to re-calibrate the baseline after change of angle of incidence
  • Measurement of transmittance and absolute specular reflectance from the same area on the substrate – perfect for backward analyses of thin film design
  • The state-of-art measurement channel head represents the most complex and capable mechanism of its kind to be used for characterizing of coatings at different AOIs, polarizations, with wide range of beam deviation and beam displacement up to +/- 60,0 mm
  • Fully unattended measurement of sophisticated single-element and cemented prisms: beamsplitters, dove prisms, right angle prisms, penta and half penta prisms, rhomboid prisms, roof prisms, Schmidt prisms, Pechan prisms. Prisms can be mounted or unmounted.
  • Radically minimized human errors in the measurement process due to fully automated procedures
  • Silent and smooth mechanism for lifting and lowering the lid


PHOTON RT Multifunctional Spectrophotometer. Technical Specifications

  PHOTON RT Spectrophotometer. Product Configuration
MODEL 0217 0235 0252 0417 0435 0452
Photometric functions %T, %R
Effective wavelength range, nm 185 - 1700 185 - 3500 185 - 5200 380 - 1700 380 - 3500 380 - 5200
Built-in polarizer, nm 220 - 1700 220 - 3500 220 - 5200 380 - 1700 380 - 3500 380 - 5200
Optical scheme of monochromator Czerny-Turner
Optics Mirror, MgF2
Reference channel Yes
Wavelength sampling pitch, nm  0,1 - 100
Spot size on the measured sample, mm 6 x 2 > 2 x 2
Turning pitch angle of sample stage 0,01 deg
Turning pitch angle of photodetectors 0,01 deg
Beam displacement compensation -60,0 mm ... 0 ... +60,0 mm (actual value depends on detector position)
Variable angle measurements

1. 0 - 75 deg for transmittance (up to 85 deg with 7085 sample stage)

2. 8 - 75 deg for absolute reflectance (up to 85 deg with 7085 sample stage)

3. Detector rotation range: 300 deg ... 180 deg ... 16 deg

4. Sample stage rotation range: -85 deg ... 0 deg ... +85 deg

Wavelength subranges, nm Ultimate spectral resolution, nm (non-polarized light) Wavelength accuracy, nm Wavelength repeat accuracy, nm
185 - 350 nm 0,3 +/- 0,25 +/- 0,125
350 (380) - 990 nm 0,6 +/- 0,5 +/- 0,25
990 - 1650 nm 1,2 +/- 1,0 +/- 0,5
1650 - 2450 nm 1,2 +/- 1,0 +/- 0,5
2450 - 5200 nm 2,4 +/- 2,0 +/- 2,0
Stray light level, % at 532 nm ˂0,1
Angle of beam divergence +/-1 deg
Photometric accuracy


NIST SRM 930e: +/-0,003 Abs (1Abs)

NIST SRM 1930: +/-0,003 Abs (0.33Abs); +/-0,006 Abs (2Abs)


NRC NG11 SRM: +/-0,0013 Abs (0,13 Abs); +/-0,0053 Abs (0,49 Abs); +/-0,0011 Abs (0,82 Abs); +/-0,005 Abs (1,0 Abs)

Determined using 0,1 second accumulation, maximum deviation for 10 subsequent measurements

Photometric repeat accuracy (VIS range)


NIST SRM 930e: 0,0004 Abs (1 Abs)

NIST SRM 1930: 0,0001 Abs (0,33 Abs); 0,005 Abs (2 Abs)


NRC NG11 SRM: +/-0,0003 Abs (0,13 Abs); +/-0,0008 Abs (0,49 Abs); +/-0,0022 Abs (0,82 Abs); +/-0,0034 Abs (1,0 Abs)

Determined using 0,1 second accumulation, maximum deviation for 10 subsequent measurements

Stability of baseline, %/hour (VIS range) ˂0,1 (one hour warm-up time)
Unattended polarization measurements with built-in polarizers
  1. S, P, (S + P) / 2, Random
  2. User defined S:P ratio for incident beam (20 / 80, 30 / 70 etc)
Zero order / Green beam Built-in, automatic
Light sources, preinstalled

1. Halogen lamp: 1 ea

2. HgAr wavelength calibration verification lamp: 1 ea

  Deuterium lamp: 1 ea Deuterium lamp: 1 ea Deuterium lamp: 1 ea      
      IR source: 1 ea     IR source: 1 ea
Light sources, spare Halogen lamp: 2 ea (included with shipment). Other spare light sources can be ordered
Dovetail baseplate for sample stages Designed for mounting of motorized and non-motorized sample stages. Integrated controller ensures instant detection of the motorized stage
Planar sample stage

For measurement of transmission and reflection of planar samples with size bigger than 12,0 x 10,0 mm

Independent positioning

Independent computer controlled positioning of sample stage and photodetectors unit

Synchronized positioning Synchronized computer controlled positioning of sample stage and photodetectors unit dependingon the selected photometric function 
Size of samples

Min. 12,0 x 10,0 mm - for measurement at 0 - 10 deg incidence angles

Min. 12,0 x 25,0 mm - for measurement at 10 - 75 deg incidence angles

Max. sample size:

  • up to 152,4 mm (6") with closed lid for standard sample stage
  • up to 140,0 mm (5 1/2") with closed lid for Z sample stage
Sample stage for PBS cubes 50,0 x 50,0 x 50,0 mm sample stage with two additional cube holders 1" x 1" x 1" and 1/2" x 1/2" x 1/2"
Optional motorized and non-motorized sample stage
  1. MP Stage. Multiple sample measurement
  2. XY Stage. XY sample mapping
  3. XY-MZF Stage. Measurement of multi-zone filters and linear variable filters
  4. Z Stage. Sequential baseline calibration and sample measurement without opening the lid
  5. QW Stage. Testing of wave plates
  6. R Stage. 360 deg rotation of the sample around the beam axis
  7. 7085 Stage. Measurement at extreme angles of incidence up to 85 deg
Interface USB 2.0, Windows-based, English
File saving formats res (txt), xls, pdf, csv
Power consumption, Watt 110
Power input 110 - 220 V (+/-10%), 50 - 60 Hz
Width х Depth х Height, mm (inches) 425 x 625 x 285 (16 3/4" x 24 2/3" x 10 1/5")
Net weight, kg (lbs) 50 (110)
Measurements at extreme angles of incidence

Modern optical coatings often operate at high angles of incidence (AOI) thus offering unique features to photonics devices. A typical high angle is 45 degree, or Brewster angle. Polarizing coatings are also specified for operation at 72 deg AOI for growing number of applications. This measurement need is already met with our standard PHOTON RT configuration both for transmission and reflection.

A few of our customers have recently inquired if we can develop a solution to measure coatings at extreme angles of incidence, like 80 or 85 degrees. Under this challenging specification, the beam travels very close to the substrate’s surface, so the beam projection expands dramatically. Additionally, the full beam energy must enter the substrate and reach the detector both in transmission or reflection mode, without any losses. Finally, S and P polarization states shall be clearly defined, separated and measured.

Jointly with one of our customers, EssentOptics engineers developed a separate sample stage for measurement of transmission and reflection seamlessly from 70 up to 85 deg AOI.

Images below show our “7085” sample stage with a test sample installed and measurements results of transmission and reflection at 8, 70 and 85 deg AOI, including S and P polarizations. We used a broadband high reflection mirror to demonstrate measurement capabilities using the “7085” stage. These results demonstrate that even measurements at extreme angles of incidence can be successfully performed using the PHOTON RT spectrophotometer.


Changing of the spot size

Although there is no “standard” samples size, typically our customers use 1 inch samples for witness pieces or samples with 10,0 mm diameter and bigger for commercial applications.

However, there are plenty of applications with smaller size samples, like 5,0, 4,0 and even 3,0 mm diameter. Engineers usually face a problem of measuring such samples. Traditionally they use witness pieces to assess transmission or reflection. These pieces are placed either in the test slide changer or in the close proximity to the commercial samples located on the calotte. Depending on the uniformity level achieved in the vacuum chamber, the coating on the commercial sample can have certain degree of mismatch with that on the witness piece.

We have received a number of requests to find a solution to measure small samples. As a result of our R&D we have provided our customers with a few different attachments that reduce the spot size on the sample. However, the use of them is associated with extra engineer’s time for careful alignment of the fixture and the sample. The solutions are not also perfect when the engineer has different samples in the batch and needs to measure them sequentially.

Engineers at EssentOptics were puzzled with this problem for a number of years. Several brainstorming sessions have eventually led to a breakthrough design changes in the PHOTON RT spectrophotometer. The new design of motorized slits now enables our customers to change the spot height smoothly from almost 6,0 x 2,0 mm to 2,0 x 2,0 mm with just a click of a button. The engineer can set the desired slit size to meet the actual clear aperture of the sample. Video below demonstrates the process of changing the spot size on the sample with PHOTON RT spectrophotometer.


Measurement of UV optical coatings: getting the meaningful results

Measurements of UV optical coatings are often needed across the photonics industry. Wide range of UV coatings has been developed for various applications:

  • UV-Enhanced aluminum mirrors and multilayer UV mirrors are used in lasers and other types of optical systems for beam steering or reflecting needs. They operate at different AOI ranging from 0 deg to 45 deg, observing also polarization requirements. Typical applications of UV mirrors include UV-curing-machines, UV-exposure machines, disinfection systems, medical instruments, sensor filters and other setups where ultraviolet heat / light separation is required.
  • UV antireflective coatings increase transmission and enhance contrast. They also reduces scattered light in imaging devices and second-surface reflections of beamsplitters
  • UV beamsplitters, UV notch filters and UV narrowband/wideband filters are designed for low power applications and can be found in many research and industrial installations.

The following specific performance features of metrology-grade spectrophotometers are the essential prerequisites to enable meaningful UV measurements:

  • low noise / high stability baseline
  • low internal noise of the instrument
  • low stray light.

The combination of these factors effectively increases the quality level of the measurement results. PHOTON RT spectrophotometer is designed to meet the above critical criteria as standard.

PHOTON RT: Low noise / high stability baseline (UV range)
Test procedure: 14 consecutive measurements during one hour

PHOTON RT: Low internal noise of the instrument (UV range)
Test procedure: Transmission measurement with fully blocked measurement channel

PHOTON RT: Low stray light (UV range)
Test procedure: Transmission measurement of borosilicate glass with no transmission in UV

Shown below are examples of UV mirrors and UV AR coatings measured with PHOTON RT spectrophotometer. Standard product settings with no smoothing were used for all tests.

Example 1: UV mirror optimized for 193 nm

Example 2: UV mirror optimized for 340 nm. S/P Reflectace @ 30, 45, 60 deg AOI

Example 3: UV AR coating optimized for 203 nm

Measurement of beamsplitter cubes at variable AOI's

Beamsplitter cubes are optical components used to separate a light into two beams (sometimes three beams, like X-cubes or RGB-cubes) at a designated T/R ratio. The cube consists of two cemented right-angle prisms typically with a multilayer interference coating on the internal hypotenuse, and all other four faces are AR coated to reduce losses due to reflection. Beamsplitter cubes can be premounted or unmounted.

Beamsplitter cubes can be non-polarizing (dichroic), polarizing or intensity splitters.

  • Non-polarizing or dichroic beamsplitters are designed to split incident light by its wavelength
  • Intensity beamsplitters are used when the incident light needs to be separated by a pre-defined ratio regardless to the polarization state light's wavelength
  • Polarizing cube beamsplitters are designed to split incident light into its polarized components rather than by simple transmission and reflection. The quality of the polarized cube is typically defined by the extent and accurate beam deviation of the transmitted and reflected polarized light and by the extinction ratio of the cube.

Traditionally the cubes were measured at normal angle of incidence. However, new photonic instruments utilize advance designs where beamsplitters can occasionally or specifically operate at variable AOI’s (augmented reality devices, optical computers, next generation projecting systems etc).

Virtually any beamsplitter cubes can be successfully measured with PHOTON RT spectrophotometer at normal or variable AOI’s. Below are a few amazing examples showing capabilities of PHOTON RT spectrophotometer.

Example 1
S-pol and P-pol transmission and absolute reflection measurement of a miniature polarizing cube (just 5,0 x 5,0 mm size) at normal AOI and also negative/positive AOI's. The max AOI we reached was 22 deg.


Example 2
S-pol and P-pol transmission measurement of 1” cube at +20 / -20 deg AOI with 1 deg step

Example 3
S-pol and P-pol transmission and absolute reflection measurement of the X-cube.

UV-MWIR Broadband measurements

One of the truly unique features of PHOTON RT spectrophotometer is the capability to run broadband measurements. The most sophisticated configuration offers an unsurpassed opportunity to qualify optical coatings for 185 - 5200 nm. 

Throughout our business history, we regularly set new benchmarks for broadband measurement capability. Since our first announcement of 380 - 2500 nm configuration of PHOTON RT many years ago, we have persistently looked for technical solutions, developed new technologies, and conducted tests to expand the spectral range of the instrument. Each new milestone we reached was a new challenge for our team. Each new frontier required more unique solutions.

Many of our customers consider PHOTON RT a product-of-choice for coaters, especially for its world-record broadband measurement capability.

Shown below is an example of single-run broadband absolute specular reflectance measurement of Au mirror. Layer thickness exceeds 50 nm. Standard product settings were used.

Standard stage. Non-Motorized

Transmission and reflection measurements at 0 - 75 deg AOI
* Included in the basic delivery set

- for measurement of planar samples
- Transmission / Reflection
- Variable AOI: up to 75 deg

P/N 048.010.000 

Standard stage for prism measurements. Non-Motorized

For measurement of transmission and reflection of prisms
* Included in the basic delivery set

- Transmission / Reflection
- Variable AOI
- Built-in beam offset correction depending on refractive index, sample thickness, angle of incidence

1. Stage base: P/N 048.027.000
2. Inserts:
- 1": P/N 033.016.108
- 1/2": P/N 033.016.110
- Inserts for prisms measurement of other shapes and sizes are also available on request

MP10 TR45 stage. Multiposition. Motorized

Sequential baseline calibration and measurement of multiple samples with equal diameter

- Transmission
- Variable AOI up to 45 deg
- Measurements of reflection are not specified


1. Stage base: P/N 048.038.000
2. Multiposition wheel:

- 30,0 mm x 10 pos: P/N 048.038.660
- 25,0 mm x 10 pos: P/N 048.038.640
- 12,5 mm x 20 pos: P/N 048.038.610

- 1" x 10 pos: P/N 048.038.650
- 1/2" x 20 pos: P/N 048.038.620

XY TR45 stage. Motorized

XY mapping of the sample for verification of the uniformity of the coating

- X range: +/- 25,0 mm
- Y range: +/- 20,0 mm
- Mapping area: 50,0 x 40,0 mm
- Sample size: 134,0 x 91,0 mm
- Transmission / Reflection
- Variable AOI up to 45 deg

P/N 048.028.100

XY T10 stage. Motorized

XY mapping of the sample for verification of the uniformity of the coating

- X range: +/- 55,0 mm
- Y range: +/- 20,0 mm
- Mapping area: 110,0 х 40,0 mm
- Sample size: 180,0 x 91,0 mm
- Transmission
- Variable AOI up to 10 deg

P/N 048.028.200

XY-MZF stage. Motorized

Unattended transmission measurement of multizone filters and linear variable filters.

- 0,3 mm width of the beam spot
- Width of individual filter zone down to 0,7 mm
- Measurement step down to 0,1 mm
- Maximum coated filter area (X Y): 50,0 x 40,0 mm
- Computer-controlled zone detection, zone centering / measurement, filter mapping. 

1. Stage base: P/N 048.041.000
2. Filter holders are custom designed


R stage. Motorized


3D reflection/transmission analyses

- Features 0-360 deg sample rotation along beam axis
- Max sample size: 70,0 mm diameter
- Min sample size: 25,0 mm diameter
- Transmission / Reflection.
- Variable AOI up to 60 deg

P/N 048.034.000

QW stage. Motorized

Determination of the optimal rotation angle of the wave plate axis

- Sample diameter: 0.5”, 1”
- Rotation angle of the sample along beam axis: +/- 45 deg
- Scan step for wave plate rotation angle: 0.1 - 5.0 deg
- Tilt angle of the sample to beam axis: 3 deg
- Selection of built-in analyzers UV-VIS-MWIR

1. QW-Stage, motorized (220 - 2200 nm analyzer): P/N 048.035.510
2. QW-Stage, motorized (380 - 2200 nm analyzer): P/N 048.035.520
3. QW-Stage, motorized (1500 - 5000 nm analyzer): P/N 048.035.530

QW stage. Non-Motorized

Transmission measurement of the wave plates

- QW plate is placed and fixed at 4 deg turned angle towards the beam
- QW plate is manually rotated with a hand lever: at +/- 45 deg
- QW plate size: 1” (25,4 mm) diameter
- High contrast analyzer is pre-installed and pre-aligned. CA 9,0 x 9,0 mm, OD 20,0 mm 
- WL range: 350 - 2200 nm

P/N 048.035.000

Z stage. Motorized


Unattended baseline calibration and measurement of the sample without opening the lid. Especially useful when the sample needs to be Nitrogen purged and measured under the same ambient conditions

- Transmission / Reflection
- Variable AOI up to 75 deg

P/N 048.032.000

7085 stage. Non-Motorized

Transmission and reflection measurements at 70 - 85 deg AOI

- Transmission / Reflection
- Variable AOI up to 70 - 85 deg


P/N 048.033.000