PHOTON RT UV-VIS-MWIR Spectrophotometer

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.

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.

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

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.

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.

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

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

Ordering:
P/N 048.010.000 

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

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

Ordering:
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

Application:
Sequential baseline calibration and measurement of multiple samples with equal diameter

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

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

Metric
- 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

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

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

Features:
- 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

Ordering:
P/N 048.028.100

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

Features:
- 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

Ordering:
P/N 048.028.200

Application:
Unattended transmission measurement of multizone filters and linear variable filters.

Features:
- 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. 

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

Application:

3D reflection/transmission analyses

Features:
- 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

Ordering:
P/N 048.034.000

Application:
Determination of the optimal rotation angle of the wave plate axis

Features:
- 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

Ordering: 
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

Application:
Transmission measurement of the wave plates

Features:
- 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

Ordering: 
P/N 048.035.000

Application:

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

Features:
- Transmission / Reflection
- Variable AOI up to 75 deg

Ordering:
P/N 048.032.000

Application:
Transmission and reflection measurements at 70 - 85 deg AOI

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

Ordering:
P/N 048.033.000