CT7: handheld reflectometer scatterometer
Description
The CT7 reflectometer / scatterometer is as of today the reference instrument to monitor the reflectivity and scattering of telescope's mirror coatings. This instrument is specially thought for accurate long term assessment of the mirror coatings and is in use on the most advanced telescopes worldwide.
The
CT7 is the greatly improved successor of the renowned
Iris instrument developed by
DMO. Its technology relies on the unmatched algorithm devised by
Dr Daniel Malaise. It provides a far better accuracy (0.2%) and repeatability (0.01%) than any other available measuring apparatus. And all of this in the palm of your hand: the instrument is 88mm long, 65mm wide and 130mm high, and weighs less than 600 gram! It’s designed to measure any surface safely and easily, in any environment.
The CT7 reflectometer / scatterometer works on batteries and can thus easily be taken with on the surface to be measured. The CT7 is positioned by a three-point soft contact. Curved mirrors can be measured without correction down to a radius of + or – 1m. You can save up to 10.000 measures and set the instrument to take a measure in loop at chosen intervals in console operation.
To read the measures, connect the reflectometer / scatterometer to your computing station, and open the included software CT7 Console. You get all the results in an easy to read table, you can configure your results sheets, copy-paste to excell or export them easily in a .cvs file to save or share.
The instrument comes with an in-depth documentation. We are also providing a constant customer service and are happy to answer all your questions and help you getting started or manage unexpected events.
Reflectivity monitor
The CT7 is primarly a reflectometer especially designed to measure the specular reflectivity of telescope's coating in 7 wavelength bands. It has an acceptance angle of 1.5° (half angle) and works at 8° incidence. The 7 Bands can be chosen in the UV-Visible-NIR region; current choice is the following:
Wavelength (nm) |
Bandpass (nm) |
365 |
10 |
420 |
25 |
528 |
30 |
630 |
20 |
730 |
50 |
850 |
50 |
940 |
40 |
The sources are modulated at a frequency around 2kHz and detected by the technique of digital lock in amplifier based on a DSP board. This makes the instrument immune to stray light.
Two identical detectors are used; one to measure the reference signal of the source, the other to measure the reflected signal. Both signals are digitally detected and the ratio of the source signal to the reference signal is recorded and processed to yield the reflectivity value. Each color is lit and measured sequentially for one second.
The two detectors are mounted on the same heat sink. This ensures a long-term absolute stability and immunity against temperature variations even when the sources degrade or vary in intensity. Since 2016, the detectors are selected for showing identical temperature sensitivity curves. This instrument is delivered with a factory calibrated gauge stable for at least one year (within 0.1%) when kept in its protective box.
vUV version
From January 2021, the vUV version of the CT7 is available, operating with detectors reaching wavelengths up to 308nm. The 7 bands can be chosen from 308 to 940nm. The standard wavelengths are as follows:
Wavelength (nm) |
Bandpass (nm) |
308 |
13 |
325 |
13 |
365 |
10 |
430 |
25 |
528 |
30 |
590 |
20 |
625 |
18 |
We were able to achieve an accuracy of measurement of the reflectivity and repeatability similar to the standard version of the CT7 on each wavelength down to 308nm and are very proud to present our new instrument to the astrophysical community.
NB: the two vUV channels (308nm and 325nm) do not detect the scattering (dust index) due to the weakness of the input signal.
IR version
In May 2024, we developed a new IR version of the CT7 that allows measuring with high precision 7 wavelengths up to 1050nm. The 7 bands can be chosen according to your needs, from 365 to 1050nm. The standard wavelengths are as follows:
Wavelength (nm) |
Bandpass (nm) |
405 |
15 |
470 |
30 |
590 |
20 |
730 |
50 |
850 |
50 |
940 |
40 |
1050 |
60 |
Having successfully overcome the technical challenge posed by the limited sensitivity range of the detectors, we have achieved a measurement accuracy equivalent to that of the classic CT7 at each wavelength up to 1050 nm.
Dust detector
The CT7 is also a scatterometer, which operates as dust detector. The latter measures the scattered light in the seven channels. It measures the integrated scattered light between 9° and 19°. This measurement yields a fair approximation for the value of the TIS. The dust index indicates the quantity of dust (in relative surface) covering the mirror.