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Otto Pregizer Optik

 

The COATEST 7L apparatus

 
This instrument is the outcome of 50-year experience in optical metrology. I am a retired astronomer and I do not need building and selling instruments, but I care very much providing astronomers, my fellows, with quality control instruments that match the quality of modern telescopes.

 

History
The first IRIS was build 15 years ago for checking the quality of car windshields in Sweden. It was originally a scatterometer. Winters are hard up there and they use nailed tires so that at the end of winter, most windshields are like sand blasted. The governmental road security organization asked me to develop a handy instrument for checking the quality of windshield in the field. Soon, a reflectometer was added to the same instrument and it became quite sophisticated, including four wave bands as it was provided to major observatories.
Today, this instrument looks to me like a dinosaur; with my accumulated experience and the many discussions I had with astronomers, I am able today to propose what I think is the best up to date instrument for observatories. The electronic is based on a TI DSP board and will be up to date for years. Light sources are SM LED's associated with fiber optics; LED's can be easily upgraded if new wave bands are demanded.

 

Specifications

The COATEST 7L is a new instrument specially thought for accurate long term assesment of the mirrors coating.
It has an acceptance angle of 1.5° (half angle) and works at 8° incidence.

The seven Bands are chosen to be equidistant on the energy scale.

Wavelength (nm) Bandpass (nm)
365 10
405 15
465 20
520 30
630 30
760 50
970 40

The sources are modulated at a frequency around 5Khz and detected by the technique of digital lock in amplifier based on a DSP board.

Two identical detectors are used; one to measure the reference signal of the source, the other to measure the reflected signal. Both signals are digitaly 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 insures a long term absolute stability and total immunity against temperature variations even when the sources degrade or vary in intensity. This instrument is factory calibrated once for all. Only dirt or pollution on internal optical elements could change the response and necessitate recalibration.
  • Global absolute accuracy : 0.3% (405, 465, 520 and 630 nm); 0.5% (365, 760 and 970 nm) for R>50%
  • Repeatability: 0.01% for R>50% (0.2% for 970 nm)
The apparatus is small (80 mm x 60 mm x 120 mm high) and light (<500 gr) and in one piece (no wire; one hand operation).
It is positionned by a three point soft contact. Curved mirrors can be measured without correction down to a radius of + or – 1 m.
Internal memory keeps more than 200 measurements including date, time and temperature, sequential number and individual identification. Talking with the apparatus via a dedicated console on a PC through an USB2 connection.
Batteries are charged while connected to the USB port of the PC. They last for more than 200 measurements and four hours when CT7 is on; one week when CT7 is asleep. Independant USB loader can also be utilized; full charge takes about three hours.

 

Dust detector

The Coatest 7L can be equipped with a dust detector. The latter measures the scattered light in red light (630 nm), in green light (530 nm), and possibly in UV light (365 nm). It measures the integrated scattered light between 9° and 19°. This measurement yields a fair approximation for the relative value of the TIS for the local type of dust at the site. The dust index indicates the quantity of dust (in relative surface) covering the mirror.

 

VW calibration setup

Although the Coatest 7L does not need recalibration unless it has been polluted, we have designed a VW jig that fits on the instrument and yields the absolute values of reflectivity of a gauge in the seven bands; this gauge can then be used immediately after calibration to check the  Coatest 7L  and readjust its software parameters.

This jig is a precision instrument with very accurate motions of an auxiliary mirror in order that the beams in the V configuration has exactly the same path as the beam in the W configuration except for two reflections on the unknown gauge. This is developed and explained in Application Note #8.  

 

CT1 Windshield SLI measurement

CT1 is based on the CT7 design and includes all the features that yields the outstanding repeatability and accuracy of this instrument.

It measures the TIS (total integrated scattering) and the SLI (scattered light index) of the exposed automotive windscreen for security control from outside the car.

The measuring spot is 6 times larger than the spot used by the IRIS SC instrument, and the light source is close to illuminant A. It is completely immune against external lighting andaccurate measurements can be performed in full sun light.

The instrument is provided with an elaborate software that allows identification of car, date time and temperature attached to each measurement and retrieval and processing of the measurements on a PC.

 

Other instruments

 

Roughness meter

This instrument measures the reflectivity of the sample at grazing incidence utilizing the seven wavelength bands of CT7. It is based on the same principle of digital lock-in detection, inheriting of the extreme stability of this process.

The instrument yields the roughness of surfaces in the range of 1 µm up to 500 µm.  

It has the same general structure and ease of use than the CT7.  

 

Solar Plant Mirror Meter
(Second surface reflectometer)

This is a low cost simplified version of the CT7.

It is specially designed for helping the maintenance of solar furnace mirrors. It measures the total reflective efficiency of second surface mirrors as weighted by the solar power spectrum.

This is achieved by utilizing two large wavelength bands covering each approximately 50% of the solar energy, and averaging the reflectivity in the two bands. One band covers the visible radiation from 370 nm up to 720 nm, while the other covers the IR part of the spectrum from 720 nm up to 2 µm.

It also has the same general structure as CT7 and is specially fit for measuring cylindrical mirrors.  

 

Additional options:

A built-in GPS receiver for time and location-stamping of the measurements.