Measuring methods for laser optics
LASEROPTIK has more than 40 years of experience with high quality coatings. During these years we collected valuable knowledge about the properties of our optics from the best laboratories we could find: the experiences and feedbacks of our customers.
Additionally, we developed new coating techniques, measurement devices and improved coating materials in co-operation with research partners like Laser Zentrum Hannover e.V. (LZH), Fraunhofer Institute for Applied Optics and Precision Engineering (IOF) in Jena or Institut für Nanophotonik Göttingen e.V. (IFNANO, formerly LLG).
To guarantee stable high quality of our optics LASEROPTIK owns a wide range of measuring equipment:
Optical surface inspection
Uncoated and coated optics are inspected with standard OLYMPUS microscopes, ZEISS differential interference contrast microscopes and for larger surfaces with a Keyence flexible microscope. For automated surface characterization we use an Argos 200.
Zeiss differential interference contrast microscope
Argos 200
Keyence flexible microscope
Surface roughness
For the production of low loss components it is necessary to quantify the surface roughness. This rms-value is measured by a Zygo NewView 9000 white light interferometer. The measuring sensitivity goes below 0.1 nm rms.
Zygo NewView 9000
Thin film stress
For many applications it is important to know exactly the thin film stress, respectively to compensate for the bending of the optics due to this stress. LASEROPTIK uses an in-situ stress measurement system and interferometric measurements for the quantification of the induced stress.
Focal length and wedge
Optical standard parameters like effective focal length (EFL), back focal length (BFL), radius of curvature or centering errors are inspected using an OptiSpheric®. Radii of 5 mm up to 500 mm and centering errors in the range of 10” to 5’ can be detected. Additionally it is possible to measure wedges from 10” to 1.5°.
OptiSpheric 1000 AF
Flatness
To check the accuracy of the surface, we use an interferometer with a measuring wavelength of 632.8 nm and a Zygo Verifire MST with a measuring wavelength of 1053 nm. 12" is possible as the maximum aperture. These devices can measure flatness up to λ/20 at room temperature. The flatness can be measured in transmission and reflection according to ISO 10110.
Zygo Verifire MST
Interferometer for smaller optics
Reflectance and transmittance
The most important quality tool in optical thin film production is the spectrophotometer. LASEROPTIK uses different types to measure transmittance respectively reflectance from vacuum-UV (120 nm) to infrared up to 50 μm. Besides a VUV-spectrometer built by LZH we mainly use PERKIN-ELMER spectrometers (Lambda 19/883/900/950/1050/ Frontier Optica). To give the coating engineers always a prompt access to a spectrometer for getting a fast feedback on the current production processes we provide one spectrometer for every two coating machines.
PERKIN-ELMER spectrometers
Micro-spot reflectance
Some substrates are challenging to analyze using classical spectrophotometers. They may be of small size (microlenses) or are strongly curved (fibers or ball lenses). Using Filmetrics® F40 we can record spectral curves in wavelength range of 400-1700 nm on a spot size of Ø 17 µm.
Filmetrics® F40 spectrometer
Group delay (GD) and group delay dispersion (GDD)
For ultrafast optics used with femtosecond pulsed lasers, the control of the phase respectively the group delay and group delay dispersion of the coatings is of great importance. We employ a custom built white-light interferometer as well as commercial systems to benefit from a wide range of dispersion measurements covering the UV up to the mid infrared.
Measurements can be performed in a wavelength range from 350–2400 nm, with an angle of incidence 0–60° and for both polarizations simultaneously. It is possible to measure single mirrors as well as mirror pairs.
Custom-built white-light interferometer
Cavity ring-down (CRD)
The accuracy of reflectance measurements with spectrophotometers is limited. Therefore, a cavity ring-down setup is employed to measure high reflectance for the wavelengths 635 nm and 1064 nm.
By analyzing the power decay in the cavity, reflectance can be measured in a range from 99.5 to 99.999%. Typical application examples for cavity ring-down measurement are low-loss mirrors.
Cavity ring-down setup
Environmental testing
A climate chamber and other equipment (e.g. abrasion-test-set) for environmental testing enable us to deliver optics fully certified for customer applications according to MIL and ISO standards.
Climate chamber and abrasion-test-set
Scattering
Forward and backward scattering can be detected in the wavelength range from 190–800 nm by a custom-made measuring device based on a Coblentz sphere. We also offer external qualifications at the IOF or LZH.
Absorption and laser induced damage threshold (LIDT)
Absorption measurements allow us to constantly verify and improve the quality of our coatings. Our in-house measurement capabilities cover the irradiation wavelengths 308 nm, 355 nm, 532 nm and 1064 nm.
A novel measurement set-up for a fully automated in-house LIDT testing according to ISO standard will be available at LASEROPTIK in 2025 (wavelengths: 1 micron and harmonics).
Moreover, LASEROPTIK benefits from a long-standing cooperation with domestic and international partners for characterizing optical components. The most important measurements are laser damage threshold (LIDT according to ISO 21254), optical losses, i.e. absorptance (ISO 11551) and scattering (ISO 13696).
Absorption measurement
To produce high power optics you have to consider the different mechanisms of laser induced damages and the influences of the substrates and coating materials. Therefore we would like to provide some background information on topic Laser Induced Damage Threshold (LIDT).
smartLIDT
Development of an AI-supported measuring stand for the fully automated determination of the laser damage threshold of high-power laser optics. smartLIDT »
Frequently asked questions
Can LASEROPTIK measure the spectral properties of optics?
Yes, with our many spectrometers (including one VUV- and two IR-spectrometers) we can measure transmittance and reflectance from 120 nm to 50 µm.
With a Cavity Ring Down setup (CRD) we can measure low-loss mirrors for 635 nm and 1064 nm.
Group Delay (GD) and Group Delay Dispersion (GDD) can be measured with our two white light interferometers.
Can LASEROPTIK measure the surface shape and roughness of substrates?
Yes, with our wide range of in-house measurement equipment, like autocollimators and different interferometers, we can measure radius of curvature, focal length, wedge angle, centering, surface roughness and flatness.
Additional measurements for special needs can be offered in co-operation with our research partners.
Can LASEROPTIK measure the number and size of defects of optics?
Yes, with our many microscopes, we can measure defects with a resolution of down to 1 μm. We also have a fully automatic defect scanner (ARGOS).
Can LASEROPTIK measure the lifetime and losses of optics?
We can do absorption measurements for the wavelengths 308 nm, 355 nm, 532 nm and 1064 nm on our own. Environmental testing can be done within our climate chamber.
Additional measurements for special needs can be offered in co-operation with our research partners.
Customized product qualification
We develop and offer customized solutions for the verification of product specifications and further demands.
