10.01.2024

White Light Interferometer Measuring Station

MEASUREMENT OF THE SURFACE ROUGHNESS OF SUBSTRATES

In order to produce high-quality laser optics, substrates with good shape accuracy and polish quality are required. It is only possible to specify laser optics precisely using measurement options so that the customer can rely on consistent quality.

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Introduction

Beyond Borders

For laser applications, a shape accuracy of lambda/10 has proven to be useful, whereby the reference wavelength 546 nm is used. As a rule, a P4 polish (ultra-fine polish) with a cleanliness of 5/4 x 0.025 is also used for 1.0" diameter substrates. The micro-roughness of the surface also determines which scattering losses occur in mirrors or other optics.

For mirrors with very high reflectance values of R > 99.95 % or higher, the losses due to scattering and absorption must be correspondingly low. So-called "superpolished" substrates are generally used for such applications. These are characterised by a micro-roughness (RMS value) in the range < 0.1 nm. However, it is also important to control the roughness of the surface for other laser applications.

White light interferometry. A white light interferometer is available for such measurements. White light interferometry is a non-contact optical measurement method that utilises the interference of broadband light to measure the 3-dimensional structure of the surface. The measurement accuracy is < 0.1 nm for the vertical resolution.

Quality control. All lenses manufactured in-house at LASER COMPONENTS can be checked with this technology, just like externally manufactured substrates. For our customers, this extra quality control means that they can always be sure of receiving high-quality optics.
For applications where "superpolished" optics are required and if otherwise necessary, appropriate roughness documentation can be produced.

Exemplary Measurement Protocol

Determination of the roughness of a substrate

The upper part of the measurement protocol shows the substrate surface in 2 or 3 dimensions as a height profile. The results of this evaluation are summarised in a table below. The value PV indicates the maximum value for the height difference. The RMS value is assigned to the micro-roughness. A height profile can also be seen as a section in the centre.

We carry out these measurements on a random basis for all substrates. Such a measurement is always planned for special applications and documentation can be provided at the customer's request.
By measuring the micro-roughness of the substrate surfaces, we ensure that the quality of the optics we use is constant and very high.

WHAT PROOF OF QUALITY DO YOU NEED FOR LASER OPTICS?

Head of Business Unit Laser Optics

Barbara Herdt

LASER COMPONENTS Germany GmbH

82140 Olching

b.herdt(at)lasercomponents.com

T. +49 8142 2864-41

Products

Beyond Borders

Aspherical lenses correct aberrations, which in monochromatic light include image sharpness errors and distortion.

A typical application of these lenses is the focusing of a collimated beam onto an optical fiber.

Brewster plates are used to separate s- and p-polarized light.

Brewster plates have a rectangular shape and are inserted at a specific angle of incidence to the laser beam. Light that is polarized parallel to the plane of incidence/reflection is completely transmitted at Brewster’s angle, whereas about 50 % of s-polarized light is transmitted.

Cavity end mirrors are used to generate the laser beam in the resonator.

Resonator end mirrors, also known as cavity mirrors, are designed to have high reflectivity at the desired laser wavelength in order to maximize the efficiency of the laser.

ROUND AND RECTANGULAR CYCLINDER LENSES ARE USED TO CREATE LINES / BEAM EXPANSIONS IN ONE DIRECTION.

We offer plano-concave and plano-convex cyclindrical lenses in rectangular, square, and round form.

DIAGNOSTIC BEAM SPLITTERS FOR PROCESS MONITORING

Dichroic mirrors separate or combine two or more beams of different wavelengths in the desired ratio and enable process monitoring on the operating level in several wavelength ranges, as well as beam diagnostics. Their complex design enables multiple transmission and reflection ranges.

combine or separate two or more beams with different wavelengths.

Customized dichroic mirrors that are suitable for your individual application are manufactured upon request.

The degree of reflection slopes from the center of the optic in a Gaussian distribution.

Gaussion mirrors are used in unstable resonators - mostly as meniscus lenses with an integrated wedge to avoid back reflections despite of antireflection coatings.

Optimized for high-power lasers with intense pulse energies or high average powers

Mirrors for high-power lasers are high-precision optical components that direct or focus the laser beam. Thanks to a dielectric coating, the mirrors reflect the laser beam efficiently and withstand the high thermal load caused by the laser energy.

Protective windows are used during laser material processing to protect against material splashes.

Protective windows are the last optics to be used in front of the work area. They protect high-quality laser optics from material splashes during cutting, welding, drilling, structuring, marking and additive manufacturing. Protective windows are available in a variety of shapes and qualities.

FOR SPLITTING INTO ONE OR MORE DEFINED PARTIAL BEAMS.

When working with lasers, it is often necessary to split a laser beam into two or more defined partial beams. There are a variety of beam splitters for these applications, with different advantages and disadvantages. Dielectrically coated beam splitters have a high laser damage threshold.

Transmissive Plano-Parallel Plates WITH MINIMAL DISTORTION, SCATTERING OR ABSORPTION

Optical windows for laser applications are flat, transparent substrates made of materials with excellent optical properties. They are usually optimized to provide maximum transmission in a specific wavelength range providing low reflection and absorption at the same time.