Frequently Asked Questions
Below are some frequently asked questions and answers about laser optics, dielectric optical coatings, polarization and photonics in general. Please contact us for more details about our high-energy laser mirrors, epoxy-free polarizing beam splitter cubes, low-loss IBS coatings and low roughness super-polished substrates.
What are the advantages of IBS coatings over E-Beam, IAD and Magnetron coating methods?
Typical PPD 0° IBS AR Coating spec’d to R<0.05% per surface
Typical Absorption
Why is chemical bonding better than diffusion bonding and optical contacting?
PPD’s adhesive-free chemical bonding technology is a less extreme process than diffusion bonding, working at much lower temperatures and without pressure. This allows us to work with a wider range of materials and with our in-house IBS coatings integrated into the assembly. It is also more stable and durable than standard optical contacting, resulting in robust components that can be further polished and/or coated even after assembly.
In the past, some of our dielectric coatings have had performance changes during usage, as if their reflection curves spectrally shifted. Why did they do this, and will your ion-beam sputtered coatings do this too?
Environmental Stability of IBS Coatings
(Testing Courtesy of Raytheon Corporation)
What's a good way to split unpolarized light into two polarized parallel beams?
There are multiple ways to split unpolarized light into polarized parallel beams. If you have a low power application you could use a birefringent crystal (such as calcite) and a halfwaveplate. For higher powers, a simple solution would be to use a custom thin-film plate polarizer with a high-reflectivity coating on the back surface (see the figure). The thickness of the custom plate polarizer is specifically chosen to achieve the desired beam separation.
How does surface quality differ from RMS surface roughness?
The surface quality of an optical surface describes its cosmetic appearance and includes such defects as scratches, sleeks, chips, pits, or digs. These defects can result in an increase in scattered light, reduced system performance and even laser damage due to absorption at high power levels. The most common specification used for surface quality is the scratch-dig specification described by MIL-PRF-13830B. The scratch designation is determined by comparing the scratches or sleeks on a surface to a set of standard scratches per the MIL-Spec under controlled lighting conditions. The dig designation directly relates to the digs, or small pits in the surface as calculated at the diameter of the dig in microns divided by 10.
Surface roughness is a measure of high-frequency deviations in the departure of a surface from ideal using non-contact profilometry or white light interferometry. The root-mean-square (RMS) value indicates overall roughness and is based on the standard deviation of the surface height from the mean value (ymean) while peak-to-valley (PV) gives the maximum deviation at a single spot on the surface.
Typical surface roughness at PPD is < 5Å RMS, but we also offer super-polishing of plano and curved surfaces to as low at < 1Å RMS.
What is Brewster's Angle?
Brewster’s angle ƟB is the angle of incidence at which P-polarized light is perfectly transmitted with no reflection. This equation is known as Brewster’s law where ɳ1 is the refractive index of the incident medium and ɳ2 is the index of the transmitted medium.
Thin film Brewster plate polarizers utilize Brewster’s angle and multi-layer dielectric coatings to separate unpolarized light into its S and P polarization components with an extinction ratio (Tp/Ts) of greater than 1000:1 in the transmitted beam.
When does Total Internal Reflection occur?
Total internal reflection (TIR) takes place at the boundary between two transparent media when a ray of light in a medium of higher index of refraction (optically denser) approaches a second medium (with a lower refractive index, or optically rarer) at an angle of incidence greater than a certain limiting angle called the critical angle (ƟC). At all angles less than the critical angle, both refraction and reflection occur in varying proportions. For a water-air surface the critical angle is 48.5°.
The critical angle is given by ƟC = arcsin(ɳ2/ɳ1) , where ɳ2 is the index of the transmitted medium and ɳ1 is the refractive index of the incident medium. ɳ2 ≤ ɳ1 is required for TIR.
What is the best way to clean and handle laser optics?
If it’s not dirty, don’t clean it! Handling optics increases their chances of getting dirty or damaged, so optics should only be cleaned when there is a clear need to do so.
Handling should always take place in a clean-room environment where there are minimal particulates and airborne dust. To protect the surfaces of the optics from contamination, it is essential to wear gloves or finger cots that are powder-free and resistant to solvents such as acetone. Bare skin should never come into contact with any coated surface, as natural oils or debris from hands can stain coatings and/or contribute to long-term degradation. Similarly, lens tissue should only be used once and then discarded; reusing it can transfer contaminants back onto the optic and cause scratches. Given the cost of precision optical components, using a fresh lens tissue each time is a minor expense that helps prevent costly damage.
To determine whether an optic requires cleaning, it should be inspected carefully under a strong visible-light source. By holding the optic at different angles, one can more easily detect scattering caused by the presence of dust, streaks or stains.
1.Required Materials
Tweezers (2 pcs, for small optics)
Examination grade latex gloves
Methanol (analytical grade) or Chromatography grade acetone
Berkshire Pro JX wipes or lint free Q-tips for small optics
2. Procedure
Hold the mirror gently by the outer diameter, using tweezers for small optics.
Moisten a Berkshire Pro JX wipe with methanol.
Carefully wipe only 1/3 to 1/2 of the mirror surface: – Avoid contact with the bevel. – Apply minimal pressure to prevent linting or scratching.
Rotate the part using tweezers and repeat the wipe process until the full surface is clean.
Use a fresh wipe for each stroke to prevent contamination.
Inspect the part under proper (bright fiber) lighting for remaining particulates during and after cleaning.
What Polarizer should I use for my high power Nd:YAG laser?
Polarizers and polarizing beamspliters come in many forms, such as calcite crystal prisms and wire grid designs. However, not all types are suitable for high energy applications like Directed Energy and Aerospace.
In scenarios involving high-power laser systems or applications where both polarization components must be retained, and absorption minimized, polymer sheet polarizers, birefringent prism polarizers and wire grid polarizers are not ideal. In these cases, a polarization beamspliter is used to split the input beam into two beams with opposite polarizations, both of which can be used. The splittng can be done by reflection or refraction of one of the polarization states.
Click here for more information.
When should I clean my laser mirrors and beam splitters?
Photonics Spectra Digital Edition – December 2025 Photonic Fundamentals
Cleaning optical components is about more than maintaining aesthetics. In highprecision systems, particularly those involving lasers, even minor contamination of the optics can lead to component failure. While contaminants — either on a coating or at the interface with the substrate — can absorb laser energy and degrade the coating or substrate surface, the presence of dust, streaks, and/or stains scatters light, which reduces the overall functionality of the laser optic. Numerous studies have shown that the cleaning process alone can vary the laser damage threshold of a coated optic by as much as 75%.
Although standards across the photonics industry vary, the rule of “if it’s not dirty, don’t clean it” is widely accepted by the field. Optics are sensitive instruments, and since every interaction poses a risk of introducing damage or debris, they should be cleaned only when there is a clear need to do so. Unnecessary or aggressive cleaning can reduce the life of optical coatings, especially on highperformance components. To determine whether an optic requires cleaning, it should be carefully inspected using a strong visible light source. Holding the optic at different angles enables the person performing the inspection to more easily detect scattering caused by dust or residue.Handling comes with its own set of best practices. It should always take place in a cleanroom environment where particulates and airborne dust are at a minimum. Additionally, to protect the surfaces of the optics from contamination, it is essential to wear powder-free gloves or finger cots that are resistant to solvents such as acetone. Bare skin should never come into contact with any coated surface, because natural oils or debris from hands can stain coatings and contribute to long-term degradation.
Similarly, lens tissue should be used only once and then discarded. Reusing it can transfer contaminants back onto the optic and cause scratches. Given the cost of precision optical components, using a fresh lens tissue each time is a minor expense that helps prevent costly damage.
In addition to ensuring optimal optical performance, cleaning helps to prevent permanent damage to the component.
At the same time, the process of laser optics cleaning is multifaceted, requiring consideration of more than just the condition of the optic in question and the target application. Understanding a range of techniques, approaches to handling, and best practices for the many distinct optical materials in use today is essential to maintaining the superior performance of laser optics.
Why Choose Perkins?
- CMMC 2.0 Level 2 Self-Assessed
- Consistent Quality
- In-house Manufacturing & Coating
- Production Flexibility
- Reliable Customer Service
- Customer Focused Solutions
- R & D Projects Welcome
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Markets Served
- OEM Laser Manufacturing
- Semiconductor Test & Measurement
- Industrial Materials Processing
- Space-qualified Satellite Optics
- Universities/Academia/Research
- Biomedical Instrumentation
- Aerospace /Directed Energy
- Quantum Science
Corporate Memberships
Society of photo- Optical instrumentation Engineers
Colorado Photonics Industry Association
Optical Society of America
