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Frequently Asked Questions

What’s an inexpensive way to split unpolarized light into two polarized parallel beams? We need the beams to be separated by 1.7 mm and we’re operating at 810 nm, 200 W peak power in a 20-ms pulse duration. Our beam is approximately 0.8 mm by 15 mm.

There are a few ways you can achieve what you want. If you had a smaller beam size and lower optical powers, you could use a birefringent crystal (such as YVO4 or calcite) and a half-waveplate. With the higher powers and larger beam size in your application, an expensive but effective design is to use a polarizing beam splitter that splits the two beams into two orthogonal directions, then a right-angle prism to orient them parallel to each other. We suggest a simpler, more elegant design as shown below. It consists of a custom thin-film plate polarizer with a high-reflectivity coating on the back surface (see the figure). The thickness of the plate polarizer is specifically chosen so that the beams will be separated by 1.7 mm. One of the nice benefits of this design is that it uses only a single optical element

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What are the advantages of IBS coatings over E-Beam, IAD and Magnetron coating methods?

  • Higher damage thresholds ( > 40J/cm2 at 1064nm)
  • Tighter tolerances:
    • – AR < 0.05% for single wavelength
    • – HR > 99.995%
  • Spectrally stable (no moisture shifts)
  • Excellent durability and adhesion
  • Low loss (Absorption < 2ppm)
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Why dielectric coatings instead of metal?

Metal mirrors have long been the standard for general-purpose broadband high reflectors, but they have several significant limitations which make them a poor match for many of today’s laser applications. Although inexpensive upfront, drawbacks of metal mirrors include susceptibility to both laser damage and mechanical abrasions, tarnishing or surface degradation, and poor adhesion. Over the lifetime of an optic or optical system, increased reflectivity and durability could result in improved performance and cost savings.

PPC’s broadband dielectric ion beam sputtering (IBS) coating covers a broad wavelength range (350–1100 nm) with >99% reflectivity, independent of both angle and polarization. Our high-energy ion-beam-sputtering (IBS) process results in durable, dense dielectric films that have superior reflective and mechanical properties in addition to being easy to clean, scratch resistant and insensitive to environmental changes. With high damage thresholds and low scatter and absorption coefficients, they are ideal for frequency doubled and tripled Nd: YAG lasers, fiber lasers and broadband or tunable laser applications.

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What materials are available for your composite laser optics?

Fused silica, N-BK7
Zerodur, ULE
YAG (doped and undoped, crystalline and ceramic)
Spinel/Co:Spinel (crystalline and ceramic)

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Why is CADB® better than diffusion bonding and optical contacting?

The PPC CADB optical bonding technology is a “gentler” process than traditional diffusion bonding, working at much lower temperatures and without pressure. This allows us to offer solid state laser configurations with a much wider range of materials and with unique IBS coatings integrated into the assembly. Because of the proprietary chemical processing of the surfaces, it is also much more durable than standard optical contacting, resulting in robust, stable components that can be further polished or coated even after assembly.

In the past, we’ve had problems where the optical properties of our dielectric coatings changed when we put them under vacuum or in a dry nitrogen environment. Their transmission or reflection curves spectrally shifted leaving us with less than optimal conditions. Why did they do this, and will your ion-beam-sputtered coatings do this also?

The problem you are seeing is due to humidity effects. Water molecules are absorbed into the coatings, causing the coatings to swell, thus changing their optical thickness and the optical properties of the dielectric thin films. This typically only occurs if your supplier is using an evaporation process (E-beam) for depositing your coatings. ATF uses ion-beam sputtering (IBS) to deposit our coatings. The IBS process actually forms covalent bonds resulting in a packing density so tight and uniform that the water cannot be absorbed. Thus, IBS films exhibit exceptional environmental stability, and you won’t see any shifting under vacuum or in a dry nitrogen environment. IBS films also offer several other advantages including: lower scatter and absorption losses, fewer pin-hole defects, high laser damage thresholds, chemical resistance, and superior adhesion.

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