thin-film polarizers (original) (raw)

Acronym: TFP

Definition: optical polarizers based on a multilayer dielectric coating

Category: general optics

• polarization optics
  • polarizers
    * sheet polarizers
    * wire grid polarizers
    * cube polarizers
    * thin-film polarizers

Related: polarizersdielectric coatings

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📦 For purchasing thin-film polarizers, use the RP Photonics Buyer's Guide — an expert-curated directory for finding all relevant suppliers, which also offers advanced purchasing assistance.

Contents

Operation Principle of Thin-film Polarizers

Thin-film polarizers are a kind of optical polarizers based on interference effects in a multilayer dielectric coating. That coating is usually placed on a glass plate. (A birefringent optical material as in various other types of polarizers is not needed.) A strongly polarization-dependent reflectivity is achieved for some range of incidence angles: Basically always, s-polarized light is reflected and p-polarized light transmitted. This strong polarization dependence results from polarization-dependent reflection and transmission coefficients at the interfaces between the layers.

It is often convenient to design a thin-film polarizer such that it can be operated with an incidence angle of 45°, such that the reflected beam is obtained with an angular change of 90°. However, other incidence angles are also common.

Kinds of Thin-film Polarizers

There are different kinds of thin-film polarizers concerning optical fabrication technology and various properties which are of practical interest:

• Plate polarizers (Figure 1) consist only of a coated glass plate. The design is often made such that the angle of incidence is essential at Brewster's angle. In that way, reflection losses for the transmitted light on the backside are avoided easily. For other angles of incidence such as 45° (which is often convenient), an anti-reflection coating is required on the backside, and the layer structure design for the front side can also be more difficult.

Figure 1: A plate polarizer for operation near Brewster's angle, having a reflecting coating on the top side and no coating on the bottom side.

• There are also polarizing cubes (Figure 2), which are obtained by coating the hypotenuse face of a 45° prism and cementing it to another 45° prism, forming a cube. The input and output faces usually obtain anti-reflection coatings.
• The basic idea of the common MacNeille cube design [2] is to eliminate the reflection for p polarization by having Brewster's angle at all internal interfaces. It is then easy to obtain high reflectivity for s polarization with a simple Bragg mirror design without introducing a significant reflection for p polarization. The Brewster angle condition requires that a substrate material with suitable refractive index (for given coating materials) is chosen. Such designs work well in a large range of wavelengths, but only in a narrow angular range (typically a few degrees).

In other polarizing cube designs than the MacNeille design, one does not fulfill the Brewster angle condition but uses interference effects to suppress reflection for p polarization. Such interference polarizers typically operate well only in narrow wavelength ranges but give more flexibility concerning the used materials.

The cemented interface of a polarizing cube leads to a lower optical damage threshold of the order of 1 J/cm2 for nanosecond laser pulses. Optically contacted epoxy-free polarizing cubes, not requiring a cement, can stand several times higher fluences.

Figure 2: A polarizing cube based on a thin-film coating between two 45° prisms.

Limited Spectral and Angular Ranges

Since the interference effects in the multilayer coating are wavelength-dependent, a thin-film polarizer can work only in a limited wavelength range and angular range. However, operation in a range of tens or even a few hundred nanometers is possible by proper optimization of the thin film design. Such broadband polarizers, however, do not achieve the very high performance of narrowband polarizers (laser line polarizers), which are optimized for a narrow wavelength range. Figure 3 shows an example with a moderate operation bandwidth of 50 nm.

Figure 3: Reflectivities of a thin-film polarizer cube based on TiO2/SiO2, designed for operation at 600–650 nm with the software RP Coating.

For the optimization of the coatings for thin-film polarizers, similar numerical techniques can be used as for designing broadband beam splitters or dichroic mirrors, for example.

An advantage of thin-film polarizers is that they can be made with rather large dimensions, which is more difficult with crystalline (birefringent) polarizers. It is thus possible to operate such high-power or high-energy devices with laser pulses at very high peak power levels.

Suppliers

Sponsored content: The RP Photonics Buyer's Guide contains 37 suppliers for thin-film polarizers. Among them:

⚙ hardware

LASEROPTIK offers various types of polarizers, including thin-film (TFP) devices, cube polarizers (CP) and broadband polarizers (BBPOL). We can work in different wavelength ranges from the mid-IR (2.1 μm) to the UV (157 nm).

⚙ hardware

Perkins Precision Developments (PPD) offers high-performance Brewster’s angle polarizers and 45-degree plate polarizers featuring easy alignment. Utilizing advanced Ion Beam Sputtering (IBS) coating technology, our dielectric thin film plate polarizers are environmentally stable, ensuring no spectral shift due to time, moisture, or temperature. The precision of IBS coatings guarantees high transmission at specific angles of incidence without the need for angle tuning.

PPD's IBS coated polarizing beam splitters are designed for low absorption and high extinction (Tp/Ts), with high damage thresholds suitable for high energy Nd:YAG and fiber lasers, as well as other high-power pulsed and CW laser systems in the visible and near-infrared spectrum.

⚙ hardware

Avantier is capable of delivering a broad range of coatings, including anti-reflective, high reflective, and partial reflective coatings. Our coating offerings vary from simple anti-reflective coatings to intricate multilayer dielectric stacks. Examples of dielectric coatings include BBAR, V-coatings, dual wavelength coatings, and filters with sharp cut-on and cut-off wavelengths.

⚙ hardware

EKSMA Optics has a wide range of BK7 and UV fused silica thin film laser polarizers for quick delivery. Thin film polarizers feature high laser damage thresholds and are designed for the most demanding applications with Nd host lasers operating in the 1040–1070 nm range and with femtosecond Ti:sapphire or Yb:KGW/KYW lasers.

⚙ hardware

Artifex Engineering offers custom dielectric thin-film polarizers with a high damage threshold. Our thin film polarizers are commonly used for Q-Switching and other high power applications. These components are dielectric coated glass substrates designed for use at the Brewster angle. Visit our product page for more information. We look forward to your inquiry.

⚙ hardware

OPTOMAN offers thin film polarizers, that are the optimal choice for polarizing high energy laser light. Thin film polarizers accomplish this task with a high efficiency level due to negligible absorption within the coating, transmittance (_T_p) higher than 99%, and reflectance (_R_s) as high as 99.99%.

OPTOMAN will provide an optimal solution in terms of extinction ratio (10'000:1 is possible), angle of incidence (various choices depending on application), and damage threshold (>49.4 J/cm2 @ 1064 nm, 10 ns, 100 Hz can be achieved in some configurations). Broadband configurations for femtosecond applications are also feasible.

Standard in-stock IBS coated polarizers can be found in OPTOSHOP.

⚙ hardware

Shanghai Optics can provide all types of anti-reflective, high reflective, and partial reflective coatings. We produce a wide variety of coatings from a single layer of anti-reflective coating to complex multilayer dielectric stacks. Types of dielectric coatings are BBAR, V-coatings, dual wavelength coatings, and sharp cut-on and cut-off filters.

⚙ hardware

Optogama’s high-contrast thin-film polarizers are engineered for performance in demanding laser environments.

Leveraging ion beam sputtered (IBS) coating technology, these polarizers deliver an exceptional extinction ratio (Tp:Ts > 1000:1), ensuring clean polarization separation even at high power densities. With outstanding surface quality and LIDT, they are built to thrive in both scientific-grade systems and industrial-class lasers.

Key advantages:

• Wavelength range: from deep UV at 230 nm to the near-IR at 2000 nm—these optics support a wide range of laser platforms.
• High-Power Ready: Optimized for high LIDT, they excel in environments with intense beam exposure.
• Scalable Design: Aperture sizes up to 160 mm accommodate large beam diameters without compromising uniformity.
• Custom Solutions: Tailored coatings, sizes, and mounts—engineered for integration into your unique optical path.

Bibliography

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