Brewster windows generate high-purity linearly polarized light in laser cavities.
P-Polarized Light is Transmitted with almost Zero Reflection Losses.
Laser garde UV Fused Silica.
Brewster windows are base on Fresnel's law and Various sizes available.
At an orientation of 55.57°, the object has a circular profile.
Brewster Window Mounts Available.
Brewster's law, named after the Scottish physicist Sir David Brewster, deals with the behavior of light when it encounters a dielectric surface (a non-conducting medium like glass or plastic). When unpolarized light (light with vibrations in all possible directions) is incident on a dielectric surface, a portion of it is reflected and a portion is transmitted through the surface.Brewster windows generate high-purity linearly polarized light in laser cavities.P-Polarized Light is Transmitted with almost Zero Reflection Losses.The mathematical expression for the Brewster angle (θ_B) is given by: θ_B = arctan(n), where "n" represents the refractive index of the dielectric medium.
Fig 1：Brewster window light path diagram
CRYSMIT's Brewster Windows are specifically designed to have a circular profile when positioned at Brewster's angle (55.57°). These windows offer laser-grade surface quality, exceptional parallelism, and minimal wavefront distortion (λ/10). By using them at 55.57°, they enable the transmission of the p-polarized component without any reflection losses while introducing losses for the s-polarized component. They are ideal for laser cavity applications and the production of linearly polarized light.
Fig 2 ：CRYSMIT's Brewster Windows in laser cavity applications.
An illustrative instance of a Brewster's window is exemplified by a helium-neon laser equipped with a hermetically sealed glass tube and an external resonator containing mirrors. The gas mixture is shielded from the surrounding atmosphere by the glass windows. When taking into account the minor output coupler transmission and limited gain, the losses occurring at these interfaces are less than 1% per pass.
Typically, an uncoated glass plate reflects a few percent of incident light when it strikes the surface at a right angle. However, through the implementation of an anti-reflection coating, this percentage can be diminished to as little as 0.2%. Brewster windows, in comparison, exhibit losses that are more than 10 times lower.
| Material | N-BK7, UVFS |
| Axis tolerance(mm) | +0/-0.1 |
| Thickness tolerance(mm) | ±0.1 |
| Surface quality | 20/10 per MIL-PRT-13830B |
| Wavefront distortion | λ/10 @ 633 nm |
| Clear aperture | 90% of diameter |
| Parallelism | < 10 arcsec |
What is the functional relationship between reflectance of Fused Silica(Uncoated) for polarized light and angle of incidence？
Fig 1: The picture above shows the reflectance for P-polarized light goes to zero at Brewster's angle (55.57°@632.8nm).
What is the functional relationship between reflectance of N-BK7(Uncoated) for polarized light and angle of incidence？
Fig 2 : The picture above shows the reflectance for P-polarized light goes to zero at Brewster's angle (56.57°@632.8nm).
Fig 3 : This chart above shows the calculated value of Brewster's angle as a function of wavelength when light is passing from air to Fused Silica.
Fig 4 : This chart above shows the calculated value of Brewster's angle as a function of wavelength when light is passing from air to N-BK7.
How does Brewster Window work in a Laser Cavity ？
In some He-Ne lasers, a single Brewster window is used instead of internal mirrors. By positioning the laser light at Brewster's angle, the resulting light becomes completely polarized.
One common example of a Brewster window application is the helium-neon laser, which consists of a sealed glass tube and an external resonator with mirrors. The glass windows act as a barrier between the gas mixture and the surrounding air. With careful consideration of low output coupler transmission and small gain, the losses at these interfaces are kept below 1% per pass.
The advantage of using a Brewster window is that any residual reflection will exit the resonator rather than causing interference effects. This allows for the forced polarization of the laser emission along the p-direction, as there is a difference in loss between s and p polarization. In most lasers, the polarization direction is determined by this effect.
The main functions of Brewster windows include: Production of linearly polarized radiation within a laser cavities and Avoidance of laser damage caused by back-reflected radiation in highly reflective metals.
Literature
In taking into consideration the distinct properties displayed by different birefringent crystals and the variations in structure among different types of polarizers，Our " Polarizer Guide " is designed to help you make an informed choice when selecting polarizers.
Brewster window and windowless resonant spectrophones for intracavity operation R Gerlach, NM Amer - Applied physics, 1980 - Springer
Design and measurement of a W-band Brewster window; Y Zhang, L Zhang, 2015 - ieeexplore.ieee.org
