Variable Beam Splitter: Precision Control by The Principle of Polarization Application Note

Precision laser applications require fine power control. A variable beam splitter with a large dynamic range and precision control is designed to fulfill this purpose. It is suitable for intensity splitting between two polarization states over a wavelength range from UV to IR.

Operation Principle

This variable beam splitter consists of a specially designed precision optomechanical holder. The key optics involved include a half-wave plate and polarization beam splitter (PBS). The half-wave plate is usually made of birefringent crystal cut parallel to the optical axis. It is used to change the polarization direction of the incident beam. The surfaces of the waveplate and the beamsplitter cube are coated with an AR-coating over the designed wavelength range. The PBS placed after the half-wave plate reflects s-polarized light while transmitting p-polarized light. The intensity ratio of s-polarized to p-polarized beams may be continuously varied by rotating the wave plate. The intensity of either the exit beam or their intensity ratio can be controlled over a wide dynamic range. P-polarization can be selected for maximum transmission. A full range of intensity variation between the two beams from maximum to minimum can be achieved by rotating the half-wave plate from 0 to 45 degrees.

Variable Beam Splitter 1
Figure 1. Principle of the variable beam splitter
Variable Beam Splitter 3
Figure 2. The layout of the variable beam splitter

The key specifications of the variable beam splitters at different operating wavelengths are listed below.

Wavelength355/532/1064nm
TypeTransmission Mode
Clear Aperture14mm
Beam Shift0.5mm
Extinction Ratio>200:1
Power Variation Range0.5% – 95%
Damage Threshold>5J/cm2@1064nm, 20ns, 20Hz
Weight<300g
Table 1. Key specifications of polarization attenuator

Applications

The following listed characteristics enable the variable beam splitter to precisely control the laser intensity with fine adjustment steps. Using a suitable type of polarizer, this principle can be realized at very high-power levels.

  • Divides laser beam into two parallel beams of the manually adjustable intensity ratio
  • Large dynamic range
  • Negligible transmitted beam deviation
  • High optical damage threshold
  • Transmission attenuation range 0.5% – 95.0%
Variable Beam Splitter 5
Figure 3. Varieties of polarization laser optics

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