ZYGO Fizeau interferometer

Determination of optical properties of corner cubes

Pyramid, also known as (retroreflective mirror), is composed of three perpendicular planes which are perpendicular to each other. Regardless of the incident angle, the incident light is totally reflected on the three right-angle planes. The reflected light is always parallel to the incident light and returns 180 degrees. This is a very useful optical characteristic.

ZYGO Fizeau laser interferometer can be used to accurately measure the optical performance of the pyramid prism, such as three right-angle planes, the angle error between two pairs; and the angle difference between the reflected beam and the incident beam on the six sectors, as shown below.

Double Pass & Single Pass

It is similar to the right-angle prism that uses a Fizeau laser interferometer. The accuracy of measuring the pyramid is also divided into single pass and double pass, as shown below.

When passing the test in a double pass, half of the test beam needs to be shielded. In this way, the test light passes through the pyramid prism and is reflected on the standard surface of the half-shielded standard mirror; then it returns to the original path and then returns to the interferometer through the pyramid fold to interfere with the reference light. The test laser passes through the prism under test twice, the angle error is doubled, and the test resolution is higher.

When passing the test in a single pass, there is no need to block the test beam. Part of the fan test light passes through the right-angle prism and returns to the interferometer to interfere with the reference light of the corresponding fan part. The test laser passes the measured cone only once.

Test conditions and settings

On the pyramid measuring hardware, in addition to the main unit of the Fizeau interferometer, a flat standard mirror is needed, which is used to hold the two-dimensional adjustment frame of the pyramid and the three-claw from the center.

If the single-pass mode is used, a high-reflective Dynaflect standard mirror or an attenuator placed in the optical path is also required. For double passing, you also need to make a beam shielding board with A4 paper. The optical path is shown below.

Test procedure

In the Mx software, select the test type as Corner Cube measurement.

• If the pyramid is a transmission design, you need to enter the refractive index of the pyramid optical material; if the pyramid is a reflection design, enter the refractive index of the ambient air.

• After installing and calibrating the plane standard mirror; clamp the pyramid on the three-jaws of the two-dimensional adjustment frame, align the plane of the pyramid with the test beam, and place it as shown above.

• If it is a single-pass measurement, you need to place an attenuator in the optical path or use a Dynaflect high-reflective standard mirror.

• Adjust the optical zoom so that the stripes fill the field of view as much as possible.

• Rotate and adjust the pyramid device to make a certain boundary in the fringe diagram "vertical".

• Double-pass: Insert the beam shielding plate, adjust the position just along the "vertical" dividing line, and shield half of the beam.

• Double pass: Adjust the tilt of the standard mirror as close as possible to the zero fringe.

• Adjust the Focus of the interferometer so that the boundary of the fringe area is clear and sharp.

• Horizontal calibration.

• Take measurements.