How to Choose a Beamsplitter or Fold Mirror for Your Interferometer
By Zygo | Published: 2026-10-29
Category: Buying Guides
Learn the key factors for selecting the right beamsplitter or fold mirror for your interferometer setup, including type, vacuum compatibility, and alignment needs.
Quick Answer
Choose a beamsplitter based on the required split ratio (e.g., 50/50 for equal intensity) or a fold mirror to redirect the beam without splitting. Select vacuum compatibility only if your setup operates in a vacuum chamber.
Beamsplitter Types and Their Applications
The type of beamsplitter you choose determines how laser light is divided between the reference and test paths in your interferometer. A 50/50 split is standard for most setups, while 33/67, 75/25, or 10/90 ratios are used when one path requires significantly more light, such as in low-reflectivity sample testing.
Fold Mirrors vs. Beamsplitters
A fold mirror reflects the entire beam without splitting it. Use a fold mirror when you need to route light around obstacles or adjust the optical path length without altering intensity. Beamsplitters are for splitting; fold mirrors are for redirecting.
Vacuum Compatibility Considerations
Standard beamsplitters and fold mirrors are designed for ambient air. If your interferometer operates inside a vacuum chamber, you must select the vacuum-compatible option to avoid outgassing or optical degradation. For typical lab use, standard is sufficient.
Decision Rules for Choosing
- 1. Determine Your Beam Routing Need: If you need to split the laser beam into two paths, choose a beamsplitter. If you need to redirect the entire beam without splitting, choose a fold mirror.
- 2. Select the Split Ratio: For most interferometry applications, a 50/50 split is ideal. Choose 33/67, 75/25, or 10/90 when one path needs more light, such as for measuring low-reflectivity surfaces. Check your interferometer's reference and test path requirements before selecting.
- 3. Decide on Vacuum Compatibility: Select 'Yes' for Vacuum Compatibility only if your interferometer operates in a vacuum chamber. For standard lab environments, choose 'No' (Standard).
Product Facts
- Beamsplitters & Fold Mirror: Zygo Beamsplitters & Fold Mirror optics are available in types: Fold Mirror, 50/50, 33/67, 75/25, and 10/90. This variety lets you match the split ratio to your specific measurement needs, whether equal intensity or uneven distribution.
Beamsplitters & Fold Mirror
Who Should Choose What
Best For
- Standard interferometer setups needing equal beam splitting
- Optical paths requiring beam redirection without intensity loss
Not For
- Setups requiring custom split ratios not listed (e.g., 20/80) – consider a variable beamsplitter instead
