Interferometric laser encoder detector heads
The Renishaw detector heads are part of the next-generation RLE laser encoder systems. They are the core of the optical measuring system, containing interferometer optics, an innovative multi‑channel fringe detection system and beam steering mechanisms.
Detector heads for high-throughput motion control applications
The detector heads are used with either an RLU100, RLU200 or RLU300 laser unit. Renishaw offers two detector head configurations:
DI differential interferometer detector heads
DI heads feature a dual beam interferometer which detects differential displacement between two remotely mounted mirrors, or measures changes in mirror angle. They are used in demanding applications, often within a vacuum environment, such as motion control of semiconductor wafer stages within electron-beam systems,
PMI plane mirror interferometer detector heads
PMI detector heads measure the displacement of a moving mirror relative to an integral fixed-length reference beam within the head. They are ideal for direct measurement of precision motion near the point-of-interest, eliminating Abbe error in applications such as high-performance XY stages. Within the PMI range, the choice of RP0 head (0° beam output orientation) and RP9 head (90° beam output orientation) offers design flexibility for a range of motion applications.
Benefits of the detector heads
Both Renishaw detector head configurations offer a range of features and benefits:
- Plug and play: No manual set-up is required to use any combination of compatible detector heads and laser units.
- Enhanced beam pointing stability: An innovative collimator locking mechanism isolates the optical components from mechanical loads on the fibre-optic cable.
- Cutting-edge performance: DI detector heads combine low power dissipation with high bandwidth and high stability. These can be used at a range of motion velocities without compromising static position stability.
- Simple installation: Individual optomechanical beam steerers are provided to align the DI detector head. This ensures that the RLE interferometer system can be quickly and easily installed onto the host machine. A single tool (2.5 mm hex key) is used for all head installation and beam alignment operations.
- Wide operating range: Optical and electronic subsystems in the detector heads and laser units maintain accuracy across a wide range of distances, mirror angles, and signal levels.
- Robust optical immunity: The interferometers used in the detector heads include components for resistance to back reflections.
- Simple cleanroom preparation: The detector heads are designed to be easily cleaned, simplifying the process of preparing the heads for use in cleanroom environments.
Compactness: The PMI detector head is small and only requires a single target mirror, ensuring easy integration into a wide range of applications.
Differential measurement: In wafer inspection applications, DI heads can measure the position of the SEM column relative to the wafer stage. This eliminates common mode errors, such as motion of the vacuum chamber side wall associated with environmental fluctuations.
Technical specifications
| Specifications | DI differential and PMI plane mirror detector heads |
| Maximum motion velocity |
1.0 m/s |
| Sub-Divisional Error (SDE) | < ±1 nm at velocities up to 0.2 m/s without automatic SDE correction This can be further reduced by automatic SDE correction on the RLU200 and RLU300 |
Electronic noise | < 10 pm, 1 Hz to 50 kHz band < 200 pm, 1 Hz to 25 MHz band |
| Measurement range | 2 m ±400 µrad @ 1m head-mirror separation |
| Power dissipation | 0.14 W |
Downloads: datasheets and technical documents
Further information about the technical specifications of the Renishaw laser encoder products, such as datasheets and installation guides, are available from our technical downloads section.
Discover our range of interferometric laser encoders designed to meet your high-accuracy motion control needs.