WaveMe includes two wavefront metrology modules. One is a Shack-Hartmann wavefront sensor, the other supports phase-shifting interferometry.
The Shack-Hartmann module can be adapted to other sensors for OEM applications. The sensor currently available is uses a Basler acA2500-60um or acA2500-20gm cameras (USB3 or GigE interfaces).
Specifications
| Sensor Resolution | 2592 x 2048 (ONSEMI Python 5000) |
| Wavefront Sampling Density | 150 micrometer |
| Wavefront Accuracy | 15 nm RMS (unaligned +/- 6 degrees) |
| Wavefront Accuracy | 10 nm RMS (aligned at minimum distance) |
| Wavelength | 405 nm |
| Min Source Distance | 25 cm |
| Interfaces | Ethernet (PoE)/ USB3 |
| Frame Rates | 20/Ethernet, 60/USB3 (Frames per second) |
Since Basler does not display the correct sensor in its product links, the acA2500-60um is shown below. Visually, it is identical to the acA2500-20gm (the GigE variant).
Our Shack-Hartmann module features a fused silica 150μm pitch lens array with chrome apertures. The hardware and software package is priced at 2,400 EUR, which includes one year of support.
Hardware requirements:
Currently, the Shack-Hartmann sensor is available for customer projects. A version available for direct order from our website is in development. Current delivery time: 3 weeks.
For inquiries, email contact@senslogic.de.
The performance of the phase-shifting module depends entirely on the optical design of the interferometer. For a Twyman-Green setup, accuracy will depend on many things. Most importantly, a phase-shifting setup requires two-beam interference. With a little care, this can of course be arranged but can never be assumed. Then, the planarity of the reference mirror and (perhaps related to the two-beam interference assumption), the amount of scattering from sub-surface polishing defects. There are obviously other contributions, but those can be controlled during the measurement itself.
When configured as a point diffraction interferometer (with phase-shifting), one mostly has to make sure that the reference pinhole is small enough and illuminated with a sufficiently small amount of coma. More details about the design can be found in the tech-talk about how to design a point-diffraction interferometer. a PS-PDI is usually used for diffraction-limited optical systems where it will typically reach 1/250, or better, of the wavelength used. This will depend on the choice of actuator but today, that is almost never an issue.
The phase-shifting implementation relies on precise synchronization between the camera and actuator to ensure a continuous flow of image data. The camera operates in streaming mode, with preparations for capturing the next interferogram occurring during the image download of the previous one.
This module can interact with an optional control module, allowing users to integrate their own libraries for interfacing with additional hardware. The library must implement only three functions: open, close, and set. The control module waits for the set function to complete, with no further synchronization required.
The primary application of PS-PDI with the control module is the calibration of MEMS devices and deformable mirrors. To keep pace with the rapid generation of wrapped wavefronts during interferogram capture, PS-PDI includes a fast phase un-wrapper.
The phase-shifting module needs accurate actuators to work properly, and luckily, there are plenty of suppliers out there. The tricky part? Most actuators we know of require that we ask for current position (polling), which might not sound like a big deal—unless you care about speed, like we do. Plus, these actuators need some software tuning depending on the load they’re handling.
There’s no universal software interface for actuators (like GenICam for vision cameras), so WaveMe accesses actuators through an abstraction layer that helps us quickly add new actuators when needed. Right now, we support actuators from PI, MCL, and Aerotech. And if you need a new API? No worries—that’s included, along with the tuning. You will need to send the actuator to Senslogic. We make sure everything works and send it back.