For wavefront detection of grating devices, have you tried the FIS4-NIR wavefront sensor?

Grating devices are key components in fields such as spectrometers, laser beam combining, and optical communication, and their beam splitting wavefront quality directly determines the performance of the devices. However, measuring 0th-order, ±1st-order multilevel, and multi-position transmission wavefront distortions has always been a challenge in the industry - traditional methods rely on complex optical path switching or repeated disassembly and assembly of sensors, which are inefficient and difficult to align.

In April 2026, engineers utilized the FIS4-NIR near-infrared wavefront sensor (operating wavelength 1064nm) to systematically conduct transmission wavefront testing on the 0th and ±1st order beam split spots of two grating samples, covering an area with a diameter of approximately 10.6mm at the center of the samples. Multiple positions on the left, middle, and right sides of each beam were tested individually.

Figure 1 Detection Optical Path Diagram

The limitations of traditional technological paths

Common transmission wavefront measurement methods include Twyman-Green interferometry, Fizeau interferometry, point diffraction interferometry, and Shack-Hartmann wavefront sensing. Traditional interferometry has high accuracy, but it relies on reference mirrors and strict vibration isolation, with complex optical paths and repeated adjustments for measuring different diffraction orders, making alignment difficult. Shack-Hartmann sensors have low spatial resolution and limited local distortion signals. Conventional instruments are difficult to complete full-field testing without changing the optical path.

Technical path and advantages of FIS4-NIR

The FIS4-NIR near-infrared wavefront sensor, based on four-wavefront lateral shearing interferometry technology, can simultaneously obtain shear interferograms in the X and Y directions with a single acquisition, and reconstruct the complete wavefront through Fourier algorithm. The sensor utilizes a combination of randomly encoded hybrid gratings and an infrared camera, with interference on the back-end image plane. It has low requirements for light source coherence, eliminates the need for phase shifting and deliberate search for specific imaging distances, and achieves nm-level accuracy interferometry with ordinary imaging systems. It features ultra-high vibration resistance and stability, enabling nm-level accuracy measurement without the need for vibration isolation.

Test purpose and experimental method

Experimental system: 1064nm laser + collimation and beam expansion module + FIS4-NIR wavefront sensor + grating to be tested.

Using the relative measurement method: First, collect the background of the cavity. Then, separately collect the interferograms of the 0th order and ±1st order transmitted light spots. After background subtraction processing, the true wavefront is obtained.

Figure 2 Schematic diagram of detection area

Main measurement results

Grating Sample No. 1: The three-dimensional and contour maps of wavefront distortion in the left, middle, and right areas of the 0-level beam are shown below:

Figure 3: The detection results are PV: 0.04080μm; RMS: 0.00478μm

Figure 4: The detection results are PV：0.02024μm；RMS：0.00274μm

Figure 5: The detection results are PV：0.05583μm；RMS：0.00778μm

Grating Sample No. 1: The three-dimensional and contour maps of wavefront aberration in the left, middle, and right areas of the -1 level beam are shown below:

Figure 6: The detection results are PV：0.11904μm；RMS：0.02107μm

Figure 7: The detection results are PV：0.08688μm；RMS：0.01514μm

Figure 8: The detection results are PV：0.09755μm；RMS：0.01594μm

Grating Sample No. 1: The three-dimensional and contour maps of wavefront distortion in the left, middle, and right areas of the +1 level beam are shown below:

Figure 9: The detection results are PV：0.10405μm；RMS：0.01793μm

Figure 10: The detection results are PV：0.10010μm；RMS：0.01575μm

Figure 11: The detection results are PV：0.10432μm；RMS：0.01818μm

The core advantages of FIS4-NIR in the same scenario

✅ One-time acquisition, nanometer-level precision

The actual measured 0th-order RMS is as low as 2.74nm, and the ±1st-order RMS remains stable within the range of 7-21nm

✅ Flexible positioning, multi-level measurement

The FIS4-NIR is compact in size and can be freely moved to a 0-level or ±1-level spot without requiring any changes to the optical path

✅ No vibration isolation required, usable in conventional environments

The temperature is 23℃±3℃, the humidity is 55±5%RH, there is no vibration isolation platform, and the data is clear and stable

✅ Relative measurement, deducting systematic errors

Cavity background subtraction eliminates the interference from inherent aberrations of components such as beam expanders

This test proves that FIS4-NIR possesses the characteristics of high efficiency, high precision, flexibility, and controllable cost in the transmission wavefront detection of grating device's 0th order and ±1st order split beam spots. It transforms the complex detection problem of multiple levels and positions into a common optical path self-interference information inversion, significantly reducing the dependence on vibration isolation environment and reference mirrors.

Of course, the FIS4 series of wavefront sensors is not limited to this. This test is based on the FIS4-NIR near-infrared wavelength model (operating wavelength 1064nm). In addition to its application in near-infrared scenarios, the FIS4 series can also be used in white light wavelength (400-1100nm), long-wave infrared wavelength (8-14μm), and ultraviolet wavelength (200-400nm, with a resolution of 512×512 phase points), basically covering the full wavelength range from ultraviolet to long-wave infrared.

If you are also facing the need for multi-level wavefront testing of grating devices, beam splitters, diffractive optical elements, etc., please contact us!

Obtain more technical information or schedule a sample test!