Digital holographic microscopy (DHM) is a quantitative phase imaging technique, where both the amplitude and phase of light interacting with a sample are measured. The phase contains information on the height and refractive index variations on a sample. In the off-axis configuration, the hologram is created between light from a sample and a reference wavefront hitting a sensor at an angle, allowing the separation of the direct reflections and the interference pattern in the frequency domain. This permits the observation of fast dynamics for a full 2D area, as the phase of the reflected/transmitted light can be retrieved numerically from a single hologram. Thus, the update rate in the surface topography and refractive index profile of a sample is limited only by the frame rate of the camera used to record the holograms.
- Lyncée Tec DHM R2104 with sample stage heating control + self-built interference lithography addition (488 nm). Measurement of sample surface topology with 1 nm z-resolution through light interference imaging.
The digital holographic microscope in Tampere University is integrated with an interference lithography system. The incident angles, polarizations, and the relative phase difference of the two laser beams used for creating the interference patterns can be chosen independently. The dynamics of the grating formation can be recorded with the full 2D field of view with a time step of 5 ms between measurements. The sample position can be scanned using computer control, allowing for patterning selected areas with grating structures.
More information on the lithography system: Rekola, H., Berdin, A., Fedele, C. et al. Digital holographic microscopy for real-time observation of surface-relief grating formation on azobenzene-containing films. Sci Rep 10, 19642 (2020). https://doi.org/10.1038/s41598-020-76573-6
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