Measurement principle

DHM instrument generates, in real-time, high resolution 3D digital images of a sample using the principle of holography. Holograms are generated by combining a coherent reference wave with the wave received from a specimen (see figure below). They are recorded by a video camera and transmitted to a computer for real-time numerical reconstruction. DHM software procedures allows computation, from a single hologram acquired in a few microseconds, of the complete wavefront emanating from an object and provides: - Intensity images providing the same contrast as with classical optical microscopy, - Phase images providing quantitative data, defined at a sub-wavelength scale, used for accurate and stable measurements. In reflection, the phase image reveals directly the surface topography with a sub-nanometric vertical resolution. In transmission, the phase image reveals the phase shift induced by a transparent specimen, which depends on its thickness and refractive index. This digital approach to holography allows the application of computer based procedures at a level unreached in video-microscopy. In particular the DHM principle features software compensation of optical aberrations, digital image focusing and numerical compensation for sample tilt and environmental disturbances, making DHM instruments robust and easy to use methods for routine inspections at the nanometer and micrometer scale.

Transmission configuration	Reflection configuration