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