Very efficient speckle contrast reduction realized by moving diffuser device

Abstract

Speckle noise reduction is best tested on a precise speckle contrast measurement bench, which should be able to measure 100% contrast in fully developed speckle as well as the smallest contrast (for example, less than 10%) after its reduction. On such a test bench, we have measured very efficient speckle contrast reduction by temporal averaging using a moving diffuser on a tuning fork, which vibrates at 100 Hz over 60 microm in amplitude, a distance that is three times the surface roughness correlation length of the diffuser.

Optically monitoring and controlling nanoscale topography during semiconductor etching

“…The laser power was minimized to reduce unwanted etching. At the sample plane, the laser power density was 0.64 mW cm 22 , while the projector delivered 8.9 mW cm 22 . The Monitoring nanoscale topography during etching C Edwards et al 5 power density of the laser under normal imaging conditions without attenuation was 57 mW cm 22 .…”

“…At the sample plane, the laser power density was 0.64 mW cm 22 , while the projector delivered 8.9 mW cm 22 . The Monitoring nanoscale topography during etching C Edwards et al 5 power density of the laser under normal imaging conditions without attenuation was 57 mW cm 22 . The profiles through the mask and the microlens (Figure 4c) indicate that the photochemical etching process is nonlinear, i.e., the local lens height is not simply proportional to the light irradiance delivered at that point.…”

“…This method essentially averages out the effects of speckles. 21,22 It also dithers the image, which reduces the quantization error. The Monitoring nanoscale topography during etching C Edwards et al 2 resulting epi-DPM images revealed that the spatial noise floor dropped to 10.4 nm after adding the diffuser.…”

Aperture scanning Fourier ptychographic microscopy

“…For the illumination, light from a He-Ne laser (λ=632.8nm) is first shined on a rotating ground glass diffuser. The rotating diffuser decreases the temporal coherence of the light, which reduces the speckles in the captured image [10]. The scattered light from the diffuser is then collected into a multi-mode fiber, which allows for easy switching between transmissive and reflective mode.…”

Investigations of a wedge-shaped nematic liquid crystal cell using Mach–Zehnder interferometer

“…Lasers are being extensively used as backlight sources for LC displays [16][17][18]. The lasers have very high spatial coherence, brightness and color purity.…”