Albumen as a relief recording media for spatial distributions of infrared radiation. Fabrication of interference gratings and microlenses

Surface Profile Studies of Photoinduced Gratings Made with DCG Films with Optional Papain Development

The use of surface relief structures is increasing in the field of optics. A study of photoinduced relief using dichromated gelatin films with different thickness is described in this paper. Two light sources were used: a laser (λ = 468 nm) and an ultraviolet mercury-metal halide lamp. Gratings with low spatial frequencies were contact-copied on the DCG (dichromated gelatin) films. Two development processes were used, one included washing the plates with just water and the other with a mixture of water and papain. This enzyme is used to improve the gratings’ relief which was studied with a profilometer. For the development process with just water, it was found that when gratings were recorded using visible or UV light, the height profile inversely correlated to spatial frequencies. For short exposure times, the reliefs showed a sinusoidal profile. When visible light was used, the DCG areas where the Ronchi grating had transparent slits showed a flat relief and the areas where the Ronchi grating had opaque slits showed a round peak, with the peak being taller than the flat surface. In contrast, when UV light was used, the flat surfaces were taller than the peaks. The relief height increased up to seven times when papain was used.

Liquid refractive index measured through a refractometer based on diffraction gratings

We developed two versions of refractometers to measure the refractive index of liquids. One refractometer comprises a glass cell with a surface relief grating on the inner face of one of its walls, while the other one is a microfluidic channel in the form of serpentine that behaves as a grating. Measurements of the liquid refractive index were performed by sensing the first order intensity. Several liquids have been used including an organic one. Calibration plots are shown.

Digital holographic interferometry with CO2 lasers and diffuse illumination applied to large space reflector metrology [Invited]

Digital holographic interferometry in the long-wave infrared domain has been developed by combining a CO(2) laser and a microbolometer array. The long wavelength allows large deformation measurements, which are of interest in the case of large space reflectors undergoing thermal changes when in orbit. We review holography at such wavelengths and present some specific aspects related to this spectral range on our measurements. For the design of our digital holographic interferometer, we studied the possibility of illuminating specular objects by a reflective diffuser. We discuss the development of the interferometer and the results obtained on a representative space reflector, first in the laboratory and then during vacuum cryogenic test.

Electronic speckle pattern interferometry and digital holographic interferometry with microbolometer arrays at 10.6 μm

Electronic speckle pattern interferometry and digital holographic interferometry are investigated at long infrared wavelengths. Using such wavelengths allows one to extend the measurement range and decrease the sensitivity of the techniques to external perturbations. We discuss the behavior of reflection by the object surfaces due to the long wavelength. We have developed different experimental configurations associating a CO(2) laser emitting at 10.6 μm and microbolometer arrays. Phase-shifting in-plane and out-of-plane electronic speckle pattern interferometry and lensless digital holographic interferometry are demonstrated on rotation measurements of a solid object.