NOMAD spectrometer on the ExoMars trace gas orbiter mission: part 2—design, manufacturing, and testing of the ultraviolet and visible channel

NOMAD is a spectrometer suite on board the ESA/Roscosmos ExoMars Trace Gas Orbiter, which launched in March 2016. NOMAD consists of two infrared channels and one ultraviolet and visible channel, allowing the instrument to perform observations quasi-constantly, by taking nadir measurements at the day- and night-side, and during solar occultations. Here, in part 2 of a linked study, we describe the design, manufacturing, and testing of the ultraviolet and visible spectrometer channel called UVIS. We focus upon the optical design and working principle where two telescopes are coupled to a single grating spectrometer using a selector mechanism

A method for polarisation imaging using digital holography

A numerical holographic method, which is able to determine the amplitude components of the Jones vector of a wavefront in addition to its phase and amplitude, is presented. Two reference waves, with orthogonal polarisations interfere with the transmitted or reflected object wave to create the hologram that is recorded on a standard CCD camera. Two wavefronts, one for each perpendicular polarisation state, are numerically reconstructed in intensity. Combining the intensity distribution of these two wavefronts permits to determine the amplitude component of the Jones vector of the object wavefront. We show that this method can be used to image the distribution of a part of the polarisation state at the surface of the specimen. Preliminary results obtained with a polariser as specimen indicates that the method can be used to obtain quantitative data about the polarisation state

Polarization imaging by use of digital holography.

We present what we believe to be a new digital holographic imaging method that is able to determine simultaneously the distributions of intensity, phase, and polarization state at the surface of a specimen on the basis of a single image acquisition. Two reference waves with orthogonal polarization states interfere with the object wave to create a hologram that is recorded on a CCD camera. Two wave fronts, one for each perpendicular polarization state, are numerically reconstructed in intensity and phase. Combining the intensity and the phase distributions of these two wave fronts permits the determination of all the components of the Jones vector of the object-wave front. We show that this method can be used to image and measure the distribution of the polarization state at the surface of a specimen, and the obtained results indicate that precise quantitative measurements of the polarization state can be achieved. An application of the method to image the birefringence of a stressed polymethyl methacrylate sample is presented

Compact laser scanning confocal microscope

Within the framework of the General Support Technology Program of the European Space Agency (ESA), a compact dedicated confocal laser scanning microscope has been developed for 3D fluorescence imaging of biological samples. The microscope permits normal confocal mode operation with excitation at 488nm and fluorescence lifetime imaging (FLIM) with excitation at 630nm and a time resolution of 200ps. Each fluorescence signal is detected by a dedicated photomultiplier tube. Proper optical signal separation and filtering is performed by a set of optical filters and dichroics. The software and hardware further include the specific imaging modes allowing for fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP). In addition to this dual wavelength fluorescence imaging mode, the microscope includes transmission imaging capabilities via differential imaging contrast (DIC). Both fluorescence and DIC imaging can be acquired simultaneously. The source for the DIC is a near infrared LED. This choice permits the decoupling of DIC and fluorescence signals by a dichroic cold mirror. The opto-mechanical assembly is constructed on the two sides of a rigid 16mm thick aluminum base plate of dimensions 389 mm by 575.5 mm. The total volume under light and dust shielding removable covers is just 53 dm3, excluding PC and control electronics. In this paper, the design, performance and limitations of this compact confocal microscope are discussed. Illustrative examples of applications on biological samples are show

Interferometric precision with Fourier-based deflectometry

Optical components are routinely tested with inteferometric based techniques. It is show in this paper that Fourier based deflectometry method can be used for optical component inspection through very sensitive and precise wavefront reconstruction. The wavefront is expressed from the raw measurements of the wavefront derivatives as a Zernike polynomial expansion. The form of the polynomials permits absolute instrumental error characterization by repeated measurement of the element under test oriented at several azimuthal angles. It is shown that nanometric precision of Zernike based reconstructions can be performed and that the air turbulences are the experimental limiting factor to the instrumental precision.Anglai

Single acquisition polarisation imaging with digital holography

A demonstration of the ability of digital holography to image and to measure spatial variations of the polarisation of an object wave with a single image acquisition is presented. This is achieved by recording a hologram with two reference beams presenting orthogonal polarisations and different propagation directions. A CCD camera is used to record the hologram and the reconstruction is performed numerically