Ground-based and Airborne Instrumentation for Astronomy VII, Jul 10, 2018
MOSAIC is a concept for a multi-object spectrograph for the Extremely Large Telescope (ELT). It i... more MOSAIC is a concept for a multi-object spectrograph for the Extremely Large Telescope (ELT). It is planned to cover the wavelength range from 460 nm to 1800 nm with two types of spectrographs, optimized for the visible and the near-infrared. There are two observing modes; multiplex mode with 200 sampling points and Integral Field Unit (IFU) mode with 10 fields. The instrument consists of 5 visible spectrographs and 5 near-infrared spectrographs. The ELT is far from diffraction limited in the visible wavelength range. Rather than developing a large and complex AO system, it was decided that the instrument will be seeing limited in the visible. Spot sizes are therefore about 2.8 mm in diameter in the ELT focal plane, and need to be sampled by multiple fibers with large core diameter. As a result, large optics is required to achieve the science requirements on spectral resolution, bandwidth and multiplex. We work in close collaboration with manufacturers to design an instrument that is feasible and meets the scientific requirements.
A spherical concave diffraction grating was chosen as the dispersing element for a number of spec... more A spherical concave diffraction grating was chosen as the dispersing element for a number of spectroscopic devices. More recent application of these grating is designing of multiplexers/demultiplexers for wavelength routed optical networks. Concave grating acts as the focusing element and can be the sole optical element of a device, which simplifies its adjustment and increases the transmittance. However, it possesses aberrations. Conventional method of concave diffraction grating recording using interference of two spherical waves formed using dividing and expanding of laser beam, gives possibility to minimize three main types of aberrations, the defocusing, the meridional coma and the first order astigmatism. For the wide range of spectrometers these gratings can be used with rather good results. However, if we want to design spectrometer with increased aperture, wide spectral region or extremely high resolving power, we have to take into consideration per limit more two aberrations-the sagital coma and the spherical aberration. We also have this problem in designing of wavelength routers, where aberration geometric size of image should be not more than the optical fiber diameter. We can resolve this problem using aspheric wavefront recording systems. Since refraction optics is not good for holographic recording because of scattering, this systems can include mirrors or other diffraction gratings. In present work different recording systems are discussed from the point of view of geometric theory of grating (including multisteps recording process) and from the point of view of reality of experimental installing and using of these systems as well.
Multimodal spectral histopathology (MSH), an optical technique combining tissue auto-fluorescence... more Multimodal spectral histopathology (MSH), an optical technique combining tissue auto-fluorescence (AF) imaging and Raman micro-spectroscopy (RMS), was previously proposed for detection of residual basal cell carcinoma (BCC) at the surface of surgically-resected skin tissue. Here we report the development of a fully-automated prototype instrument based on MSH designed to be used in the clinic and operated by a non-specialist spectroscopy user. The algorithms for the AF image processing and Raman spectroscopy classification had been first optimised on a manually-operated laboratory instrument and then validated on the automated prototype using skin samples from independent patients. We present results on a range of skin samples excised during Mohs micrographic surgery, and demonstrate consistent diagnosis obtained in repeat test measurement, in agreement with the reference histopathology diagnosis. We also show that the prototype instrument can be operated by clinical users (a skin su...
This paper shows how holographic diffraction gratings fabricated on spherical substrates by means... more This paper shows how holographic diffraction gratings fabricated on spherical substrates by means of wavefront interference can be used to create aspheric wavefronts and thereby to fabricate concave diffraction gratings that have virtually no aberration limitations in high-resolution spectral devices.
TGS begins to be rapidly and irreversibly colored on heating under vacuum at about 170~ and TGSe ... more TGS begins to be rapidly and irreversibly colored on heating under vacuum at about 170~ and TGSe does the same above 150~ The crystals become coated with the decomposition products, which are largely responsible for the absorption spectra and prevent decomposition products escaping from underlying layers, so they thus restrict the further damage. The general increase in absorption at 250-1000 nm indicates that the temperature has been reached where damage is rapid. Below the rapid-cooling threshold, TGS and TGSe show weak absorption anomalies corresponding to the temperatures for the phasetransitions Tc, the unipolar state annealing, birefringence change, and evaporation.
The geometrical theory of gratings is extended to the case of recording by means of a backreflect... more The geometrical theory of gratings is extended to the case of recording by means of a backreflected beam. An analysis is given of the possibilities of developing this recording method further and of extending the region in which the resulting gratings are used in spectral devices.
The latest advances in the field of holographic gratings and spectral devices is in calculation, ... more The latest advances in the field of holographic gratings and spectral devices is in calculation, manufacture and use of these gratings for spectral devices. The general theory of diffraction grating was developed in 1974 1. Although this theory is in wide use, not all the problems associated with the theory have been resolved. Theoretical calculations show that this is possible using a more complicated mounting of recording the grating 2 .
The layout has entrance and exit slits and concave diffraction grating, made rotating. The gratin... more The layout has entrance and exit slits and concave diffraction grating, made rotating. The grating has a varying distance of between lines, satisfying relationship d = do (1+ mu.y + nu.y sq) where do is the line separation at the grating apex: 4-coordinate perpendicular to lines : mu, nu coefficients of inequality in spacing. Entrance (1) and exit (2) slits are connected by diffraction rays at concave grating (3) with rocking control (4). Distances r' to exit slit and r to entrance slit from grating (3) are defined as 1.15...1.55 in the plus first diffraction order. To increase light power and extend working range the line spacing inequality is prescribed by the relation nu = mu sq.-3/2 times r' over (5...6) r.R sq: where R is the radius of curvature of concave grating (3). USE/ADVANTAGE-An optical spectral instrument is designed for increased light power and a widened working range without exchanging gratings. Bul. 43/23.11.90
Ground-based and Airborne Instrumentation for Astronomy VII, Jul 10, 2018
MOSAIC is a concept for a multi-object spectrograph for the Extremely Large Telescope (ELT). It i... more MOSAIC is a concept for a multi-object spectrograph for the Extremely Large Telescope (ELT). It is planned to cover the wavelength range from 460 nm to 1800 nm with two types of spectrographs, optimized for the visible and the near-infrared. There are two observing modes; multiplex mode with 200 sampling points and Integral Field Unit (IFU) mode with 10 fields. The instrument consists of 5 visible spectrographs and 5 near-infrared spectrographs. The ELT is far from diffraction limited in the visible wavelength range. Rather than developing a large and complex AO system, it was decided that the instrument will be seeing limited in the visible. Spot sizes are therefore about 2.8 mm in diameter in the ELT focal plane, and need to be sampled by multiple fibers with large core diameter. As a result, large optics is required to achieve the science requirements on spectral resolution, bandwidth and multiplex. We work in close collaboration with manufacturers to design an instrument that is feasible and meets the scientific requirements.
A spherical concave diffraction grating was chosen as the dispersing element for a number of spec... more A spherical concave diffraction grating was chosen as the dispersing element for a number of spectroscopic devices. More recent application of these grating is designing of multiplexers/demultiplexers for wavelength routed optical networks. Concave grating acts as the focusing element and can be the sole optical element of a device, which simplifies its adjustment and increases the transmittance. However, it possesses aberrations. Conventional method of concave diffraction grating recording using interference of two spherical waves formed using dividing and expanding of laser beam, gives possibility to minimize three main types of aberrations, the defocusing, the meridional coma and the first order astigmatism. For the wide range of spectrometers these gratings can be used with rather good results. However, if we want to design spectrometer with increased aperture, wide spectral region or extremely high resolving power, we have to take into consideration per limit more two aberrations-the sagital coma and the spherical aberration. We also have this problem in designing of wavelength routers, where aberration geometric size of image should be not more than the optical fiber diameter. We can resolve this problem using aspheric wavefront recording systems. Since refraction optics is not good for holographic recording because of scattering, this systems can include mirrors or other diffraction gratings. In present work different recording systems are discussed from the point of view of geometric theory of grating (including multisteps recording process) and from the point of view of reality of experimental installing and using of these systems as well.
Multimodal spectral histopathology (MSH), an optical technique combining tissue auto-fluorescence... more Multimodal spectral histopathology (MSH), an optical technique combining tissue auto-fluorescence (AF) imaging and Raman micro-spectroscopy (RMS), was previously proposed for detection of residual basal cell carcinoma (BCC) at the surface of surgically-resected skin tissue. Here we report the development of a fully-automated prototype instrument based on MSH designed to be used in the clinic and operated by a non-specialist spectroscopy user. The algorithms for the AF image processing and Raman spectroscopy classification had been first optimised on a manually-operated laboratory instrument and then validated on the automated prototype using skin samples from independent patients. We present results on a range of skin samples excised during Mohs micrographic surgery, and demonstrate consistent diagnosis obtained in repeat test measurement, in agreement with the reference histopathology diagnosis. We also show that the prototype instrument can be operated by clinical users (a skin su...
This paper shows how holographic diffraction gratings fabricated on spherical substrates by means... more This paper shows how holographic diffraction gratings fabricated on spherical substrates by means of wavefront interference can be used to create aspheric wavefronts and thereby to fabricate concave diffraction gratings that have virtually no aberration limitations in high-resolution spectral devices.
TGS begins to be rapidly and irreversibly colored on heating under vacuum at about 170~ and TGSe ... more TGS begins to be rapidly and irreversibly colored on heating under vacuum at about 170~ and TGSe does the same above 150~ The crystals become coated with the decomposition products, which are largely responsible for the absorption spectra and prevent decomposition products escaping from underlying layers, so they thus restrict the further damage. The general increase in absorption at 250-1000 nm indicates that the temperature has been reached where damage is rapid. Below the rapid-cooling threshold, TGS and TGSe show weak absorption anomalies corresponding to the temperatures for the phasetransitions Tc, the unipolar state annealing, birefringence change, and evaporation.
The geometrical theory of gratings is extended to the case of recording by means of a backreflect... more The geometrical theory of gratings is extended to the case of recording by means of a backreflected beam. An analysis is given of the possibilities of developing this recording method further and of extending the region in which the resulting gratings are used in spectral devices.
The latest advances in the field of holographic gratings and spectral devices is in calculation, ... more The latest advances in the field of holographic gratings and spectral devices is in calculation, manufacture and use of these gratings for spectral devices. The general theory of diffraction grating was developed in 1974 1. Although this theory is in wide use, not all the problems associated with the theory have been resolved. Theoretical calculations show that this is possible using a more complicated mounting of recording the grating 2 .
The layout has entrance and exit slits and concave diffraction grating, made rotating. The gratin... more The layout has entrance and exit slits and concave diffraction grating, made rotating. The grating has a varying distance of between lines, satisfying relationship d = do (1+ mu.y + nu.y sq) where do is the line separation at the grating apex: 4-coordinate perpendicular to lines : mu, nu coefficients of inequality in spacing. Entrance (1) and exit (2) slits are connected by diffraction rays at concave grating (3) with rocking control (4). Distances r' to exit slit and r to entrance slit from grating (3) are defined as 1.15...1.55 in the plus first diffraction order. To increase light power and extend working range the line spacing inequality is prescribed by the relation nu = mu sq.-3/2 times r' over (5...6) r.R sq: where R is the radius of curvature of concave grating (3). USE/ADVANTAGE-An optical spectral instrument is designed for increased light power and a widened working range without exchanging gratings. Bul. 43/23.11.90
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Papers by Elena Sokolova