Mr. Ianjit S. Bhatti Profile

Ianjit S. Bhatti

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Publications (7)

Proceedings Article | 20 November 2017 Open Access

Applications of immersed diffraction gratings in Earth observation from space

D. Lobb, I. Bhatti

Proceedings Volume 10565, 105651M (2017) https://doi.org/10.1117/12.2309222

KEYWORDS: Diffraction gratings, Spectrometers, Spectral resolution, Short wave infrared radiation, Silica, Near infrared, Diffraction, Optical design, Sensors, Collimators

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Proceedings Article | 20 November 2017 Open Access

Efficiency, dispersion and straylight performance tests of immersed gratings for high resolution spectroscopy in the near infrared

J. Fernandez-Saldivar, F. Culfaz, N. Angli, I. Bhatti, D. Lobb, G. Baister, B. Touzet, F. Desserouer, B. Guldimann

Proceedings Volume 10564, 105642S (2017) https://doi.org/10.1117/12.2309090

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Proceedings Article | 20 November 2017 Open Access

State of the art in silicon immersed gratings for space

Aaldert van Amerongen, Hélène Krol, Catherine Grèzes-Besset, Tonny Coppens, Ianjit Bhatti, Dan Lobb, Bram Hardenbol, Ruud Hoogeveen

Proceedings Volume 10564, 105642R (2017) https://doi.org/10.1117/12.2309092

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We present the status of our immersed diffraction grating technology, as developed at SRON and of their multilayer optical coatings as developed at CILAS. Immersion means that diffraction takes place inside the medium, in our case silicon. The high refractive index of the silicon medium boosts the resolution and the dispersion. Ultimate control over the groove geometry yields high efficiency and polarization control. Together, these aspects lead to a huge reduction in spectrometer volume. This has opened new avenues for the design of spectrometers operating in the short-wave-infrared wavelength band. Immersed grating technology for space application was initially developed by SRON and TNO for the short-wave-infrared channel of TROPOMI, built under the responsibility of SSTL. This space spectrometer will be launched on ESA's Sentinel 5 Precursor mission in 2015 to monitor pollution and climate gases in the Earth atmosphere. The TROPOMI immersed grating flight model has technology readiness level 8. In this program CILAS has qualified and implemented two optical coatings: first, an anti-reflection coating on the entrance and exit facet of the immersed grating prism, which reaches a very low value of reflectivity for a wide angular range of incidence of the transmitted light; second, a metal-dielectric absorbing coating for the passive facet of the prism to eliminate stray light inside the silicon prism. Dual Ion Beam Sputtering technology with in-situ visible and infrared optical monitoring guarantees the production of coatings which are nearly insensitive to temperature and atmospheric conditions. Spectral measurements taken at extreme temperature and humidity conditions show the reliability of these multi-dielectric and metal-dielectric functions for space environment. As part of our continuous improvement program we are presently developing new grating technology for future missions, hereby expanding the spectral range, the blaze angles and grating size, while optimizing performance parameters like stray light and wavefront error. The program aims to reach a technology readiness level of 5 for the newly developed technologies by the end of 2012. An outlook will be presented.

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Proceedings Article | 20 November 2017 Open Access

TROPOMI, the Sentinel 5 precursor instrument for air quality and climate observations: status of the current design

Robert Voors, Johan de Vries, Ianjit Bhatti, Dan Lobb, Trevor Wood, Nick van der Valk, Ilse Aben, Pepijn Veefkind

Proceedings Volume 10564, 105641Q (2017) https://doi.org/10.1117/12.2309017

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TROPOMI, the Tropospheric Monitoring Instrument, is a passive UV-VIS-NIR-SWIR trace gas spectrograph in the line of SCIAMACHY (2002) and OMI (2004), instruments with the Netherlands in a leading role. Both instruments are very successful and remained operational long after their nominal life time.

TROPOMI is the next step, scheduled for launch in 2015. It combines the broad wavelength range from SCIAMACHY from UV to SWIR and the broad viewing angle push-broom concept from OMI, which makes daily global coverage in combination with good spatial resolution possible. Using spectral bands from 270-500nm (UV-VIS) 675-775nm (NIR) and 2305-2385nm (SWIR) at moderate resolution (0.25 to 0.6nm) TROPOMI will measure O3, NO2, SO2, BrO, HCHO and H2O tropospheric columns from the UV-VIS-NIR wavelength range and CO and CH4 tropospheric columns from the SWIR wavelength range. Cloud information will be derived primarily from the O2A band in the NIR. This will help, together with the aerosol information, in constraining the light path of backscattered solar radiation. Methane (CH4), CO2 and Carbon monoxide (CO) are the key gases of the global carbon cycle. Of these, Methane is by far the least understood in terms of its sources and is most difficult to predict its future trend. Global space observations are needed to inform atmospheric models. The SWIR channel of TROPOMI is designed to achieve the spectral, spatial and SNR resolution required for this task.

TROPOMI will yield an improved accuracy of the tropospheric products compared to the instruments currently in orbit. TROPOMI will take a major step forward in spatial resolution and sensitivity. The nominal observations are at 7 x 7 km2 at nadir and the signal-to-noises are sufficient for trace gas retrieval even at very low albedos (down to 2%). This spatial resolution allows observation of air quality at sub-city level and the high signal-to-noises means that the instrument can perform useful measurements in the darkest conditions.

TROPOMI is currently in its detailed design phase. This paper gives an overview of the challenges and current performances. From unit level engineering models first results are becoming available. Early results are promising and this paper discusses some of these early H/W results.

TROPOMI is the single payload on the Sentinel-5 precursor mission which is a joint initiative of the European Community (EC) and of the European Space Agency (ESA). The 2015 launch intends to bridge the data stream from OMI / SCIAMACHY and the upcoming Sentinel 5 mission. The instrument is funded jointly by the Netherlands Space Office and by ESA. Dutch Space is the instrument prime contractor. SSTL in the UK is developing the SWIR module with a significant contribution from SRON. Dutch Space and TNO are working as an integrated team for the UVN module. KNMI and SRON are responsible for ensuring the scientific capabilities of the instrument.

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Proceedings Article | 18 July 2014 Paper

Cryogenic optical mounting for short-wave infrared spectrometers

J. Grant, T. Wood, I. Bhatti, A. Cañas, P. Reddick, P. van Wyk, S. Bharadia, T. Storey, T. Potterton, W. Rits, H. Meijer

Proceedings Volume 9151, 91513Z (2014) https://doi.org/10.1117/12.2057986

KEYWORDS: Adhesives, Prisms, Sensors, Short wave infrared radiation, Silicon, Spectrometers, Optical mounts, Germanium, Cryogenics, Titanium

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In order to measure atmospheric concentrations of carbon monoxide, methane, water and carbon dioxide from spaceborne platforms, Short-Wave Infrared (SWIR) immersed grating spectrometers are employed. Due to the need to minimise detector dark current and internal black body radiation from the spectrometer’s own structure, these instruments are operated at cryogenic temperatures. ESA’s Sentinel 5-Precursor is a small satellite science mission; the platform comprises the Tropospheric Monitoring Instrument (TROPOMI), which includes a SWIR module. Optical mounts have been developed for the SWIR module which meet the requirements to cope with the differences in thermal expansion between the optical elements and their structural mounts over cryogenic temperature ranges, be robust against the mechanical environment during launch, and maintain optical alignment stability with a tight volume constraint. Throughout the design of the SWIR spectrometer, flexures were deployed to control deformations due to thermal expansion, the design of interfaces between materials of differing coefficient of thermal expansion was carefully managed, and the geometry of adhesive pads was tightly controlled. Optical mounting concepts were evaluated using finite element analysis (FEA). A breadboard programme was undertaken to verify these concepts. FEA and breadboard results were correlated to provide confidence in the design. The breadboard programme consisted of thermal cycling and pull-testing of adhesive joints, as well as environmental and optical testing of representative subsystems. Analysis and breadboarding demonstrated that the optical mounting design will survive the mechanical and thermal environments, and verified the stability of the optical alignment requirements. Novel optical mounting structures have been designed, analysed, assembled, tested and integrated into the optical assemblies of the TROPOMI SWIR spectrometer, creating a compact and robust state of the art instrument. These concepts are applicable to instruments for astronomical missions aiming to characterise exoplanets, as well as Earth observation missions.

Proceedings Article | 16 October 2013 Paper

The TROPOMI instrument: first H/W results

Robert Voors, Johan de Vries, Nick van der Valk, Ianjit Bhatti, David Woods, Ilse Aben, Ruud Hoogeveen, Pepijn Veefkind, Quintus Kleipool

Proceedings Volume 8889, 88890Q (2013) https://doi.org/10.1117/12.2028848

KEYWORDS: Short wave infrared radiation, Sensors, Electronics, Telescopes, Optical benches, Spectroscopy, Space telescopes, Space operations, Calibration, Spectrographs

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Proceedings Article | 22 September 2011 Paper

Straylight measurements of immersed gratings for high-resolution spectroscopy in the near infrared

J. Fernandez-Saldivar, I. Bhatti, D. Lobb, B. Touzet, B. Guldimann

Proceedings Volume 8167, 816719 (2011) https://doi.org/10.1117/12.899889

KEYWORDS: Stray light, Diffraction gratings, Diffraction, Spectrometers, Prisms, Optical design, Spectral resolution, Light scattering, Zemax, Mirrors

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