Gary Hawkins

University of Oxford | OX · Department of Physics

With a growing interest in mid- and far-infrared astronomy using cooled imaging and spectrometer instruments in highaltitude observatories and spaceflight telescopes, it is becoming increasingly important to characterise and assess the spectral performance of cooled multilayer filters across the Q-band atmospheric window. This region contains spect...

Currently, infrared filters for astronomical telescopes and satellite radiometers are based on multilayer thin film stacks of alternating high and low refractive index materials. However, the choice of suitable layer materials is limited and this places limitations on the filter performance that can be achieved. With the introduction of metamateria...

This paper reports the first derived thermo-optical properties for vacuum deposited infrared thin films embedded in multilayers. These properties were extracted from the temperature-dependence of manufactured narrow bandpass filters across the 4-17 µm mid-infrared wavelength region. Using a repository of spaceflight multi-cavity bandpass filters, t...

The ability of narrow bandpass filters to discriminate wavelengths between closely-separated gas absorption lines is crucial in many areas of infrared spectroscopy. As improvements to the sensitivity of infrared detectors enables operation in uncontrolled high-temperature environments, this imposes demands on the explicit bandpass design to provide...

The Earth Cloud, Aerosol and Radiation Explorer mission (EarthCARE) Multispectral Imager (MSI) is a radiometric instrument designed to provide the imaging of the atmospheric cloud cover and the cloud top surface temperature from a sun-synchronous low Earth orbit. The MSI forms part of a suite of four instruments destined to support the European Spa...

NDIR is proposed for monitoring of air pollutants emitted by ship engines. Careful optical filtering overcomes the challenge of optical detection of NO2 in humid exhaust gas, despite spectroscopic overlap with the water vapour band.

The sea and land surface temperature radiometer (SLSTR) is a nine-channel visible and infrared high-precision radiometer designed to provide climate data of global sea and land surface temperatures. The SLSTR payload is destined to fly on the Ocean and Medium-Resolution Land Mission for the ESA/EU global monitoring for environment and security (GME...

As improvements to the optical design of spectrometer and radiometer instruments evolve with advances in detector sensitivity, use of focal plane detector arrays and innovations in adaptive optics for large high altitude telescopes, interest in mid-infrared astronomy and remote sensing applications have been areas of progressive research in recent...

As improvements to the optical design of spectrometer and radiometer instruments evolve with advances in detector sensitivity, use of focal plane detector arrays and innovations in adaptive optics for large high altitude telescopes, interest in mid-infrared astronomy and remote sensing applications have been areas of progressive research in recent...

Modal filtering is based on the capability of single-mode waveguides to transmit only one complex amplitude function to eliminate virtually any perturbation of the interfering wavefronts, thus making very high rejection ratios possible in a nulling interferometer. In the present paper we focus on the progress of Integrated Optics in the thermal inf...

Increasing legislation has steadily been introduced throughout the world to restrict the use of heavy metals, particularly cadmium (Cd) and lead (Pb) in high temperature pigments, ceramics, and optoelectronic material applications. Removal of cadmium from thin-film optical and semiconductor device applications has been hampered by the absence of vi...

The cooled infrared filters and dichroic beam splitters manufactured for the Mid-Infrared Instrument are key optical components for the selection and isolation of wavelengths in the study of astrophysical properties of stars, galaxies, and other planetary objects. We describe the spectral design and manufacture of the precision cooled filter coatin...

This paper describes the design and manufacture of a set of precision cooled (210K) narrow-bandpass filters for the infrared imager and sounder on the Indian Space Research Organisation (ISRO) INSAT-3D meteorological satellite. We discuss the basis for the choice of multilayer coating designs and materials for 21 differing filter channels, together...

New Sn-based materials have been deposited and characterised in terms of their optical and mechanical properties and compared with existing cadmium-based thin films that currently find wide spread use in the optoelectronic and semiconductor industries.

The spectral design and fabrication of cooled (7K) mid-infrared dichroic beamsplitters and bandpass filter coatings for the MIRI spectrometer and imager are described. Design methods to achieve the spectral performance and coating materials are discussed.

The spectral design and manufacture of precision mid-infrared bandpass filters for the JPL Diviner experiment focal plane array is described. Design methods to achieve the spectral requirements, selection of materials and physical construction are discussed.

The health risks associated with the inhalation or ingestion of cadmium are well documented. During the past 18 years, EU legislation has steadily been introduced to restrict its use, leaving a requirement for the development of replacement materials. This paper looks at possible alternatives to various cadmium II-VI dielectric compounds used in th...

In this paper we report the observation of drifts in the responsivity of cryogenically cooled InSb detector-based infrared filter radiometers which have very strong wavelength dependence. These drifts can result in the increase or decrease of the response of the filter radiometers by over 5%. The origin of these variations was investigated and was...

The spectrometer sub-system of the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) contains four channels which spectrally multiplex the incoming radiation. This incident radiation, spanning a wavelength range from 4.8 to 28.8mum is spectrally divided between the channels using sets of three dichroics combined in series along the o...

This paper presents the experimental results on the low temperature absorption and dispersion properties for a variety of frequently used infrared filter substrate materials. Index of refraction (n) and transmission spectra are presented for a range of temperatures 300–50 K for the Group IV materials silicon (Si) and germanium (Ge), and Group II–VI...

The VISIR instrument for the European Southern Observatory (ESO) Very Large Telescope (VLT) is a thermal-infrared imager and spectrometer currently being developed by the French Service d'Astrophysique of CEA Saclay, and Dutch NFRA ASTRON Dwingeloo consortium. This cryogenic instrument will employ precision infrared bandpass filters in the N-(λ=7.5...

The VISIR instrument for the European Southern Observatory (ESO) Very Large Telescope (VLT) is a thermal-infrared imager and spectrometer currently being developed by the French Service d'Astrophysique of CEA Saclay, and Dutch NFRA ASTRON Dwingeloo consortium. This cryogenic instrument will employ precision infrared bandpass filters in the N-(lambd...

We describe the spectral design and manufacture of the narrow-bandpass filters and 6-18-microm broadband antireflection coatings for the 21-channel High Resolution Dynamics Limb Sounder. A method of combining the measured spectral characteristics of each filter and antireflection coating, together with the spectral response of the other optical ele...

We describe the spectral design and manufacture of the narrow-bandpass filters and 6–18-μm broadband antireflection coatings for the 21-channel High Resolution Dynamics Limb Sounder. A method of combining the measured spectral characteristics of each filter and antireflection coating, together with the spectral response of the other optical element...

A spectral performance model, designed to simulate the system spectral throughput for each of the 21 channels in the High Resolution Dynamics Limb Sounder (HIRDLS) radiometer, is described. This model uses the measured spectral characteristics of each of the components in the optical train, appropriately corrected for their optical environment, to...

The HIRDLS instrument contains 21 spectral channels spanning a wavelength range from 6 to 18 micrometer. For each of these channels the spectral bandwidth and position are isolated by an interference bandpass filter at 301 K placed at an intermediate focal plane of the instrument. A second filter cooled to 65 K positioned at the same wavelength but...

This paper describes the design and manufacture of the filters and antireflection coatings used in the HIRDLS instrument. The multilayer design of the filters and coatings, choice of layer materials, and the deposition techniques adopted to ensure adequate layer thickness control is discussed. The spectral assessment of the filters and coatings is...

This paper reports on the design and manufacture of an ultra-wide (5–30 μm) infrared edge filter for use in FTIR studies of the low frequency vibrational modes of metallo-proteins. We present details of the spectral design and manufacture of such a filter which meets the demanding bandwidth and transparency requirements of the application, and spec...

The design and manufacture of the band-defining filters and their associated dichroic beam splitter for the 11- and the 12-mu m infrared channels of the advanced along-track scanning radiometer are described. The filter requirements that have led to the choice of coating designs, coating materials, disposition of coatings, and effects of polarizati...

This paper describes the optical layout and spectral design requirements for filtering in the High-Resolution Dynamics Limb Sounder and reports progress o the manufacturing and testing of the submillimeter-sized cooled filters. We also report on the spectral and environmental performance of prototype wideband antireflection coatings that cover the...

Cooled infrared filters have been used in pressure modulation and filter radiometry to measure the dynamics, temperature distribution and concentrations of atmospheric elements in various satellite radiometers. Invariably such instruments use precision infrared bandpass filters and coatings for spectral selection, often operating at cryogenic tempe...

The High Resolution Dynamics Limb Sounder is described, with particular reference to the atmospheric measurements to be made and the rationale behind the measurement strategy. The demands this strategy places on the filters to be used in the instrument and the designs to which this leads to are detailed. A second set of filters at an intermediate i...

© 1992 Optical Society of America

Infrared optical multilayer filters and materials were exposed to the space environment of low Earth orbit on LDEF. The effects are summarized of that environment on the physical and optical properties of the filters and materials flown.

A method of designing multi-cavity narrowband filters is presented, which is based on a Tschebyshev optical prototype bandpass filter, the equivalent index concept and the variation of phases through the filter structure. Some design results are given.

The University of Reading experiment exposed IR interference filters and crystal substrates on identical earth facing and leading-edge sites of the Long Duration Exposure Facility (LDEF). Filters mostly comprised multilayer coatings of lead telluride (PbTe)/II-IV on germanium (Ge) and other substrates: crystals comprised CdTe, MgF2, sapphire, quart...

The paper addresses an experiment carried out at the Long Duration Exposure Facility (LDEF) launched by the Space Shuttle. High-performance infrared filters, coatings, and materials were exposed to the complete diversity of space radiations and temperature excursions. Transmission measurements obtained and processed from an infrared spectrophotomet...

System aspects of filter radiometer optics used to sense planetary atmospheres are described. Thus the lenses and filters in longwave channels of the Mars Observer PMIRR Pressure Modulator Infra Red Radiometer instrument are assessed individually, and as systems at 20.7 μm, 31.9 μm, 47.2 μm wavelength. A window filter and a longwave calibration fil...

The development of a set of multi-channel dichroics which includes a 6 channel dichroic operating over the wavelength region from 0.3 to 52 microns is described. In order to achieve the optimum performance, the optical constraints of PbTe, Ge, and CdTe coatings in the strongly absorptive region have been determined by use of a new iterative method...

Lead telluride is an important coating material in the infrared, and its optical and semiconductor properties are dependent on various factors contributing to its performance. The temperature dependent effects of single layer lead telluride coatings on the dispersion and absorption characteristics, absorption edge, and carrier concentration from 15...

A low-temperature model is described for infrared multilayer filters containing PbTe (or other semiconductor) and ZnSe (or other II/VI). The model is based on dielectric dispersion with semiconductor carrier dispersion added. It predicts an improved performance on cooling such as would be useful to avoid erroneous signals from the optics in spacefl...

An account is given of the coated optical elements in the two radiometric test channels of the Improved Stratospheric And Mesospheric Sounder (ISAMS), which is designed for earth atmosphere measurements in the 4.6-16.6 microns range. Comparisons are made between ISAMS spectral performance computations and measurements from actual coatings, includin...

The improvements obtained on cooling atmospheric remote-sensing instruments for space flight applications has promoted research in the characterization of optical filters necessary for spectral selection. By modeling the effects of temperature on the dispersive spectrum of some constituent thin film materials, the cooled performance can be simulate...

The design of filters for the 15-40 µm part of the spectrum is a challenge because of physical and material limitations. This paper presents the latest developments in this area, based on both multilayer and structured materials, and includes a discussion of filters fabricated for the NASA-JPL Mars Climate Sounder.