Remote submm-wave spectrometers have the capability of providing statistically significant numbers of isotopic composition measurements within the budget constraints of available planetary missions. This talk will present a mission and instrument concept that would enable an accurate measurement of the D/H ratio on not one but several dozens of comets in a four-year mission lifetime. The instrument would utilize advanced cryogenic detectors that would allow us to measure the abundance of the para and ortho spin states of water and its isotopologues. State of the art superconducting heterodyne receivers have been developed that provide detection sensitivities approaching the quantum limit in the 500 GHz frequency range enabling the measurement of D/H ratio on around 50 comets from an observatory stationed for example at the thermally benign Lagrange point L2
We report on the performance of a high sensitivity 4.7 THz heterodyne receiver based on a NbN hot electron bolometer mixer and a quantum cascade laser (QCL) as local oscillator. The receiver is developed to observe the astronomically important neutral atomic oxygen [OI] line at 4.7448 THz on a balloon based telescope. The single-line frequency control and improved beam pattern of QCL have taken advantage of a third-order distributed feedback structure. We measured a double sideband receiver noise temperature (Trec(DSB)) of 815 K, which is ~ 7 times the quantum noise limit (hν/2kB). An Allan time of 15 s at an effective noise fluctuation bandwidth of 18 MHz is demonstrated. Heterodyne performance was further supported by a measured methanol line spectrum around 4.7 THz.
We report a new experiment on a high-resolution heterodyne spectrometer using a 3.5 THz quantum cascade laser
(QCL) as local oscillator (LO) and a superconducting hot electron bolometer (HEB) as mixer by stabilizing both
frequency and amplitude of the QCL. The frequency locking of the QCL is demonstrated by using a methanol molecular
absorption line, a proportional-integral-derivative (PID) controller, and a direct power detector. We show that the LO
locked linewidth can be as narrow as 35 KHz. The LO power to the HEB is also stabilized by means of swing-arm
actuator placed in the beam path in combination of a second PID controller.
We report on a twin-slot antenna coupled superconducting NbN hot electron bolometer (HEB) mixer designed for 1.6
THz. Terahertz (THz) radiation is quasi-optically coupled to the HEB with an uncoated elliptical Si lens. Measured DSB
receiver noise temperatures are 1500 K at 0.85 THz, 1200 K at 1.27 THz, 1100 K at 1.31 THz, 1100 K at 1.4 THz, and
1000 K at 1.63 THz. This value at 1.63 THz is reduced to 750 K when the hot/cold loads in vacuum are used. The
frequency dependence of the noise temperature is consistent with the measured FTS spectral response. The measured farfield
beam patterns of the lens/antenna combination show nearly collimated beams with the side lobes below -16dB by
adding a 40 μm extension to a standard Si elliptical lens design, which is understood by considering a slightly lower
dielectric constant of Si (εSi) of 11.4 instead of 11.7. The good performance of such NbN HEB mixers makes it suitable
for future high-resolution spectroscopic astronomical applications.
We report on the application of a new technique for actively stabilizing the power of a far infrared gas laser as the local
oscillator (LO) in a superconducting hot electron bolometer (HEB) heterodyne receiver system at 2.5 THz. The
technique utilizes PID feedback control of the local oscillator intensity by means of a voice-coil based swing arm
actuator placed in the beam path. The HEB itself is used as a direct detector to measure incident LO power whilst
simultaneously continuing to function as heterodyne mixer. Results presented here demonstrate a factor of 50
improvement in the measured total power and spectroscopic Allan variance time. Allan times of 30 seconds and 25
seconds respectively are shown for large and small area HEB's with a measured effective noise fluctuation bandwidth of
12 MHz. The technique is versatile and can be applied to any LO source and at any LO frequency.
We have developed a novel light source for flat fielding and transmission monitoring of the Mid-Infrared Instrument on
the JWST. The source uses a hot tungsten filament, mounted in a hemispherical, non-imaging flux concentrator. The
design is compact, with the hemisphere having a diameter of 20 mm, and dissipates only 10 milliWatts of electrical
power when operating.
We describe the most important features of the design, and present the first measurements of its photometric
We present details of a new illumination source, suitable for use on mid-infrared satellite instruments. The device is
based around an electrically heated tungsten filament. The source is compact, and dissipates typically 9 mW for an
effective black-body temperature of 1000 K. A typical device design will warm from 4 K to 1000 K in around 1 s, and
cool from 1000 K to 4 K in around 2.5 s. We present results for a range of device designs, and discuss the range of
parameter space (e.g. power dissipation, time constant, photon flux) to which these devices can be tuned.
A device of this type is currently in qualification for flight on JWST-MIRI1, and similar devices are being considered
for use on JWST-NIRSPEC and SPICA2-ESI3.
We report on the progress of a far-infrared/submillimeter radiometer being developed in Cardiff for the measurement of cirrus clouds. Remote sensing of cirrus clouds is known to be of great importance to the long-term accuracy of current General Circulation Models (GCM) and climate prediction but with greater measurement coverage needed. The instrument reported here is an aircraft deployed, 5 channel fixed band radiometer capable of retrieving cirrus Ice Water Path (IWP) and mean particle diameter (Dme) using a spectral range of between 10 cm-1 and 55 cm-1. The radiometer will capitalise on ongoing measurements from the Fourier transform interferometer based, Far-infrared Sensor for Cirrus (FIRSC), an instrument for which Cardiff has been closely associated. Initial results of channel selection simulations are presented here with comparisons between different combinations of channel frequency and bandwidths, along with the number of channels used and cloud particle shape. Also demonstrated is the effect of instrument noise on retrieval performance which is shown to be the dominant source of retrieval error.
We introduce a low cost, lightweight and compact polarisation sensitive radiometer for the measurement of Cirrus clouds in the submilimeter and far-infrared region (10-50 cm-1). It is widely recognised that enhanced global measurements of cirrus properties are essential to the development of General Circulation and Climate Prediction Models (GCMs) since cirrus clouds have a strong effect on the Earths Global Radiation Budget. We introduce a project currently under development in Cardiff, to design and build a novel instrument suitable for aircraft deployment in order to measure Ice Water Path (IWP) along with cirrus particle size and shape. The radiometer will capitalise on the on going measurements of the NASA led, Fourier Transform interferometer based, Far-Infrared Sensor for Cirrus (FIRSC) instrument for which Cardiff has been closely associated. Data from FIRSC campaigns is being used to select optimum radiometer channels that exhibit good sensitivity to specific cirrus. This new multi-channel radiometer will however have some key advantages over similar spectroscopic instruments for example: portability, increased optical efficiency, a multi-angle field of view and a reduced integration period leading to an improved spatial resolution. The radiometer will benefit from the application of state-of-the-art submm/FIR polariser and solid filter technology currently being developed in Cardiff.
The use of non-focused and focused ion beams as tools for fabrication and assembly of microstructures is described. Non-focused, low energy (< 1.5 keV) and high current density (< 100 mA cm-2) argon ion beams produced by a Kaufman-type source have been used for ultra-precision micromachining of materials for microelectromechanical systems applications. Uniform material removal rates of up to 1 micrometers min-1 without reactive etching are achieved during stencil-mask milling of micro-parts or during pattern transfer into ceramic or semiconductor substrates by photolithography followed by ion milling. Micro-components with typical dimensions in the 1 - 100 micrometers range and having dimensional tolerances of order 0.1 micrometers have been demonstrated, consisting of ultra-thin plates, beams, shafts and cantilevers. Self supporting nickel, aluminium, stainless steel and mu-metal plates with thicknesses down to 1 micrometers have then been used for fabricating more complex micro-parts such as disks, gears and cogs by direct writing using focused ion beam (FIB) micromachining with a resolution of 50 nm. The FIB instrument allows in situ imaging during microfabrication using secondary elements or ions, and can be used for inspection during micro-part assembly. A novel process applicable to the production of 3D micro-parts is also described.