CEOI Emerging Technologies Workshop Heterodyne Technologies 29 th January 2008

1. CEOI Emerging Technologies WorkshopHeterodyne Technologies29th January 2008 Dave Matheson Millimetre Technology RAL Space Science and Technology Department

2. Contents • Introduction • Technology status • EO opportunities • Laser Heterodyne Radiometry - (Damien Weidmann, Kevin Smith)

3. mm-wave limb spectra co-located 0.75mm limb imager Cloud opaque in IR & near-IR limb-views BT (K) Frequency (GHz) Introduction • Frequency range: • ~200 to >3,000GHz: • Rich in rotational and rotation-vibration transitions of molecular species • Dielectric materials that are partially transparent to the radiation • Part of the spectrum still to be fully exploited: • Technology and applications are still being invented and improved • Why Heterodyne technology? - sensitive detection, arbitrarily fine spectral resolution Results from the MARSCHALS airborne instrument, demonstrating mm wave observations of H2O & O3 through tropical cirrus

4. Spectrometer RF feedhorn f1 IF Amplifier f2 mixer fn Local Oscillator Source Status of Heterodyne Technology • Planar diode receivers have been demonstrated at all frequencies up to ~3THz: • Schottky diode mixer technology for room temperature operation • Cryogenic mixers for lowest noise performance • Air filled, single moded waveguide for critical technology (mixers, LO sources) : • circuits can now be accurately simulated and manufactured using non-linear design software & CNC mills • Generation of THz LO power remains tricky: • Development of receiver arrays will benefit from better LO technology • Commercial availability of components & circuitry > ~300GHz is improving with time • Indicative heterodyne radiometer performance • RAL 380 GHz waveguide diode mixer Queen’s University Belfast/ASTRIUM dielctric-free mm filter

5. Technology Trends • Future instruments will require increased spectral coverage, lower resource requirements (mass and power), and receiver array • This application demand is driving technology in directions that include the following: • Higher frequency components (mixers, harmonic multipliers) - above 1THz • More sophisticated components (Image reject sideband mixers, balanced mixers…) • New methods of THz power generation (for LOs): • Quantum Cascade Lasers (QCL) • Photonic mixing (optical down conversion) • Increased circuit integration: • Reduced mass, improved reliability, simpler interfaces, lower cost • New concepts for building focal plane arrays - specifically, provision and injection of LO to drive multiple mixers • Prototype IRAM array technology (Huggard et al.)

6. Conversion Loss Frequency Technology Trends (Examples) Diode region RF signal waveguide ~200 GHz Integrated mixers • Fixed tuned waveguide mixer cavity • Single 50micron thick GaAs circuit (filters and diodes) Integrated Mixer circuit detail 340GHz Single Sideband Mixer (CEOI) LO waveguide • Circuit design and simulation (Thomas et al.)

7. Opportunities • Investigation of processes linking atmospheric composition and climate • Future assimilation into operational systems used to forecast weather & air quality • In the short/medium term: • STEAM-R, limb sounder focused on UT: • Opportunity for UK involvement in Swedish funded contribution to PREMIER • CEOI studies to define instrument requirements and demonstrate novel SSB mixer technology (Astrium, RAL, QU Belfast, SULA, ) • Aircraft radiometer designed to discriminate cirrus size components intermediate between those accessible in the IR and microwave: • CEOI studies to demonstrate LO source and channel separating (filter) technology (Astrium, RAL, QUB) • Linked studies with UKMO (FAAM) and ESA (aircraft demonstrator) STEAM Antenna and optics model (CEOI - Astrium)

8. Quantum Cascade Laser Heterodyne Radiometer (LHR) • Key capabilities • Passive monitoring of emissions and air quality – Occultation capability • Offers combination of high spectral & spatial resolutions at high sensitivity • Based on solid-state mid-IR quantum cascade lasers (QCLs) • Quantum cascade lasers as local oscillators • - High power ( >10 mW ) • Band engineering to tailor central wavelength from 4 to 150 mm • Compact and robust for field deployment • High spectral purity (~ 1 MHz) • Continuously frequency tuneable (1% of central frequency) • Existing prototype developed at RAL • - Operates at 9.7 mm to target atmospheric ozone • Spectral resolution from 0.001 to 0.2 cm-1 set by electronic filters • 75 x 75 cm2 portable breadboard • Wide range of prospects • - Ultra-compact packaging through optical integration • - Extension to the far infrared and terahertz frequency range • - Wide wavelength coverage with external cavity laser implementation • Heterodyne imaging through development of arrays of mixers • Development of heterodyne LIDAR

9. Quantum Cascade Laser Heterodyne Radiometer (LHR) Retrieved O3 profile Example high-resolution atmospheric spectra Spectra spanning 2 cm-1, Resolution 220 MHz DSB • Currently being implemented for CEOI Phase 1 • - Thermal and electro-magnetic shielding • - Enhanced laser optical isolation • - Frequency calibration investigation and active baseline correction • - Absolute radiometric calibration • - Further ground-based field deployment • - Performance analysis for different viewing modes and various platforms types

10. Summary • THz and IR heterodyne technology and applications are still being invented • Strong technology base in the UK in Industry, SMEs and Universities • Excellent opportunity to exploit programmes proposed for EU/ESA GMES Sentinel and Eumetsat post-EPS satellite missions: • KE applications, e.g., THz security imaging • CEOI is supporting critical technology development: • Aimed at PREMIER STEAM-R • Cirrus aircraft instrument • SSB Mixers, frequency multipliers, optical filters • Associated ESA TRP/GSTP funding: • Wideband spectrometer development, Cirrus aircraft instrument studies THz security imaging, ThruVision