Agilent Measurement Journal - Issue 4 - 2008 - (Page 55)

Existing terahertz imaging and spectroscopy systems typically utilize the technique of free-space time-domain spectroscopy. This offers a limited spatial resolution determined by the diffraction limit of the radiation (of order 1 mm). A number of prototype near-ﬁeld terahertz microscopy systems have been demonstrated based on modiﬁcations of time-domain spectroscopy; however, these have severe operational limitations since they either require powerful optical radiation focused on the sample area — causing damage — or they waste a large portion of the valuable terahertz power by constricting the terahertz beam using an aperture. The objectives of this project are to develop a new microscopy technique with high spatial resolution that aims to overcome these difﬁculties and to perform more systematic studies of the interaction of terahertz radiation with sensitive materials such as biological samples (Figure 2). These properties are read out using an optoelectronic photoconductive measurement scheme that provides a bandwidth extending from a few tens of gigahertz to more than 1 THz. The material property of interest is the high-frequency dielectric constant (refractive index) of the sample being scanned. This property is directly accessed from the size of the shift in the electrical resonance of the band-stop ﬁlter induced by the samples as they are scanned in close proximity to the band-stop ﬁlter (tip). Work over the last year has successfully demonstrated the technique’s proof of principle in scanning semiconductor substrates, allowing it to be optimized for resolution and sensitivity. Agilent Ph.D.s at Leeds Roger Pollard Throughout the course of the relationship with the University of Leeds, there has been Agilent (and previously Hewlett-Packard) support for Ph.D. students at Leeds. Here are four examples of topics that have been the subject of successful Ph.D. theses: • The Design of Microwave and Millimetre-Wave Power Combining Arrays (Andrew Adams) • On-Wafer Microwave Noise Characterization (Caroline Collins) Figure 2. Artist’s impression of new terahertz imaging technique being used to scan a biological substrate. An on-chip waveguide (yellow) directs terahertz radiation into a resonant ﬁlter (blue), whose electrical properties are determined by the surrounding evanescent ﬁeld (red). Scanning the sample produces a contrast map of terahertz effective permittivity. • Network Analyzer Techniques for the Characterization of Lightwave Components (Bala Elamaran) • Optimum Design of Microwave Filters with Finite Dissipation (Andrew Guyette) Much of the work has been published in internationally recognized peer-reviewed journals; some of the technology has found its way into Agilent products; and all of the students are now employed in senior positions in the microwave industry (including some at Agilent). The technology behind the technique can conﬁne terahertz radiation to an active region (a scanning “tip”) that is several tens of square microns in area. The tip, which takes the form of a ﬁlter in a planar on-chip terahertz waveguide, is scanned a small and controllable distance (<1 µm) away from the sample under study. The tip region is highly sensitive to changes in the dielectric permittivity of its surroundings, which alter the tip’s high-frequency electrical properties (its resonant frequency and peak attenuation). Agilent Measurement Journal 55

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 4 - 2008

Agilent Measurement Journal - Issue 4 - 2008 Delivering Confidence through Compliance with Standards Contents Emerging Innovations Trying Early Device Implementations at the IEEE 1588 PlugFest Achieving Greater Confidence in Measurement Accuracy through Consistency in Calibration Services Overcoming the Challenges of RFID Component Testing 3GPP LTE: Introducing Single- Carrier FDMA Ensuring Reliable Operation and Performance in Converged IP Networks Testing Storage Area Networks and Devices at 8.5-Gb/s Fibre Channel Rates Choosing an Appropriate Calibration Method for Vector Network Analysis Making Traceable EVM Measurements with Digital Oscilloscopes Exploring Terahertz Measurement, Imaging and Spectroscopy: The Electromagnetic Spectrum’s Final Frontier Interpreting Quoted Specifications when Selecting Digitizers

Agilent Measurement Journal - Issue 4 - 2008

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