Terahertz imaging and quantum cascade laser based devices

The terahertz (THz) frequency range (f=0.3-10 THz, [lambda]=30-1000 lam) is much less technologically developed that the adjacent microwave and infrared frequency ranges, but offers several advantages for imaging applications: THz wavelengths offer better spatial resolutions than microwave frequencies, and THz radiation is able to penetrate materials that are opaque at infrared frequencies (e.g. packaging, plastics, paints and semiconductors). These features, combined with the unique THz spectral signatures of chemicals have lead to the development of terahertz imaging systems for non-destructive test. However, the weak radiation sources in these existing systems result in single pixel scanning architectures requiring minutes to acquire images or enhanced speed at the expense of signal to noise ratio (SNR). In this thesis, a system for real-time imaging is demonstrated using recently developed terahertz quantum-cascade laser (QCL) sources, along with commercial, focal plane array thermal detectors. The system uses a high power (48 mW) 4.3-THz QCL, which is also used to characterize the focal plane array, resulting in a noise equivalent power (NEP) of 320 pW/Hz. The source and detector are used in a synchronous detection scheme, resulting in an SNR of ~25 dB/pixel at a 20-Hz frame rate. This represents a two order of magnitude improvement in speed over previous systems at comparable SNRs. Real-time imaging over a 25-m distance is described, using a QCL adjusted for emission in the narrow 4.9 THz atmospheric transmission window.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2010

Author dc:creator

• Lee, Alan Wei Min

Advisor dc:contributor.advisor

• Qing Hu.

• Electrical Engineering and Computer Science.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/58175

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/58175