Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2003-02-12
2004-04-20
Gagliardi, Albert (Department: 2828)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S330000, C250S340000
Reexamination Certificate
active
06723991
ABSTRACT:
BACKGROUND OF THE INVENTION
Systems are known in which ultrashort laser pulses are used to generate and coherently detect terahertz (THz) radiation. Most types of THz systems use single laser pulses to generate broad-band THz radiation. Time-domain, terahertz spectroscopy has been shown to provide a useful analytical tool for measuring properties of molecular vapors, both pure and in mixture with other gases, such as air (see M. van Exter, et al., Optics Letters, Vol 14, p. 1128 (1989)). The use of THz radiation reveals certain features which are not afforded by the use of laser radiation lying in the “usual” range of 200 nm to 10 microns.
X. -C. Zhang et al., teach a THz sensing system which employs electro-optic crystals, such as ZnTe, to serve as THz receivers, these having the advantage of higher detection bandwidth (see Q. Wu and(X. -C. Zhang, Appl. Phys. Lett, Vol 67, p. 2523 (1995)). The generation of narrow-band THz radiation can give significant advantages over broadband THz generation in certain spectroscopic applications. Continuous wave narrow-band THz radiation can be generated and detected by photomixing two CW lasers in a THz transceiver, such as a photoconductive antenna, as demonstrated by Verghese et al. (see S. Verghese, et al., Appl. Phys. Lett, Vol. 73, p. 3824 (1998)). Moderately narrow-band THz bursts can be generated by exciting a THz emitter with a train of optical pulses spaced to the desired THz frequency as taught by Siders et al. (see C. W. Siders, et al., Opt. Lett., Vol 24, p. 241 (1999)), and Weling et al. who excites a semiconductor surface (see A. S. Weling, et al., Appl. Phys. Lett, Vol. 64, p. 137 (1994)). Alternatively, Norris demonstrates a method in which a single laser pulse can be used to generate narrow-band THz radiation directly by optical rectification in a periodically poled nonlinear crystal such as PPLN (periodically poled lithium niobate), by exploiting the group-velocity walkoff between the optical pulse and the THz radiation in the crystal (see T. -S. Lee, T. Meade, V. Perlin, H. Winful, T. B. Norris, A. Galvanauskas, “Generation of narrow-band terahertz radiation via optical rectification of femtosecond pulses in periodically poled lithium niobate,” Appl. Phys. Lett., Vol. 76, p. 2505 (2000)). In another method which does not employ ultrafast lasers, T. Heinz et al. teach a THz generation/detection system employing two detuned CW lasers to generate THz radiation at the beat frequency between the two lasers (see A. Nahatha, James T. Yardley, Tony, F. Heinz, “Free-space electro-optic detection of continuous-wave terahertz radiation,” Appl. Phys. Lett., Vol. 75, p. 2524 (1999)). The same two lasers activate the THz receiver, providing narrow-band coherent detection. This system provides very narrow-band THz radiation with ~MHz linewidths, limited only by the absolute frequency stability of the two CW lasers, and have potential for linewidths less than 1 kHz.
CW heterodyne methods provide superior frequency resolution in the THz measurement system, however suffer the drawbacks of very low efficiency, as well as fringe ambiguity. While these systems can give sub-wavelength resolution, the larger scale TOF (time-of-flight) information is lost. The use of ultrashort pulses to generate and detect THz radiation provides useful TOF information. Furthermore, the use of ultrashort pulses can ultimately result in greater efficiency of THz emission, especially in cases such as that demonstrated by Norris, where the optical pulse is re-used many times in the generation process. As extensions of the THz sensing technology, various systems have been devised which combine THz generation/detection with imaging to give imaging in the THz frequency range. B. Hu et al. teach a THz imaging system which uses single, broad-band THz pulses repetitively while the sample under test is raster scanned through the THz beam (see B. B. Hu and M. C. Nuss, Appl. Phys. Lett, Vol. 20, p. 1716 (1995); see U.S. Pat. No. 5,623,145; and see U.S. Pat. No. 5,710,430). Because this system relies on THz waveform measurement, time delay scanning was required in addition to the raster scanning, both techniques, in turn, requiring the use of a large number of laser shots to complete the measurement even if no signal averaging was used. This type of system generally requires at least several minutes to complete an imaging measurement. Additionally, if spectral information about the image is desired, then complex signal analysis such as Fourier or wavelet transforms are required. A system for performing THz imaging with a single laser shot was first demonstrated by Q. Wu et al. This system works by using an EO field sensor crystal to impart THz image information on an optical beam (an ultrashort laser pulse), and then imaging the optical beam with an optical imaging device such as a CCD camera (see Q. Wu, T. D. Hewitt, and X. -C. Zhang, Appl. Phys. Lett., Vol. 69, 1026 (1996)).
SUMMARY OF THE INVENTION
The current invention combines advantages of tunable narrow-band THz generation and coherent detection, with the unique properties of ultrashort pulses, those being single-shot capability, TOF information, high pulse intensity, and greater efficiency of THz generation. The current invention provides the additional advantage of using two THz frequencies to give a differential measurement providing greatly enhanced sensitivity and immunity to laser fluctuations. Additionally, the narrowband THz emission can be adapted to single-shot THz imaging systems, which commonly use only a single, broadband THz pulse.
REFERENCES:
patent: 5623145 (1997-04-01), Nuss
patent: 5710430 (1998-01-01), Nuss
Martin van Exter, et al.,Terahertz time-domain spectroscopy of water vapor, Optics Letters, vol. 14, No. 20, p. 1128-1130 (Oct. 15, 1989).
Q. Wu and X.C. Zhang,Free-space electro-optic smapling of terahertz beams, Appl. Phys. Letters, vol. 67, p. 3523-3525 (Dec. 11, 1995).
S. Verghese, et al,Generation and detection of coherent terahertz waves using two photomixers, Appl. Phys. Letters, vol. 73, No. 26, p. 3824-3826 (Dec. 28, 1998).
A.S. Weling, et al.,Generation of tunable narrow-band THz radiation from large aperture photconducting antennas, Appl. Phys. Lett., vol. 67, p. 137-139 (Jan. 10, 1994).
N.M. Froberg, et al.,Generation of steerable submillimeter waves from semiconductor surfaces by spatial light modulators, Appl. Phys. Lett. vol. 59, p. 768-770 (Aug. 12, 1991).
Y.S. Lee, et al.,Generation of narrow-band terahertz radiation via optical rectification of femtosecond pulses in periodically poled lithium niobate, Appl. Phys. Lett., vol. 76, No. 18, p. 2505-2507 (May 1, 2000).
Ajay Nahatha, et al.,Free-space electro-optic detection of continuous-wave terahertz radiation, Appl. Phys. Lett., vol. 75, No. 17, p. 2524-2526 (Oct. 25, 1999).
B.B. Hu and M.C. Nuss,Imaging with terahertz waves, Appl. Phys, Lett, vol. 20, No. 16, p. 1716-1718 (Aug. 15, 1995).
Q. Wu, et al.,Two-dimensional electro-optic imaging of THz beams, Appl. Phys. Lett., vol. 69, p. 1026-1028 (Aug. 19, 1996).
G. Imeshev, et al.,Engineerable femtosecond pulse shaping by second-harmonic generation with Fourier synthetic quasi-phase-matching gratings, Opt. Lett., vol. 23, No. 11, p. 864-866 (1998).
C.W. Siders, et al,Generation and characterization of terahertz pulse trains from biased, large-aperture photconductors, Opt. Lett., vol. 24, No. 4, p. 241-243 (Feb. 15, 1999).
Richard K. Lai, et al,A photoconductive, miniature terahertz source, Appl. Phys. Letter, vol. 72, No. 24, p. 3100-3102 (Jun. 15, 1998).
Q. Wu et al., “Free-space electro-optic sampling of terahertz beams”, Appl. Phys. Lett. vol. 67, No. 24, Dec. 11, 1995, pp. 3523-3525.
S. Verghese et al., “Generation and detection of coherent terahertz waves using two photomixers”, Appl. Phys. Lett. vol. 71, No. 26, Dec. 28, 1998, pp. 3824-3826.
A.S. Weiling, et al, “Generation of tunable narrow-band THz radiation from large aperture photoconducting antennas”, Appl. Phys. Lett. vol. 64, No. 2, Jan. 10, 1994, pp. 137-139.
X-C. Zhang et al, “Generation of steerable submillimete
Galvanauskas Almantas
Harter Donald J.
Sucha Gregg D.
Gagliardi Albert
Imra America Inc.
LandOfFree
Single-shot differential spectroscopy and spectral-imaging... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Single-shot differential spectroscopy and spectral-imaging..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Single-shot differential spectroscopy and spectral-imaging... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3259737