Abstract

We have modeled and demonstrated a scalable, compact, fiber-pumped terahertz source based on difference frequency mixing (DFM) in zinc germanium phosphide (ZGP) capable of producing high average and peak-power pulses. Currently, our terahertz source produces 2mW of average THz power and >40W of peak power with sub-nanosecond pulses at a repetition rate of 100kHz in the range of 2-3THz without cryogenic cooling or ultra-fast optics. This high average power laser-based terahertz output enables the real-time imaging of concealed objects using an off-the-shelf uncooled microbolometer focal-plane array. With this THz system, we have imaged objects obscured inside in a common shipping envelope, demonstrating the potential of compact laser-based terahertz sources for use in security screening applications.

© 2007 Optical Society of America

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References

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  1. Y. Chen et al., "THz diffuse reflectance spectra of selected explosives and related compounds," in Terahertz for Military and Security Applications, edited by R. Jennifer Hwu, Dwight L. Woolard, Mark J. Rosker, Proceedings of the SPIE 5790 (SPIE, Bellingham, WA), May 2005.
  2. JasonC.  Dickinson et al., "Terahertz imaging of subjects with concealed weapons," in Terahertz for Military and Security Applications IV, edited by Dwight L. Woolard, R. Jennifer Hwu, Mark J. Rosker, James O. Jensen, Proceedings of the SPIE 6212 (SPIE, Bellingham, WA, 2006), May 2006.
    [CrossRef]
  3. A. W. M. Lee and Q. Hu, "Real-time, continuous-wave terahertz imaging by use of a microbolometer focal-plane array," Opt. Lett. 30, 2563-2565 (2005).
    [CrossRef] [PubMed]
  4. A. W. M. Lee et al., "Real-time terahertz imaging over a standoff distance (>25 meters)," Appl. Phys. Lett. 89 (2006).
    [CrossRef]
  5. R. M. Langdon et al., "Military applications of terahertz imaging," presented at the First Electro Magnetic Remote Sensing Defence Technology Centre Conference, Edinburgh, Scotland, 2004.
  6. G. Chang et al., "Power scalable compact THz system based on an ultrafast Yb-doped fiber amplifier," Opt. Express 14, 7909-7913 (2006). http://www.opticsinfobase.org/abstract.cfm?id=97680.
    [CrossRef] [PubMed]
  7. K. L. Vodopyanov et al., "Terahertz-wave generation in quasi-phase-matched GaAs," Appl. Phys. Lett. 89 (2006).
    [CrossRef]
  8. W. Shi and Y. J. Ding, "Continuously tunable and coherent terahertz radiation by means of phase-matched difference-frequency generation in zinc germanium phosphide," Appl. Phys. Lett. 83, 848-850 (2003).
    [CrossRef]
  9. W. Shi et al., "Coherent terahertz waves based on difference-frequency generation in an annealed zinc-germanium phosphide crystal: improvements on tuning ranges and peak powers," Opt. Commun. 233, 183-189 (2004).
    [CrossRef]
  10. W. Shi, Y. J. Ding,  et al., "Efficient, tunable, and coherent 0.18-5.27-THz source based on GaSe crystal," Opt. Lett. 27, 1454-1456 (2002).
    [CrossRef]
  11. W. Shi and Y. J. Ding, "Tunable terahertz waves generated by mixing two copropagating infrared beams in GaP," Opt. Lett. 30, 1030-1032 (2005).
    [CrossRef] [PubMed]
  12. G. L. Carr et al., "High-power terahertz radiation from relativistic electrons," Nature 420, 153 (2002).
    [CrossRef] [PubMed]
  13. D. Creeden et al., "Near diffraction-limited, 1064nm, all-fiber master oscillator fiber amplifier (MOFA) with enhanced SRS suppression for pulsed nanosecond applications," presented at the 2006 SSDLTR, Albuquerque, NM, June 13-15, 2006, Paper FIBER1-4.
  14. D. Creeden et al., "Fiber laser transmitter for LADAR applications," presented at the 2006 Meting of the MSS Specialty Group on Active E-O Systems, Monterey, CA, 2006.
  15. V. G. Dmitriev et al., Handbook of Nonlinear Optical Crystals, A. E. Siegman, ed. (Springer-Verlag, New York, NY, 1999).
  16. R. L. Sutherland, Handbook of Nonlinear Optics, B. J. Thompson, ed. (Marcel Dekker, Inc., New York, NY, 1996).

2006

K. L. Vodopyanov et al., "Terahertz-wave generation in quasi-phase-matched GaAs," Appl. Phys. Lett. 89 (2006).
[CrossRef]

A. W. M. Lee et al., "Real-time terahertz imaging over a standoff distance (>25 meters)," Appl. Phys. Lett. 89 (2006).
[CrossRef]

G. Chang et al., "Power scalable compact THz system based on an ultrafast Yb-doped fiber amplifier," Opt. Express 14, 7909-7913 (2006). http://www.opticsinfobase.org/abstract.cfm?id=97680.
[CrossRef] [PubMed]

2005

2004

W. Shi et al., "Coherent terahertz waves based on difference-frequency generation in an annealed zinc-germanium phosphide crystal: improvements on tuning ranges and peak powers," Opt. Commun. 233, 183-189 (2004).
[CrossRef]

2003

W. Shi and Y. J. Ding, "Continuously tunable and coherent terahertz radiation by means of phase-matched difference-frequency generation in zinc germanium phosphide," Appl. Phys. Lett. 83, 848-850 (2003).
[CrossRef]

2002

Carr, G. L.

G. L. Carr et al., "High-power terahertz radiation from relativistic electrons," Nature 420, 153 (2002).
[CrossRef] [PubMed]

Chang, G.

Ding, Y. J.

Hu, Q.

Lee, A. W. M.

A. W. M. Lee et al., "Real-time terahertz imaging over a standoff distance (>25 meters)," Appl. Phys. Lett. 89 (2006).
[CrossRef]

A. W. M. Lee and Q. Hu, "Real-time, continuous-wave terahertz imaging by use of a microbolometer focal-plane array," Opt. Lett. 30, 2563-2565 (2005).
[CrossRef] [PubMed]

Shi, W.

W. Shi and Y. J. Ding, "Tunable terahertz waves generated by mixing two copropagating infrared beams in GaP," Opt. Lett. 30, 1030-1032 (2005).
[CrossRef] [PubMed]

W. Shi et al., "Coherent terahertz waves based on difference-frequency generation in an annealed zinc-germanium phosphide crystal: improvements on tuning ranges and peak powers," Opt. Commun. 233, 183-189 (2004).
[CrossRef]

W. Shi and Y. J. Ding, "Continuously tunable and coherent terahertz radiation by means of phase-matched difference-frequency generation in zinc germanium phosphide," Appl. Phys. Lett. 83, 848-850 (2003).
[CrossRef]

W. Shi, Y. J. Ding,  et al., "Efficient, tunable, and coherent 0.18-5.27-THz source based on GaSe crystal," Opt. Lett. 27, 1454-1456 (2002).
[CrossRef]

Vodopyanov, K. L.

K. L. Vodopyanov et al., "Terahertz-wave generation in quasi-phase-matched GaAs," Appl. Phys. Lett. 89 (2006).
[CrossRef]

Appl. Phys. Lett.

A. W. M. Lee et al., "Real-time terahertz imaging over a standoff distance (>25 meters)," Appl. Phys. Lett. 89 (2006).
[CrossRef]

K. L. Vodopyanov et al., "Terahertz-wave generation in quasi-phase-matched GaAs," Appl. Phys. Lett. 89 (2006).
[CrossRef]

W. Shi and Y. J. Ding, "Continuously tunable and coherent terahertz radiation by means of phase-matched difference-frequency generation in zinc germanium phosphide," Appl. Phys. Lett. 83, 848-850 (2003).
[CrossRef]

Nature

G. L. Carr et al., "High-power terahertz radiation from relativistic electrons," Nature 420, 153 (2002).
[CrossRef] [PubMed]

Opt. Commun.

W. Shi et al., "Coherent terahertz waves based on difference-frequency generation in an annealed zinc-germanium phosphide crystal: improvements on tuning ranges and peak powers," Opt. Commun. 233, 183-189 (2004).
[CrossRef]

Opt. Express

Opt. Lett.

Other

D. Creeden et al., "Near diffraction-limited, 1064nm, all-fiber master oscillator fiber amplifier (MOFA) with enhanced SRS suppression for pulsed nanosecond applications," presented at the 2006 SSDLTR, Albuquerque, NM, June 13-15, 2006, Paper FIBER1-4.

D. Creeden et al., "Fiber laser transmitter for LADAR applications," presented at the 2006 Meting of the MSS Specialty Group on Active E-O Systems, Monterey, CA, 2006.

V. G. Dmitriev et al., Handbook of Nonlinear Optical Crystals, A. E. Siegman, ed. (Springer-Verlag, New York, NY, 1999).

R. L. Sutherland, Handbook of Nonlinear Optics, B. J. Thompson, ed. (Marcel Dekker, Inc., New York, NY, 1996).

R. M. Langdon et al., "Military applications of terahertz imaging," presented at the First Electro Magnetic Remote Sensing Defence Technology Centre Conference, Edinburgh, Scotland, 2004.

Y. Chen et al., "THz diffuse reflectance spectra of selected explosives and related compounds," in Terahertz for Military and Security Applications, edited by R. Jennifer Hwu, Dwight L. Woolard, Mark J. Rosker, Proceedings of the SPIE 5790 (SPIE, Bellingham, WA), May 2005.

JasonC.  Dickinson et al., "Terahertz imaging of subjects with concealed weapons," in Terahertz for Military and Security Applications IV, edited by Dwight L. Woolard, R. Jennifer Hwu, Mark J. Rosker, James O. Jensen, Proceedings of the SPIE 6212 (SPIE, Bellingham, WA, 2006), May 2006.
[CrossRef]

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Figures (3)

Fig. 1.
Fig. 1.

Schematic of the terahertz system architecture including the fiber-pump setup, terahertz conversion crystal, optics, and detector.

Fig. 2.
Fig. 2.

Average THz output power vs. total incident pump power for a 2.45THz (122μm) output signal. Solid line: theoretical model based on (1), data points: experimental measurements. Total incident pump power refers to the sum of the average 1055nm and 1064.2nm pump powers incident on the crystal face. In the experiment and the model, these pump powers were set to be equal, each with a 100kHz repetition rate and 700ps pulse width.

Fig. 3.
Fig. 3.

Pictures of objects used in THz imaging and false-color images of those objects concealed in a shipping envelope using the terahertz system; (a) razor blade, (b) imaged razor blade inside envelope, (c) knife, (d) imaged knife inside envelope, (e) fiberglass knife, (f) imaged fiberglass knife inside envelope.

Equations (1)

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η = 2 ω i 2 d eff 2 L 2 I p 2 T p 1 T p 2 T i ε 0 c 3 n o ( λ p 1 ) n e ( λ p 2 , θ ) n e ( λ i , θ ) sin c 2 ( Δ k L 2 ) e ( α i L ) 1 + e Δα L 2 e 1 2 Δα L cos ( Δ KL ) ( Δ kL ) 2 + ( 1 2 Δα L ) 2

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