Laser light sources that are currently used in two-photon microscopy produce photons that have random spreads in both time and space, requiring large intensities to accidentally place two photons within a small enough volume to cause excitation. However, entangled light is intrinsically paired within a very small time window and a very small angular extent. We are working on the development of a microscope that makes use of entangled-photon pairs as an excitation source. This technique is expected to have a potential advantage over conventional two-photon fluorescence microscopy: the ability to access narrow upper energy levels. Calculations of the entangled-photon pair absorption cross-section reveals that entangled-photon absorption is fundamentally different from the usual two-photon absorption, and offers the possibility of carrying out novel spectroscopic measurements. Entangled-photon fourth-order interference effects can also be used to carry out range measurements to determine the structure of biological and physical media via a technique called quantum optical coherence tomography (QOCT). Such measurements are similar to those currently obtained by the use of optical coherence tomography (OCT), but with the added advantage of even-order dispersion cancellation.

1. Dispersion-cancelled and dispersion-sensitive quantum optical coherence tomography
   M. B. Nasr, B. E. A. Saleh, A. V. Sergienko, and M. C. Teich
   Opt. Express 12, 1353-1362 (2004). [PDF]
   
   
2. Polarization-sensitive quantum-optical coherence tomography
   M. C. Booth, G. Di Giuseppe, B. E. A. Saleh, A. V. Sergienko, and M. C. Teich
   Phys. Rev. A 69, 043815 (2004). [PDF]
   
   
3. Demonstration of dispersion-canceled quantum-optical coherence tomography
   M. B. Nasr, B. E. A. Saleh, A. V. Sergienko, and M. C. Teich
   Phys. Rev. Lett. 91, 083601 (2003). [PDF]
   
   
4. Quantum optical coherence tomography with dispersion cancellation
   A. F. Abouraddy, M. B. Nasr, B. E. A. Saleh, A. V. Sergienko, and M. C. Teich
   Phys. Rev. A 65, 053817 (2002). [PDF]
   
   
5. Entangled-photon Fourier optics
   A. F. Abouraddy, B. E. A. Saleh, A. V. Sergienko, and M. C. Teich
   J. Opt. Soc. Am. B 19, 1174-1184 (2002). [PDF]
   
   
6. Biphoton focusing for two-photon excitation
   M. B. Nasr, A. F. Abouraddy, M. C. Booth, B. E. A. Saleh, A. V. Sergienko,
   M. C. Teich, M. Kempe, and R. Wollenschensky
   Phys. Rev. A 65, 023816 (2002). [PDF]
   
   
7. Role of entanglement in two-photon imaging
   Ayman F. Abouraddy, Bahaa E. A. Saleh, Alexander V. Sergienko,
   and Malvin C. Teich
   Phys. Rev. Lett. 87, 123602 (2001). [PDF]
   
   
8. Entangled-photon virtual-state spectroscopy
   B. E. A. Saleh, B. M. Jost, H.-B. Fei, and M. C. Teich,
   Phys. Rev. Lett.  80, 3483-3486 (1998). [PDF]
   
   
9. Multiphoton absorption cross section and virtual-state spectroscopy for the entangled n-photon state
   J. Perina, Jr., B. E. A. Saleh, and M. C. Teich
   Phys. Rev. A  57, 3972-3986 (1998). [PDF]
   
   
10. Multiphoton absorption cross section for the entangled n-photon state
    J. Perina, Jr., B. E. A. Saleh, and M. C. Teich
    Proc. Fifth Int. Conf. Squeezed States and Uncertainty Relations,
    edited by D. Han, J. Janszky, Y. S. Kim, and V. I. Man'ko
    (NASA Conference Publication No. 1998-206855, NASA Goddard, Greenbelt, MD, 1998), pp. 459-466.
    
    
11. Entanglement-induced two-photon transparency
    H. B. Fei, B. M. Jost, S. Popescu, B. E. A. Saleh, M. C. Teich
    Phys. Rev. Lett. 78, 1679-1682 (1997). [PDF]
    
    
12. Mikroskopie s kvantove provázanimi fotony
    (Microscopy with quantum-entangled photons)
    M. C. Teich and B. E. A. Saleh
    Ceskoslovenski casopis pro fyziku 47, 3-8 (1997). [PDF]