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56. History of Research in Nonlinear Optics at the Institute of Optics

56. History of Research in Nonlinear Optics at the Institute of Optics

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56. History of Research in Nonlinear at

Robert W. Boyd

Although the birth of the field of is often taken to be the first observation of second- by Franken et al. in 1961 [1], in fact the rudiments of this field started much earlier. Parts of this early history can be traced back to work performed at The Institute of Optics, and research in nonlinear optics has thrived at the Institute ever since. The earliest report of a nonlinear optical effect known to the author is that of G. N. Lewis, who in 1941 reported saturation with increasing excitation strength of the fluores- cence intensity of the organic dye fluorescein in a boric acid glass host [2]. In fact, the author with his students Mark Kramer and Wayne Tompkin became very much intrigued by this material system, and in the 1980s developed fluorescein-doped boric acid glass as a highly nonlinear material for use in phase conjugation and other applications [3]. At the risk of digression, it should be noted that G. N. Lewis was one of the most gifted chemists in the United States in the first half of the twentieth century. He held faculty positions at Harvard, at MIT, and at the University of California, Berkeley. Early in his career, Lewis developed the idea that the sharing of paired electrons leads to the formation of a chemi- cal bond. The notion of a Lewis acid (a substance such as the Hϩ ion that can accept a pair of nonbonding electrons) and a Lewis base (a substance such as the OHϪ ion that can donate a pair of nonbonding electrons) follows directly from this idea. Moreover, it was Lewis who introduced the word “” into the scientific lexicography [4]. Until his time, were known as “quanta” of radiation, a term introduced by Planck. So Professor Lewis not only introduced the modern definition of an acid and a base, but also invented the word “photon” and created the field of nonlinear optics. Work in nonlinear optics at The Institute of Optics can be traced back to the work of Brian O’Brien during the Second World War. O’Brien had directed a number of research efforts aimed at helping the U.S. war effort, described elsewhere in this volume. One such effort, under the immediate supervision of Franz Urbach, involved the development of phosphors that would emit visible upon excitation by infrared radiation. These phos- phors led to the development of various infrared and low-light image converters that were crucial to the U.S. war effort. But an additional application involved the utilization of the nonlinear transfer characteristics of these phosphors. A problem facing the U.S. Navy was that the Japanese were making their bombing attacks on U.S. ships by approaching from the direction of the sun, thus effectively blinding those defending their ships. An imaging device was needed that would dramatically reduce the brightness of the sun while pre- serving the brightness of immediately adjacent objects. O’Brien and his associates solved this problem through use of saturation of the luminescence of their phosphors. Strong saturation of the luminescence efficiency occurred at those regions illuminated by the sun; AJC-07.qxd 21/06/04 11:22 AM Page 294

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Assistant Professor Mike Hercher discusses possible experiments to test Associate Professor Al Gold’s theory.

little or no saturation occurred at the adjacent regions, allowing objects in these regions, such as enemy aircraft, to be clearly seen. This device became know as the Icaroscope, named after the Greek tragic hero Icarus. The invention of the laser led to dramatically new possibilities in the field of nonlin- ear optics. A spectacular example is the observation at The Institute of Optics in 1964 by Michael Hercher of bulk, laser-induced damage of optical materials such as glass [5]. This observation is at first sight surprising (both in 1964 and today), because a simple estimate of the intensity of the incident laser light suggests that no damage should occur. The current explanation of the phenomenon discovered by Hercher is that, as a consequence of the nonlinear optical process of self-focusing, the laser beam collapsed to a very small spot size upon entering the material. The intensity at the focal spot thus created can be many orders of magnitude larger than that of the incident laser beam. Hercher’s discovery has thus through time led to the development of diverse sub-fields of nonlinear optics including self-focusing, optical formation, and the laser processing of materials. Theoretical work was also stimulated by the development of the laser. Joseph Eberly investigated nonlinear behavior of a free electron in the field of a laser beam and predicted a nonlinear contribution to the Compton wavelength shift [6]. In addition, Barry Bebb and Albert Gold developed one of the earliest theories of multiphoton absorption of laser light [7]. The author of this essay joined the faculty of the Institute in 1977. Michael Raymer joined the faculty soon thereafter, and the pair, along with Donald Harter, began conducting detailed theoretical and experimental studies of how four-wave mixing processes become modified in the presence of laser fields so intense that the atomic level struc- ture is modified by the light field [8, 9]. They found that under these circumstances the laser beam transmitted through an atomic vapor cell tends to develop a ring structure surrounding the central component; this process has been called conical emission and has subsequently been investigated extensively. Raymer and his student Ian Walmsley (who later spent many years on the optics faculty) performed detailed theoretical and experimental studies of how the process of stimulated is initiated by quantum noise [10]. This work motivated AJC-07.qxd 21/06/04 11:22 AM Page 295

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Institute visitors Paul Narum and Kazimierz Rzazewski to perform similar studies of the initiation of the process of stimulated [11]; these predictions are useful in predicting the properties of phase conjugate based on stimulated Brillouin scattering. Dennis Hall also joined the faculty of the Institute at about this same time. His primary research interest was in guided-wave optics, although some of his research was in the field of nonlinear optics. For example, he and Theodore Dziura worked on optical bistability in various photonic systems [12]. My own research has been in the field of optical physics with a concentration on fundamental and applied nonlinear optics. The fundamentals of this field are presented in my textbook Nonlinear Optics [13]. During my years in Rochester, I have had the pleasure of supervising and interacting with a large number of exceptional Ph.D. students during my years at the Institute. The remainder of this article outlines some of the results of our research studies.

Local Field Effects and Artificial Materials for Nonlinear Optics

My students, co-workers, and I have performed fundamental studies of the nature of local field effects in dense optical materials, and have shown that local field effects can be exploited to synthesize engineered materials with specially tailored nonlinear . This work commenced with a laboratory study by Jeffrey Maki, Michelle Malcuit, John Sipe, and myself of local field effects in a dense atomic vapor. The influence of local field effects was controlled in this experiment by continuously varying the atomic number density. A key result of this project was the first measurement [14] of the Lorentz red shift, a shift of the atomic absorption line as a consequence of local field effects. This red shift had been predicted by Lorentz in the latter part of the nineteenth century, but had never previously been observed experimentally. In addition to confirming this century-old pre- diction, this work is significant in confirming the validity of the Lorentz local-field formal- ism even under conditions associated with the resonance response of atomic vapors. More recently, we have made use of local field effects to tailor the nonlinear opti- cal response of composite optical materials. This work includes the prediction [15] and subsequent laboratory confirmation by George Fischer, Russell Gehr, and others [16] that it is possible to construct a composite material in such a manner that the nonlinear susceptibility of the composite exceeds those of the materials from which it is con- structed. A three-fold enhancement of the nonlinear susceptibility has been demonstrated more recently through use of this technique by Robert Nelson and myself [17]. Composite materials hold promise for even larger values of the enhancement in materials formed of alternating metallic and layers forming a photonic bandgap structure, as shown by Ryan Bennink and others [18]. Quite recently, we have become interested in forming completely artificial materials by coupling micro-ring resonators to optical waveguides. This work is based on the realization that the nonlinear response and dispersive properties of a ring resonator increase very rapidly with the finesse of the res- onator. John Heebner has constructed working devices of this sort as part of his thesis work [19, 20]. AJC-07.qxd 21/06/04 11:22 AM Page 296

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Dan Gauthier and Bob Boyd study nonlinear optics of sodium vapor.

Optical Studies of Chaos, Nonlinear Dynamics, and Optical

We were also involved in some of the early studies of optical chaos and optical nonlinear dynamics [21]. Our group performed the first laboratory demonstrations of chaotic behav- ior in a purely passive, resonatorless nonlinear optical system. This work was crucial in elucidating the conditions under which an optical system could become unstable to chaotic behavior; prior to that time optical chaos had been observed only in and in passive nonlinear optical systems in the presence of external feedback. Our work entailed the obser- vation by Daniel Gauthier, Narum, and myself of chaotic behavior in a photorefractive phase conjugate [22]. Our work also involved the prediction by Alexander Gaeta and others [23] and subsequent observation by Gauthier, Malcuit, and myself of chaotic behavior in the polarizations of counterpropagating laser beams in an atomic sodium vapor [24]. More recently, we have become involved in research on spontaneous pattern formation AJC-07.qxd 21/06/04 11:22 AM Page 297

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in nonlinear optical systems, leading to the observation and theoretical description of hon- eycomb patterns and other regular patterns formed spontaneously in a laser beam propa- gating through an atomic sodium vapor [25].

Fundamental Studies in Quantum and Nonlinear Optics

Malcuit, Maki, David Simkin and I conducted a successful experiment [26] aimed at elucidating the relationship between superfluorescence and amplified spontaneous emission (ASE). The idea of this experiment was to fabricate a gain medium (monovalent molecu- lar oxygen doped into single-crystal potassium chloride) for which the dipole dephasing rate could be controlled by varying the temperature of the sample. We found that at low tem- peratures the emission occurred through the process of superfluorescence, that is, the emis- sion took place in the form of a well-defined pulse occurring after a short time delay. At higher temperatures, the emission occurred as a result of ASE, and the emission was in the form of a longer, noisy pulse with no time delay. The experiment also showed how the nature of the emission changed as the dephasing rate was varied continuously between the two limiting values. These results led to some excitement in the theoretical community as attempts were made to model the experimental results [27, 28]. We have also performed fundamental studies in the field of nonlinear optics, includ- ing an investigation by Gauthier, Jerzy Krasinski, and myself of the role of atomic Rydberg states in leading to resonantly enhanced generation [29]. Malcuit and Gauthier worked with me on studies of how various nonlinear optical processes can compete with one another, at times in enormously subtle ways, such as the nearly complete suppression of one nonlinear optical process by another [30]. Martti Kauranen, William Davis, Elna Nagasako, and Gaeta worked on various aspects of how quantum noise can modify the behavior of various nonlinear optical processes [31]. Mark Gruneisen, Kenneth MacDonald, Gaeta and I worked on the construction of optical amplifiers based on four-photon nonlinear optical coupling [32, 33]. Robert Bridges worked on the influence of space-time coupling on the mode-locking of laser systems [34]. More recently we have has been actively engaged in studies of electromagnetically induced transparency (EIT) in various atomic systems. For example, Bennink, Vincent Wong, Carlos Stroud and I have studied EIT in two-level atomic systems [35]. In addition, Marlan Scully and I have investigated the use of quantum effects to increase the sensitivity of infrared detection [36], and Q-Han Park and I have shown how to control fundamental quan- tum optical processes through use of phase-coherent media [37]. Moreover, Girish Agarwal, Elna Nagasako, Sean Bentley and I have demonstrated theoretically the possibility of per- forming “quantum lithography” using light produced by a high-gain parametric amplifier [38].

Optical Phase Conjugation, Stimulated Light Scattering, and Fiber Nonlinear Optics

In the area of optical phase conjugation, we have performed theoretical studies of the role of quantum noise in phase conjugation [39], of the properties of the phase AJC-07.qxd 21/06/04 11:22 AM Page 298

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conjugation process [40, 41], of the process of Brillouin-enhanced four-wave mixing [42], of phase conjugate interferometry [43], and of techniques for single-pass aberration cor- rection [44]. Edward Miller performed experimental studies of ultrafast stimulated light scattering [45]. Thomas Moore performed detailed studies of the energetics of the process of stimulated Brillouin scattering [46] and observed chaos in the Brillouin interaction [47]. Mark Bowers and co-workers [48] designed and constructed phase conjugate laser systems based on stimulated Brillouin scattering. We have also been very interested in the nonlinear optical properties of optical fibers. Gaeta studied the nonlinear dynamics of the process of stimulated Brillouin scattering in optical fibers [49]. Andrew Stentz studied soliton formation in optical fibers [50]. Eric Buckland studied the various mechanisms of nonlinearity in optical fibers and concluded that in many circumstances electrostriction can make up to a 20 percent contribution [51, 52]. The present essay has summarized the history of the field of nonlinear optics from the perspective of The Institute of Optics. A historical account from a broader perspective has been presented by Bloembergen [53]. The field of nonlinear optics remains an extremely exciting field of scientific investigation. The Institute of Optics has played a key role in the history of the development of this field.

References

1. P. A. Franken, A. E. Hill, C. W. Peters, and G. Weinreich, Phys. Rev. Lett. 7, 118 (1961). 2. G. N. Lewis, D. Lipkin, and T. T. Magel, J. Am. Chem. Soc. 63, 3005 (1941). 3. M. A. Kramer, W. R. Tompkin, and R. W. Boyd, “Nonlinear Optical Interactions in Fluorescein-Doped Boric Acid Glass,” Phys. Rev. A 34, 2026 (1986). 4. G. N. Lewis, Nature 118, part 2, 874–75 (1926). 5. M. Hercher, J. Opt. Soc. Am. 54, 563 (1964). 6. J. H. Eberly, Phys. Rev. Lett. 15, 91 (1965). 7. H. B. Bebb and A. Gold, Phys. Rev. 143, 1 (1966). 8. D. J. Harter, P. Narum, M. G. Raymer, and R. W. Boyd, “Four-Wave Parametric Amplification of Rabi Sidebands in Sodium,” Phys. Rev. Lett. 46, 1192 (1981). 9. R. W. Boyd, M. G. Raymer, P. Narum, and D. J. Harter, “Four-Wave Parametric Interactions in a Strongly Driven Two-Level System,” Phys. Rev. A 24, 411 (1981). 10. I. A. Walmsley and M. G. Raymer, “Observation of Macroscopic Quantum Fluctuations in Stimulated Raman Scattering,” Phys. Rev. Lett. 50, 962–65 (1983). 11. R. W. Boyd, K. Rzazewski, and P. Narum, “Noise Initiation of Stimulated Brillouin Scattering,” Phys. Rev. A 42, 5514 (1990). 12. D. G. Hall and T. G. Dziura, “Transverse Effects in the Bistable Operation of Lasers Containing Saturable Absorbers,” Opt. Commun. 49, 146 (1984). 13. R. W. Boyd, Nonlinear Optics (Boston: Academic Press, 1992). 14. J. J. Maki, M. S. Malcuit, J. E. Sipe, and R. W. Boyd, “Linear and Nonlinear Optical Measurements of the Lorentz Local Field,” Phys. Rev. Lett. 68, 972 (1991). 15. J. E. Sipe and R. W. Boyd, “Nonlinear Susceptibility of Composite Optical Materials in the Maxwell Garnett Model,” Phys. Rev. A 46, 1614 (1992). 16. G. L. Fischer, R. W. Boyd, R. J. Gehr, S. A. Jenekhe, J. A. Osaheni, J. E. Sipe, and L. A. Weller-Brophy, “Enhanced Nonlinear Optical Response of Composite Materials,” Phys. Rev. Lett. 74, 1871 (1995). 17. R. L. Nelson and R. W. Boyd, “Enhanced Electrooptic Response of Layered Composite Materials,” Appl. Phys. Lett. 74, 2417 (1999). AJC-07.qxd 21/06/04 11:22 AM Page 299

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18. R. S. Bennink, Y.-K. Yoon, R. W. Boyd, and J. E. Sipe, “Accessing the Optical Nonlinearity of Metals with Metal-Dielectric Photonic Bandgap Structures,” Opt. Lett. 24, 1416 (1999). 19. J. E. Heebner and R. W. Boyd, “Enhanced All-Optical Switching by Use of a Nonlinear Fiber Ring Resonator,” Opt. Lett. 24, 847 (1999). 20. J. E. Heebner, R. W. Boyd, and Q.-H. Park, “Slow Light, Induced , Enhanced Nonlinearity, and Optical in a Nanostructured Waveguide, Phys. Rev. E 65, 036619 (2002). 21. R. W. Boyd, M. G. Raymer, and L. M. Narducci, eds., Optical Instabilities (Cambridge: Cambridge University Press, 1986). 22. D. J. Gauthier, P. Narum, and R. W. Boyd, “Observation of Deterministic Chaos in a Self- Pumped Phase Conjugate Mirror,” Phys. Rev. Lett. 58, 16 (1987). 23. A. L. Gaeta, R. W. Boyd, J. R. Ackerhalt, and P. W. Milonni, “Instabilities and Chaos in the Polarizations of Counterpropagating Light Fields,” Phys. Rev. Lett. 58, 2432 (1987). 24. D. J. Gauthier, M. S. Malcuit, and R. W. Boyd, “Polarization Instabilities of Counterpropagating Laser Beams in Sodium Vapor,” Phys. Rev. Lett. 61, 1827 (1988). 25. R. S. Bennink, V. Wong, A. M. Marino, D. L. Aronstein, R. W. Boyd, C. R. Stroud, Jr., S. Lukishova, and D. J. Gauthier, “Honeycomb Pattern Formation by Laser-Beam Filamentation in Atomic Sodium Vapor,” Phys. Rev. Lett. 88, 113901 (2002). 26. M. S. Malcuit, J. J. Maki, D. J. Simkin, and R. W. Boyd, “The Transition from Superfluorescence to Amplified Spontaneous Emission,” Phys. Rev. Lett. 59, 1189 (1987). 27. J. J. Maki, M. S. Malcuit, M. G. Raymer, R. W. Boyd, and P. D. Drummond, “Influence of Collisional Dephasing Processes on Superfluorescence,” Phys. Rev. A 40, 5135 (1989). 28. K. Rzazewski, M. G. Raymer, and R. W. Boyd, “Delay Time Statistics of Cooperative Emission in the Presence of Homogeneous Line Broadening,” Phys. Rev. A 39, 5785 (1989). 29. D. J. Gauthier, J. Krasinski, and R. W. Boyd, “Observation of Resonantly Enhanced Sum- Generation Involving Sodium Rydberg States,” Optics Letters 8, 211 (1983). 30. M. S. Malcuit, D. J. Gauthier, and R. W. Boyd, “Suppression of Amplified Spontaneous Emission by the Four-Wave Mixing Process,” Phys. Rev. Lett. 55, 1086 (1985). 31. W. V. Davis, M. Kauranen, E. Nagasako, R. J. Gehr, A. L. Gaeta, R. W. Boyd, and G. S. Agarwal, “Excess Noise Acquired by a Laser Beam in Propagating through an Atomic Potassium Vapor,” Phys. Rev. A 51, 4152 (1995). 32. M. T. Gruneisen, K. R. MacDonald, and R. W. Boyd, “Induced Gain and Modified Absorption of a Weak Probe Beam in a Strongly Driven Sodium Vapor,” J. Opt. Soc. Am. B 5, 123 (1988). 33. M. T. Gruneisen, K. R. MacDonald, A. L. Gaeta, and R. W. Boyd, “Laser Beam Combining in Potassium Vapor,” J. Quantum Electron 27, 198 (1991). 34. R. E. Bridges, R. W. Boyd, and G. P. Agrawal, “Effect of Beam Ellipticity on Self- Modelocking in Lasers,” Opt. Lett. 18, 2026 (1993). 35. R. S. Bennink, R. W. Boyd, C. R. Stroud, Jr., and V. Wong, “Enhanced Self-Action Effects by Electromagnetically Induced Transparency in The Two-Level Atom,” Phys. Rev. A 63, 033804 (2001). 36. R. W. Boyd and M. O. Scully, “Efficient Infrared Imaging Upconversion via Quantum Coherence,” Appl. Phys. Lett. 77, 3559 (2000). 37. Q. H. Park and R. W. Boyd, “Modification of Self-Induced Transparency by a Coherent Control Field,” Phys. Rev. Lett. 86, 2774 (2001). 38. G. S. Agarwal, R. W. Boyd, E. M. Nagasako, and S. J. Bentley, “Comment on ‘Quantum Interferometric Optical Lithography: Exploiting Entanglement to Beat the Diffraction Limit,’ ” Phys. Rev. Lett. 86, 1389 (2001). 39. A. L. Gaeta and R. W. Boyd, “Quantum Noise in Phase Conjugation,” Phys. Rev. Lett. 60, 2618 (1988). AJC-07.qxd 21/06/04 11:22 AM Page 300

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40. M. S. Malcuit, D. J. Gauthier, and R. W. Boyd, “Vector Phase Conjugation by Two-Photon Resonant Degenerate Four-Wave Mixing,” Opt. Lett. 13, 663 (1988). 41. M. Kauranen, D. J. Gauthier, M. S. Malcuit, and R. W. Boyd, “Polarization Properties of Phase Conjugation by Two-Photon Resonant Degenerate Four-Wave Mixing,” Phys. Rev. A 40, 1908 (1989). 42. M. D. Skeldon, P. Narum, and R. W. Boyd, “Non-Frequency Shifted, High-Quality Phase Conjugation with Aberrated Pump Waves by Brillouin-Enhanced Four-Wave Mixing,” Opt. Lett. 12, 343 (1987). 43. D. J. Gauthier, R. W. Boyd, R. K. Jungquist, J. B. Lisson, and L. L. Voci, “Phase- Conjugate Fizeau Interferometer,” Opt. Lett. 14, 325 (1989). 44. K. R. MacDonald, W. R. Tompkin, and R. W. Boyd, “Passive One-Way Aberration Correction Using Four-wave Mixing,” Opt. Lett. 13, 663 (1988). 45. E. J. Miller, M. S. Malcuit, and R. W. Boyd, “Simultaneous Wavefront and Polarization Conjugation of Picosecond Optical Pulses by Stimulated Rayleigh-Wing Scattering,” Optics Letters 15, 1188 (1990). 46. O. Kulagin, G. A. Pasmanik, A. L. Gaeta, T. R. Moore, G. J. Benecke, and R. W. Boyd, “Observation of Brillouin Chaos with Counterpropagating Laser Beams,” J. Opt. Soc. B 8, 2155 (1991). 47. T. R. Moore, G. L. Fischer, and R. W. Boyd, “Measurement of the Power Distribution During Stimulated Brillouin Scattering with Focused Gaussian Beams,” Journal of Modern Optics 45, 735–45 (1998). 48. M. W. Bowers, R. W. Boyd, and A. K. Hankla, “Brillouin-Enhanced Four-Wave-Mixing Vector Phase Conjugate Mirror with Beam Combining Capability,” Opt. Lett. 22, 360–62 (1999). 49. A. L. Gaeta and R. W. Boyd, “Stochastic Dynamics of Stimulated Brillouin Scattering in an Optical Fiber,” Phys. Rev. A 44, 3205 (1991). 50. A. J. Stentz, R. W. Boyd, and A. F. Evans, “Dramatically Improved Transmission of Ultrashort Solitons through 40 km of Dispersion-Decreasing Fiber,” Opt. Lett. 20, 1770 (1995). 51. E. L. Buckland and R. W. Boyd, “Measurement of the Frequency Response of the Electrostrictive Nonlinearity in Optical Fibers,” Optics Letters 22, 676 (1997). 52. E. L. Buckland and R. W. Boyd, “Electrostrictive Contribution to the Intensity-Dependent of Optical Fibers,” Opt. Lett. 21, 1117–19 (1996). 53. N. Bloembergen, IEEE Selected Topics in Quantum Electronics 6, 876 (2000).

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