Optical vortices, which carry orbital angular momentum (OAM), can be flexibly produced and measur... more Optical vortices, which carry orbital angular momentum (OAM), can be flexibly produced and measured with infrared and visible light. Their application is an important research topic for super-resolution imaging, optical communications and quantum optics. However, only a few methods can produce OAM beams in the extreme ultraviolet (XUV) or X-ray, and controlling the OAM on these beams remains challenging. Here we apply wave mixing to a tabletop high-harmonic source, as proposed in our previous work, and control the topological charge (OAM value) of XUV beams. Our technique enables us to produce first-order OAM beams with the smallest possible central intensity null at XUV wavelengths. This work opens a route for carrier-injected laser machining and lithography, which may reach nanometre or even angstrom resolution. Such a light source is also ideal for space communications, both in the classical and quantum regimes.
Stable spatial laser patterns were observed in a high-finesse Fabry-Perot cavity containing up to... more Stable spatial laser patterns were observed in a high-finesse Fabry-Perot cavity containing up to 2 atm of CO 2 and O 2. The gases displayed the same sequence of patterns that obey a scaling law of the form P b p 2 , where P is the power stored in the cavity, p is the pressure of the gas, and b is a material-dependent parameter.
Proceedings of the National Academy of Sciences, 2014
Significance In 2012, Menzel et al. reported on the results of a fundamental experiment raising q... more Significance In 2012, Menzel et al. reported on the results of a fundamental experiment raising questions regarding the simultaneous observation of wave-like and particle-like properties in a given quantum system. Whereas the general applicability of the duality principle to entangled subsystems is an open question, we bring the current understanding of the duality principle a step forward by theoretically deriving the strongest relations between the visibility of an interference pattern and the which-way information in a two-way interferometer such as Young’s double slit. This formalism successfully describes tests of duality where postselection on a subset of the interference pattern is applied. Our analysis even reconciles the surprising results of Menzel et al. with the duality principle in its standard form.
We present a novel method for efficient sorting of photons prepared in states of orbital angular ... more We present a novel method for efficient sorting of photons prepared in states of orbital angular momentum (OAM) and angular position (ANG). A log-polar optical transform is used in combination with a holographic beam-splitting method to achieve better mode discrimination and reduced cross-talk than reported previously. Simulating this method for 7 modes, we have calculated an improved mutual information of 2.43 bits/photon and 2.29 bits/photon for OAM and ANG modes respectively. In addition, we present preliminary results from an experimental implementation of this technique. This method is expected to have important applications for high-dimensional quantum key distribution systems.
We demonstrate a simple experimental method for creating entangled qudits. Using transversemoment... more We demonstrate a simple experimental method for creating entangled qudits. Using transversemomentum and position entanglement of photons emitted in spontaneous parametric down-conversion, we show entanglement between discrete regions of space, i.e., pixels. We map each photon onto as many as six pixels, where each pixel represents one level of our qudit state. The method is easily generalizable to create even higher dimensional, entangled states. Thus, the realization of quantum information processing in arbitrarily high dimensions is possible, allowing for greatly increased information capacity.
We have observed transverse pattern formation leading to highly regular structures in both the ne... more We have observed transverse pattern formation leading to highly regular structures in both the near and far fields when a near-resonant laser beam propagates without feedback through an atomic sodium vapor. One example is a regular far-field honeycomb pattern, which results from the transformation of the laser beam within the vapor into a stable three-lobed structure with a uniform phase distribution and highly correlated power fluctuations. The predictions of a theoretical model of the filamentation process are in good agreement with these observations.
The nonlinear optical response of porous InP͑100͒ membranes was examined and compared to that of ... more The nonlinear optical response of porous InP͑100͒ membranes was examined and compared to that of bulk crystalline ͑100͒-oriented InP. Measurements of optical rectification and optical second-harmonic generation have been carried out in reflection under excitation by 120 fs, 800 nm Ti:Sapphire laser beam pulses. A significant enhancement in both the radiated terahertz field and second-harmonic radiation from the porous InP͑100͒ surface, relative to the bulk InP͑100͒ surface, was observed. Terahertz field polarization measurements indicate that the enhancement is primarily on the component of the radiated field related to optical rectification as opposed to photocarrier-related effects. It is suggested that the enhanced nonlinear optical response is related to strong enhancements of the local field within the porous network.
Contributions to the fifth-order nonlinear optical susceptibility ͑5͒ of a collection of homogene... more Contributions to the fifth-order nonlinear optical susceptibility ͑5͒ of a collection of homogeneously broadened two-level atoms that scale as N 2 ͑␥ at ͑3͒ ͒ 2 and N 2 ͉␥ at ͑3͒ ͉ 2 , where ␥ at ͑3͒ is the lower-order atomic hyperpolarizability and N is the atomic number density, are predicted theoretically. These "cascaded" contributions are a consequence of local-field effects. We determine them from a fifth-order solution of the Lorentz-Maxwell-Bloch equations. They are missing from a straightforward generalization of Bloembergen's result for the local field correction to the second order nonlinearity, but are recovered by a careful application of his general approach. We find that at high atomic densities ͑N Ͼ 10 15 cm −3 ͒ the value of the cascaded third-order contribution can be as large as the "direct" fifth-order term in the expression for the fifth-order susceptibility.
We investigate the effect of turbulence on quantum ghost imaging. We use entangled photons and de... more We investigate the effect of turbulence on quantum ghost imaging. We use entangled photons and demonstrate that for a novel experimental configuration the effect of turbulence can be greatly diminished. By decoupling the entangled photon source from the ghost imaging central image plane, we are able to dramatically increase the ghost image quality. When imaging a test pattern through turbulence, this method increased the imaged pattern visibility from V = 0.15 ± 0.04 to V = 0.42 ± 0.04.
The thermal contribution to the nonlinear refractive index of air at 1.064 mm was measured with a... more The thermal contribution to the nonlinear refractive index of air at 1.064 mm was measured with a highfinesse Fabry-Perot cavity and a 500-mW cw laser beam. At room temperature and pressure, the nonlinear refractive-index coefficient of air was found to be n 2 ͑th͒ ͑21.9 6 0.2͒ 3 10 214 cm 2 ͞W for a beam waist radius of 0.23 mm and was found to be independent of the relative humidity. The thermal nonlinearities of N 2 , O 2 , and CO 2 were also measured, and it was found that the dominant contribution to air is its O 2 content.
Metals typically have very large nonlinear susceptibilities (ϳ10 6 times larger than those of typ... more Metals typically have very large nonlinear susceptibilities (ϳ10 6 times larger than those of typical dielectrics), but because they are nearly opaque their nonlinear properties are effectively inaccessible. We demonstrate numerically that a multilayer metal-dielectric structure in which the metal is the dominant nonlinear ͓x ͑3͒ ͔ material can have much larger intensity-dependent changes in the complex amplitude of the transmitted beam than a bulk sample containing the same thickness of metal. For 80 nm of copper the magnitude of the nonlinear phase shift is predicted to be as much as 40 times larger for the layered copper-silica sample, and the transmission is also greatly increased. The effective nonlinear refractive-index coeff icient n 2 of this composite material can be as large as ͑3 1 6i͒ 3 10 29 cm 2 ͞W, which is among the largest values for known, reasonably transmissive materials.
We have constructed and characterized several optical microring resonators with scale sizes of th... more We have constructed and characterized several optical microring resonators with scale sizes of the order of 10 mm. These devices are intended to serve as building blocks for engineerable linear and nonlinear photonic media. Light is guided vertically by an epitaxially grown structure and transversely by deeply etched air-clad sidewalls. We report on the spectral phase transfer characteristics of such resonators. We also report the observation of a p-rad Kerr nonlinear phase shift accumulated in a single compact ring resonator evidenced by all-optical switching between output ports of a resonator-enhanced Mach-Zehnder interferometer.
We describe a compact, tunable, optical time-delay module that functions by means of total intern... more We describe a compact, tunable, optical time-delay module that functions by means of total internal reflection within two glass prisms. The delay is controlled by small mechanical motions of the prisms. The device is inherently extremely broad band, unlike time delay modules based on "slow light" methods. In the prototype device that we fabricated, we obtain time delays as large as 1.45 ns in a device of linear dimensions of the order of 3.6 cm. We have delayed pulses with a full width at half-maximum pulse duration of 25 fs, implying a delay bandwidth product (measured in delay time divided by the FWHM pulse width) of 5.8x10 4. We also show that the dispersion properties of this device are sufficiently small that quantum features of a light pulse are preserved upon delay.
Optical vortices, which carry orbital angular momentum (OAM), can be flexibly produced and measur... more Optical vortices, which carry orbital angular momentum (OAM), can be flexibly produced and measured with infrared and visible light. Their application is an important research topic for super-resolution imaging, optical communications and quantum optics. However, only a few methods can produce OAM beams in the extreme ultraviolet (XUV) or X-ray, and controlling the OAM on these beams remains challenging. Here we apply wave mixing to a tabletop high-harmonic source, as proposed in our previous work, and control the topological charge (OAM value) of XUV beams. Our technique enables us to produce first-order OAM beams with the smallest possible central intensity null at XUV wavelengths. This work opens a route for carrier-injected laser machining and lithography, which may reach nanometre or even angstrom resolution. Such a light source is also ideal for space communications, both in the classical and quantum regimes.
Stable spatial laser patterns were observed in a high-finesse Fabry-Perot cavity containing up to... more Stable spatial laser patterns were observed in a high-finesse Fabry-Perot cavity containing up to 2 atm of CO 2 and O 2. The gases displayed the same sequence of patterns that obey a scaling law of the form P b p 2 , where P is the power stored in the cavity, p is the pressure of the gas, and b is a material-dependent parameter.
Proceedings of the National Academy of Sciences, 2014
Significance In 2012, Menzel et al. reported on the results of a fundamental experiment raising q... more Significance In 2012, Menzel et al. reported on the results of a fundamental experiment raising questions regarding the simultaneous observation of wave-like and particle-like properties in a given quantum system. Whereas the general applicability of the duality principle to entangled subsystems is an open question, we bring the current understanding of the duality principle a step forward by theoretically deriving the strongest relations between the visibility of an interference pattern and the which-way information in a two-way interferometer such as Young’s double slit. This formalism successfully describes tests of duality where postselection on a subset of the interference pattern is applied. Our analysis even reconciles the surprising results of Menzel et al. with the duality principle in its standard form.
We present a novel method for efficient sorting of photons prepared in states of orbital angular ... more We present a novel method for efficient sorting of photons prepared in states of orbital angular momentum (OAM) and angular position (ANG). A log-polar optical transform is used in combination with a holographic beam-splitting method to achieve better mode discrimination and reduced cross-talk than reported previously. Simulating this method for 7 modes, we have calculated an improved mutual information of 2.43 bits/photon and 2.29 bits/photon for OAM and ANG modes respectively. In addition, we present preliminary results from an experimental implementation of this technique. This method is expected to have important applications for high-dimensional quantum key distribution systems.
We demonstrate a simple experimental method for creating entangled qudits. Using transversemoment... more We demonstrate a simple experimental method for creating entangled qudits. Using transversemomentum and position entanglement of photons emitted in spontaneous parametric down-conversion, we show entanglement between discrete regions of space, i.e., pixels. We map each photon onto as many as six pixels, where each pixel represents one level of our qudit state. The method is easily generalizable to create even higher dimensional, entangled states. Thus, the realization of quantum information processing in arbitrarily high dimensions is possible, allowing for greatly increased information capacity.
We have observed transverse pattern formation leading to highly regular structures in both the ne... more We have observed transverse pattern formation leading to highly regular structures in both the near and far fields when a near-resonant laser beam propagates without feedback through an atomic sodium vapor. One example is a regular far-field honeycomb pattern, which results from the transformation of the laser beam within the vapor into a stable three-lobed structure with a uniform phase distribution and highly correlated power fluctuations. The predictions of a theoretical model of the filamentation process are in good agreement with these observations.
The nonlinear optical response of porous InP͑100͒ membranes was examined and compared to that of ... more The nonlinear optical response of porous InP͑100͒ membranes was examined and compared to that of bulk crystalline ͑100͒-oriented InP. Measurements of optical rectification and optical second-harmonic generation have been carried out in reflection under excitation by 120 fs, 800 nm Ti:Sapphire laser beam pulses. A significant enhancement in both the radiated terahertz field and second-harmonic radiation from the porous InP͑100͒ surface, relative to the bulk InP͑100͒ surface, was observed. Terahertz field polarization measurements indicate that the enhancement is primarily on the component of the radiated field related to optical rectification as opposed to photocarrier-related effects. It is suggested that the enhanced nonlinear optical response is related to strong enhancements of the local field within the porous network.
Contributions to the fifth-order nonlinear optical susceptibility ͑5͒ of a collection of homogene... more Contributions to the fifth-order nonlinear optical susceptibility ͑5͒ of a collection of homogeneously broadened two-level atoms that scale as N 2 ͑␥ at ͑3͒ ͒ 2 and N 2 ͉␥ at ͑3͒ ͉ 2 , where ␥ at ͑3͒ is the lower-order atomic hyperpolarizability and N is the atomic number density, are predicted theoretically. These "cascaded" contributions are a consequence of local-field effects. We determine them from a fifth-order solution of the Lorentz-Maxwell-Bloch equations. They are missing from a straightforward generalization of Bloembergen's result for the local field correction to the second order nonlinearity, but are recovered by a careful application of his general approach. We find that at high atomic densities ͑N Ͼ 10 15 cm −3 ͒ the value of the cascaded third-order contribution can be as large as the "direct" fifth-order term in the expression for the fifth-order susceptibility.
We investigate the effect of turbulence on quantum ghost imaging. We use entangled photons and de... more We investigate the effect of turbulence on quantum ghost imaging. We use entangled photons and demonstrate that for a novel experimental configuration the effect of turbulence can be greatly diminished. By decoupling the entangled photon source from the ghost imaging central image plane, we are able to dramatically increase the ghost image quality. When imaging a test pattern through turbulence, this method increased the imaged pattern visibility from V = 0.15 ± 0.04 to V = 0.42 ± 0.04.
The thermal contribution to the nonlinear refractive index of air at 1.064 mm was measured with a... more The thermal contribution to the nonlinear refractive index of air at 1.064 mm was measured with a highfinesse Fabry-Perot cavity and a 500-mW cw laser beam. At room temperature and pressure, the nonlinear refractive-index coefficient of air was found to be n 2 ͑th͒ ͑21.9 6 0.2͒ 3 10 214 cm 2 ͞W for a beam waist radius of 0.23 mm and was found to be independent of the relative humidity. The thermal nonlinearities of N 2 , O 2 , and CO 2 were also measured, and it was found that the dominant contribution to air is its O 2 content.
Metals typically have very large nonlinear susceptibilities (ϳ10 6 times larger than those of typ... more Metals typically have very large nonlinear susceptibilities (ϳ10 6 times larger than those of typical dielectrics), but because they are nearly opaque their nonlinear properties are effectively inaccessible. We demonstrate numerically that a multilayer metal-dielectric structure in which the metal is the dominant nonlinear ͓x ͑3͒ ͔ material can have much larger intensity-dependent changes in the complex amplitude of the transmitted beam than a bulk sample containing the same thickness of metal. For 80 nm of copper the magnitude of the nonlinear phase shift is predicted to be as much as 40 times larger for the layered copper-silica sample, and the transmission is also greatly increased. The effective nonlinear refractive-index coeff icient n 2 of this composite material can be as large as ͑3 1 6i͒ 3 10 29 cm 2 ͞W, which is among the largest values for known, reasonably transmissive materials.
We have constructed and characterized several optical microring resonators with scale sizes of th... more We have constructed and characterized several optical microring resonators with scale sizes of the order of 10 mm. These devices are intended to serve as building blocks for engineerable linear and nonlinear photonic media. Light is guided vertically by an epitaxially grown structure and transversely by deeply etched air-clad sidewalls. We report on the spectral phase transfer characteristics of such resonators. We also report the observation of a p-rad Kerr nonlinear phase shift accumulated in a single compact ring resonator evidenced by all-optical switching between output ports of a resonator-enhanced Mach-Zehnder interferometer.
We describe a compact, tunable, optical time-delay module that functions by means of total intern... more We describe a compact, tunable, optical time-delay module that functions by means of total internal reflection within two glass prisms. The delay is controlled by small mechanical motions of the prisms. The device is inherently extremely broad band, unlike time delay modules based on "slow light" methods. In the prototype device that we fabricated, we obtain time delays as large as 1.45 ns in a device of linear dimensions of the order of 3.6 cm. We have delayed pulses with a full width at half-maximum pulse duration of 25 fs, implying a delay bandwidth product (measured in delay time divided by the FWHM pulse width) of 5.8x10 4. We also show that the dispersion properties of this device are sufficiently small that quantum features of a light pulse are preserved upon delay.
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Papers by Robert Boyd