Coherent Light Field Research Articles

Optical detection of motion generated in soft tissue by a focused ultrasound beam.

This presentation will discuss various approaches combining light and sound for tissue characterization. All the approaches discussed here involve the optical detection of motion generated at depth in tissue by use of a focused ultrasound transducer. In the first part of the presentation, the acousto-optic imaging approach will be described, in which the optical phase modulation created by an ultrasound beam is used to derive optical properties with the resolution of the ultrasound beam. In particular, it will be demonstrated that randomly phase-modulated millisecond ultrasound burst can be used to obtain both transverse and axial resolutions. In this first approach, the optically detected motion consists of the ultrasonic motion of insonified light scatterers. In the second part of the presentation, it will be demonstrated that it is also possible to optically detect the transient shear motion generated by the acoustic radiation force in soft tissue. As for acousto-optic imaging, this approach is based on the interaction between a diffuse coherent light field and a localized motion and therefore provides localized information in the sample. In addition to provide information on optical properties, this approach also provides information on shear stiffness on the medium. For both approaches, experimental results obtained in vitro on tissue or tissue-mimicking phantoms will be shown, and the current challenges toward in vivo measurements will be discussed.

Phase shaping of single-photon wave packets

Although the phase of a coherent light field can be precisely known, this is not true for the phase of the individual photons that create the field, considered individually1. Phase changes within single-photon wave packets, however, have observable effects. In fact, actively controlling the phase of individual photons has been identified as a powerful resource for quantum communication protocols2,3. Here we demonstrate arbitrary phase control of a single photon. The phase modulation is applied without affecting the photon's amplitude profile and is verified by means of a two-photon quantum interference measurement4,5, demonstrating fermionic spatial behaviour of photon pairs. Combined with previously demonstrated control of a single photon's amplitude6,7,8,9,10, frequency11, and polarization12, the fully deterministic phase shaping presented here allows for the complete control of single-photon wave packets. Arbitrary phase control within a single photon wave packet is demonstrated and verified by two-photon quantum interference measurements. Combined with the previously demonstrated ability to control a single photon's amplitude, frequency and polarization, the phase shaping presented here allows for the complete control of single-photon wave packets.

Three-dimensional holographic imaging of living tissue using a highly sensitive photorefractive polymer device

Photorefractive materials are dynamic holographic storage media that are highly sensitive to coherent light fields and relatively insensitive to a uniform light background. This can be exploited to effectively separate ballistic light from multiply-scattered light when imaging through turbid media. We developed a highly sensitive photorefractive polymer composite and incorporated it into a holographic optical coherence imaging system. This approach combines the advantages of coherence-domain imaging with the benefits of holography to form a high-speed wide-field imaging technique. By using coherence-gated holography, image-bearing ballistic light can be captured in real-time without computed tomography. We analyzed the implications of Fourier-domain and image-domain holography on the field of view and image resolution for a transmission recording geometry, and demonstrate holographic depth-resolved imaging of tumor spheroids with 12 microm axial and 10 microm lateral resolution, achieving a data acquisition speed of 8 x 10(5) voxels/s.

Realization of a Multiqubit Conditional Phase Gate by Virtue of a Weak Coherent Light Field

We propose a scalable scheme to generate a multiqubit conditional phase gate by using a basic building block, i.e., a weak coherent optical pulse |α〉 reflected successively from a cavity with trapped atoms. In the scheme, we use a coherent state of light instead of a single photon source, homodyne measurement on a coherent light field instead of single photon detection, which reduces the complexity of the practical experiment. The outcomes of these measurements indicate either completion of the gate or the presence of the original qubits such that the operation can be repeated until it is successful.

Observation of bipartite correlations using coherent light for optical communication

Bipartite polarization correlations of two distant observers are observed by using coherent noise interferences. This is accomplished by mixing a vertically polarized coherent light field with a horizontally polarized coherent noise field in a 50/50 beam splitter. The superposed light fields at each output port of the beam splitter are sent to two observers and then manipulated by using a quarter-wave plate and an analyzer. The bipartite correlations between the projection angles of two distant observers are established by analyzing their data through multiplication without any postselection technique. The scheme can be used to implement entanglement-based quantum cryptography in the future.

Quantum properties of the entangled coherent light field under the anti-Jaynes-Cummings model

A two-level atom drvien by a strong classical field interacts with a single-mode light field, and the interaction between the atom and the light field can turn into an effective anti-Jaynes-Cummings model under the conditions of strong driving and large detuning. In this paper, we mainly study the two-mode entangled coherent light field in this model, in which one mode of the entangled coherent light field interacts with a two-level atom driven by a strong classical field. During the evolution of the total system, we make a selective measurement on the atom. Through tuning the evolution time and the parameter of the coherent field, we can easily control the quantum statistical properties of the other mode of the entangled light fields and generate the expected non-classical light field in a longer interaction time and a wider region of coherent parameter.

Generation of Four-Photon Cluster State with Coherent Light via Cross-Kerr Nonlinearity

We propose two schemes for preparing four-photon cluster state through cross-Kerr nonlinearity. Two coherent fields interact when they enter a nonlinear Kerr medium. If the interaction time is chosen appropriately in each Kerr medium, four-photon cluster state can be generated based on the results of two homodyne detectors in the first scheme. These schemes only use Kerr medium and homodyne measurements on coherent light fields, which can be efficiently made in quantum optical laboratories. In addition, weak cross-Kerr nonlinearity is sufficient. All of the properties make these schemes feasible in experiments.

Evolution of the field quantum entropy and entanglement in a system of multimode light field interacting resonantly with a two-level atom through N j -degenerate N Σ-photon process

The time evolution of the field quantum entropy and entanglement in a system of multi-mode coherent light field resonantly interacting with a two-level atom by degenerating the multi-photon process is studied by utilizing the Von Neumann reduced entropy theory, and the analytical expressions of the quantum entropy of the multimode field and the numerical calculation results for three-mode field interacting with the atom are obtained. Our attention focuses on the discussion of the influences of the initial average photon number, the atomic distribution angle and the phase angle of the atom dipole on the evolution of the quantum field entropy and entanglement. The results obtained from the numerical calculation indicate that: the stronger the quantum field is, the weaker the entanglement between the quantum field and the atom will be, and when the field is strong enough, the two subsystems may be in a disentangled state all the time; the quantum field entropy is strongly dependent on the atomic distribution angle, namely, the quantum field and the two-level atom are always in the entangled state, and are nearly stable at maximum entanglement after a short time of vibration; the larger the atomic distribution angle is, the shorter the time for the field quantum entropy to evolve its maximum value is; the phase angles of the atom dipole almost have no influences on the entanglement between the quantum field and the two-level atom. Entangled states or pure states based on these properties of the field quantum entropy can be prepared.

Calculation of Hyper-Geometric Modes ¶

We develop an algorithm for calculating hyper-geometric modes of the coherent light field, which represent a solution to the paraxial wave (Schrodinger-type) equation. The propagation of the hyper-geometric modes containing a phase spiral singularity is computer simulated. A comparison is conducted of the exact analytical solution and an approximate solution derived using an integral Kirchhoff propagation operator. A specific feature of the hyper-geometric modes that distinguish them from the familiar paraxial (Gauss, Bessel) modes is that the major radius of the former increases as a square root of the distance passed and the spacing between the adjacent maxima (or minima) in the diffraction pattern decreases with increasing radial coordinate.

Squeezing of an atom laser originating from atomic Bose–Einstein condensate interacting with light field

The quadrature squeezing properties of an atom laser originating from atomic Bose–Einstein condensate interacting with light field are studied. We find that the squeezing properties of the atom laser are dependent on the initial light field interacting with the atomic Bose–Einstein condensate. If the initial light field cannot be squeezed, such as number state or coherent state light field, the atom laser as well cannot be squeezed. However, if the initial light field interacting with the atomic Bose–Einstein condensate being in squeezed state, the atom laser can be squeezed periodically, and its squeezing depth is dependent on the intensity of interatoms interaction.

Scattering approach to semiconductor double quantum dot cavities

The interaction of a coherent light field with two adjacent two-sided cavities, each containing a semiconductor quantum dot which is charged by a single excess electron, is studied within $S$-matrix theory. Dissipation in the nonresonantly driven dots and intercavity losses are treated phenomenologically. Light transmission is studied as a function of the initial state of the quantum dots (QDs), light polarization, dissipative losses, as well as dissimilarities between the two QD cavities. The transmission spectrum consists of a superposition of resonances from the individual cavities and Fabry-P\'erot-like resonances associated with the double cavity. Faraday rotation and phase shifts caused by the nonresonantly driven trion transition allow nondestructive distinction between parallel ``up,'' ``down,'' and antiparallel spin orientation for the two excess electrons for identical cavities. With increasing asymmetry between the two cavities, the transmission spectrum reveals more and more the initial spin orientation of the individual electrons. Selection of the center frequency and duration of the incident laser pulse allows us to reveal preferentially either the relative spin orientation, needed as prerequisite for entanglement generation, or the orientation of individual spins. A quantitative estimate of the effects on the transmitted light arising from various physical sources of dissimilarities, as well as the effect from remote transitions, is given for typical system parameters.

Angular momentum exchange between coherent light and matter fields

Full, three-dimensional time-dependent simulations are presented demonstrating the quantized transfer of angular momentum to a Bose-Einstein condensate from a laser carrying orbital angular momentum in a Laguerre-Gaussian mode. The process is described in terms of coherent Bragg scattering of atoms from a chiral optical lattice. The transfer efficiency and the angular momentum content of the output coupled vortex state are analyzed and compared with a recent experiment.

Family of hypergeometric laser beams

We discuss a three-parameter family of paraxial coherent light fields that originate from a complex amplitude composed of the following four cofactors: the Gaussian beam, a logarithmic axicon, a spiral phase plate (angular harmonic), and an amplitude power function with a possible singularity at the origin of coordinates. For such types of beams, the near-field complex amplitude is proportional to the degenerate hypergeometric function, prompting the beams' name--hypergeometric (HyG) beams. When the Gaussian beam is replaced by a plane wave, the above beams change to generalized HyG modes that preserve their structure up to scale upon propagation. The intensity profile of the HyG beams is similar to that of the Bessel modes, forming a set of alternating bright and dark rings. However, the thickness of the rings of the HyG beams decreases with increasing ring number.

Measuring spatial coherence by using a mask with multiple apertures

A simple method to measure the complex degree of spatial coherence of a partially coherent quasi-monochromatic light field is presented. The Fourier spectrum of the far-field interferogram generated by a mask with multiple apertures (small circular holes) is analyzed in terms of classes of aperture pairs. A class of aperture pairs is defined as the set of aperture pairs with the same separation vector. The height of the peaks in the magnitude spectrum determines the modulus of the complex degree of spatial coherence and the corresponding value in the phase spectrum determines the phase of the complex degree of spatial coherence. The method is illustrated with experimental results.

Longitudinal purely spatial coherence of a light field

The effects of longitudinal purely spatial coherence of light and the results of observation of these effects in an interference experiment are considered under the condition that the length of temporal coherence l c is considerably smaller than the length of longitudinal spatial coherence ρ‖ of the field. It is shown that, for l c ≪ ρ‖, the longitudinal purely spatial coherence of the light field in fact governs the coherence of the wave train in the process of its propagation. The length and the time of coherent (“free”) path of the wave train are considered as new spatial and temporal scales of a partially coherent light field.

Measuring spatial coherence by using a reversed-wavefront Young interferometer

A very simple optical setup for the measurement of the modulus and the phase of the two-point correlation function of a partially coherent light field is presented. The system consists of a slightly modified version of a Young interferometer and requires a single Young mask in order to determine the correlation function at any pairs of points. Experimental results are presented for the case of a synthesized partially coherent secondary source.

The effect of phase modulation of scattered radiation on the asymptotic behavior of the contrast ratio of partially coherent speckle fields

We analyze the influence of a weak phase modulation of multiply scattered partially coherent light fields on the variance of fluctuations of the scattered field intensity. It is suggested to perform diagnostics of scattering media by analyzing the probing radiation scattered from a “modulating” medium and determining the speckle intensity index (or contrast ratio) upon introduction of an object studied into the scheme of measurements. The proposed method is experimentally verified on model scattering media.

Quantum trajectory approach to stochastically‐induced quantum interference

AbstractStochastic perturbation of two‐level atoms strongly driven by a coherent light field is analyzed by the quantum trajectory method. Narrow resonances as hole burning and dispersive Fano‐like profile occur in the spectra in the regime where the noise dominates the Rabi oscillations. It is shown that in this case the stochastic noise can unexpectedly create phase correlation between the neighboring atomic dressed states. This phase correlation is responsible for quantum interference between the related transitions resulting in anomalous modifications of the resonance fluorescence spectra.

Quantum-trajectory approach to stochastically induced quantum-interference effects in coherently driven two-level atoms

Stochastic perturbation of two-level atoms strongly driven by a coherent light field is analyzed by the quantum trajectory method. A new method is developed for calculating the resonance fluorescence spectra from numerical simulations. It is shown that in the case of dominant incoherent perturbation, the stochastic noise can unexpectedly create phase correlation between the neighboring atomic dressed states. This phase correlation is responsible for quantum interference between the related transitions resulting in anomalous modifications of the resonance fluorescence spectra.

Focal spots of size lambda/23 open up far-field fluorescence microscopy at 33 nm axial resolution.

We report spots of excited molecules of 33 nm width created with focused light of lambda = 760 nm wavelength and conventional optics along the optic axis. This is accomplished by exciting the molecules with a femtosecond pulse and subsequent depletion of their excited state with red-shifted, picosecond-pulsed, counterpropagating, coherent light fields. The lambda/23 ratio constitutes what is to our knowledge the sharpest spatial definition attained with freely propagating electromagnetic radiation. The sub-diffraction spots enable for the first time far-field fluorescence microscopy with resolution at the tens of nanometer scale, as demonstrated in images of membranes of bacillus megaterium.