Spatial Coherence Control Research Articles

Manipulating the Spatial Structure of Second-Order Quantum Coherence Using Entangled Photons

Abstract High-order quantum coherence reveals the statistical correlation of quantum particles. Manipulation of quantum coherence of light in the temporal domain enables the production of the single-photon source, which has become one of the most important quantum resources. High-order quantum coherence in the spatial domain plays a crucial role in a variety of applications, such as quantum imaging, holography, and microscopy. However, the active control of second-order spatial quantum coherence remains a challenging task. Here we predict theoretically and demonstrate experimentally the first active manipulation of second-order spatial quantum coherence, which exhibits the capability of switching between bunching and anti-bunching, by mapping the entanglement of spatially structured photons. We also show that signal processing based on quantum coherence exhibits robust resistance to intensity disturbance. Our findings not only enhance existing applications but also pave the way for broader utilization of higher-order spatial quantum coherence.

Spatial coherent control of quantum pathways with counter-propagating femtosecond pulse pairs

Quantum pathways 5S1/2−5P1/2−5D and 5S1/2−5P3/2−5D in atomic rubidium upon excitation are hard to identify spectrally due to the ultrafast and broadband nature of femtosecond pulses. By introducing additional spatial dimension, counter-propagating pulse pairs entangles the pathway information and the optical paths, and thus can resolve the two pathways in space. In this paper, the spatial coherent control method is employed to identify and manipulate quantum pathways. Square and linear phase-shaping schemes that combine amplitude shaping are proposed for a three-level model system, and the corresponding parameters are carefully fine-tuned to obtain a clear spatial two-photon transition pattern. Local maximums appear in the two-photon transition spatial profile with the square phase-shaping scheme, and the underlying physics is discussed. As well as themselves, the square and linear phase-shaping strategies can also be combined to give two hybrid schemes to well resolve the two pathways of atomic rubidium, and these four schemes can all be employed to manipulate quantum pathways for seeking redirection of all the dynamics to one specific pathway by additionally blocking the specific spectral bands with amplitude modulation.

Spatial coherence control and analysis via micromirror-based mixed-state ptychography

Flexible and fast control of the phase and amplitude of coherent light, enabled by digital micromirror devices (DMDs) and spatial light modulators, has been a driving force for recent advances in optical tweezers, nonlinear microscopy, and wavefront shaping. In contrast, engineering spatially partially coherent light remains widely elusive due to the lack of tools enabling a joint analysis and control sequence. Here, we report an approach to coherence engineering that combines a quasi-monochromatic, thermal source and a DMD together with a ptychographic scanning microscope. The reported method opens up new routes to low-cost coherence control, with applications in micromanipulation, nanophotonics, and quantitative phase contrast imaging.

Investigation of coherence properties of white light emission of tungsten lamp additionally excited with laser radiation

The coherence properties of white light emission of a tungsten incandescent lamp additionally excited with laser radiation are investigated. The degree of spatial coherence is determined from measurements of the contrast of interference fringe patterns obtained for a tungsten bulb as the light source. It is demonstrated that the degree of spatial coherence of an incandescent lamp is increased by additional excitation of the filament with focused laser radiation. Furthermore, the degree of spatial coherence can be adjusted by selecting the voltage applied to the filament. Such light sources can find applications in imaging techniques where precise control of spatial coherence of illumination is required.

Controlling the Spatial Coherence of an Optical Source Using a Spatial Filter

This paper presents the theory for controlling the spectral degree of coherence via spatial filtering. Starting with a quasi-homogeneous partially coherent source, the cross-spectral density function of the field at the output of the spatial filter is found by applying Fourier and statistical optics theory. The key relation obtained from this analysis is a closed-form expression for the filter function in terms of the desired output spectral degree of coherence. This theory is verified with Monte Carlo wave-optics simulations of spatial coherence control and beam shaping for potential use in free-space optical communications and directed energy applications. The simulated results are found to be in good agreement with the developed theory. The technique presented in this paper will be useful in applications where coherence control is advantageous, e.g., directed energy, free-space optical communications, remote sensing, medicine, and manufacturing.

Ultrafast spatial coherent control methods for transition pathway resolving spectroscopy of atomic rubidium.

We demonstrate the use of the ultrafast spatial coherent-control method to resolve the fine-structure two-photon transitions of atomic rubidium. Counter-propagating ultrafast optical pulses with spectral phase and amplitude programmed with our optimized solutions successfully induced the two-photon transitions through 5S1/2-5P1/2-5D and 5S1/2-5P3/2-5D pathways, both simultaneously and at distinct spatial locations. Three different pulse-shaping solutions are introduced that combine amplitude shaping, which avoids direct intermediate resonances, and phase programming, which enables the remaining spectral components to be coherently interfered through the targeted transition pathways. Experiments were performed with a room-temperature vapor cell, and the results agree well with theoretical analysis.

Nanoscale Spatial Coherent Control over the Modal Excitation of a Coupled Plasmonic Resonator System

We demonstrate coherent control over the optical response of a coupled plasmonic resonator by high-energy electron beam excitation. We spatially control the position of an electron beam on a gold dolmen and record the cathodoluminescence and electron energy loss spectra. By selective coherent excitation of the dolmen elements in the near field, we are able to manipulate modal amplitudes of bonding and antibonding eigenmodes. We employ a combination of CL and EELS to gain detailed insight in the power dissipation of these modes at the nanoscale as CL selectively probes the radiative response and EELS probes the combined effect of Ohmic dissipation and radiation.

Coherent control of resonant two-photon transitions by counterpropagating ultrashort pulse pairs

We describe optimized coherent control methods for two-photon transitions in atoms of a ladder-type three-state energy configuration. Our approach is based on the spatial coherent control scheme which utilizes counter-propagating ultrashort laser pulses to produce complex excitation patterns in an extended space. Since coherent control requires constructive interference of constituent transition pathways, applying it to an atomic transition with a specific energy configuration requires specially designed laser pulses. Here, we show, in an experimental demonstration, that the two-photon transition with an intermediate resonant energy state can be coherently controlled and retrieved out from the resonance-induced background, when phase-flipping of the laser spectrum near the resonant intermediate transition is used. A simple reason for this behavior is the fact that the transition amplitude function (to be added to give an overall two-photon transition) changes its sign at the intermediate resonant frequency, thus, by a proper spectral-phase programming, the excitation patterns (or the position-dependent interference of the transition given as a consequence of the spatial coherent control) are well isolated in space along the focal region of the counter-propagating pulses.

Coherence characteristics of random lasing in a dye doped hybrid powder

The photon statistics of the random laser emission of a Rhodamine B doped di-ureasil hybrid powder is investigated to evaluate its degree of coherence above threshold. Although the random laser emission is a weighted average of spatially uncorrelated radiation emitted at different positions in the sample, a spatial coherence control was achieved due to an improved detection configuration based on spatial filtering. By using this experimental approach, which also allows for fine mode discrimination and time-resolved analysis of uncoupled modes from mode competition, an area not larger than the expected coherence size of the random laser is probed. Once the spectral and temporal behavior of non-overlapping modes is characterized, an assessment of the photon-number probability distribution and the resulting second-order correlation coefficient as a function of time delay and wavelength was performed. The outcome of our single photon counting measurements revealed a high degree of temporal coherence at the time of maximum pump intensity and at wavelengths around the Rhodamine B gain maximum.

Spatial and Spectral Coherent Control over Direct Frequency Comb Excitation

We demonstrate a method for spatial control over two-photon excitation, by using counter-propagating frequency comb pulse trains. This type of control is shown to enable significant improvement for direct frequency comb spectroscopy.

Spatial and spectral coherent control with frequency combs

Quantum coherent control (1-3) is a powerful tool for steering the outcome of quantum processes towards a desired final state, by accurate manipulation of quantum interference between multiple pathways. Although coherent control techniques have found applications in many fields of science (4-9), the possibilities for spatial and high-resolution frequency control have remained limited. Here, we show that the use of counter-propagating broadband pulses enables the generation of fully controlled spatial excitation patterns. This spatial control approach also provides decoherence reduction, which allows the use of the high frequency resolution of an optical frequency comb (10,11). We exploit the counter-propagating geometry to perform spatially selective excitation of individual species in a multi-component gas mixture, as well as frequency determination of hyperfine constants of atomic rubidium with unprecedented accuracy. The combination of spectral and spatial coherent control adds a new dimension to coherent control with applications in e.g nonlinear spectroscopy, microscopy and high-precision frequency metrology.

Spatial coherence control of xuv supercontinuum generation by two-color laser field

We investigate the spatial characteristics of xuv supercontinuum generation in the two-color laser field consisting of a fundamental and a weak second harmonic field. By optimizing the synthesized two-color field, the spatial profile of the xuv supercontinuum varies from annular-like to Gaussian-like and then the spatial quality is improved effectively, which is beneficial for its potential applications. Moreover, our calculation shows that the spatial quality of the supercontinuum is stable when the intensity of the controlling field varies in the acceptable fluctuation.

基于空间相干性控制的环形光源技术

基于空间相干性控制的环形光源技术

Improved illumination system for spatial coherence control

An improved illumination system is proposed for creating a temporally coherent and spatially incoherent extended source to be used for spatial coherence control and reconstruction of a coherent hologram. Taking into account the fact that a rotating ground glass does not behave as an ideal Lambertian diffuser, the new illumination system tailors the directivity of the scattered lights to direct the lights efficiently into an interferometer so that a spatial coherence function can be better controlled and detected with higher fidelity. Experimental results are presented that demonstrate improved performance of the proposed system.

Control of radiation spatial coherence under synchronous amplification in crystalline LiF:F 2 − amplifier

A technique of spatial coherence control, based on the synchronous amplification of a radiation in LiF crystals with F −2 color centers, is demonstrated. Spatial radiation distributions of stimulated Raman scattering (SRS) in oxide crystals were investigated under picosecond laser excitation. Low spatial radiation coherence was revealed for both the transient and quasi-stationary SRS. Spatially incoherent SRS was transformed to spatially coherent radiation as a result of phase—locked picosecond synchronous laser pumping of nonlinear Raman and LiF: F −2 crystals and the Stokes radiation amplification in the color center crystal.

Speckle reduction in coherent information processing

Speckle reduction techniques have been developed as one of the most active research fields in coherent optical information processing, together with the investigations of speckle statistics and coherence theory. The principles of speckle reduction are classified to five categories: 1) control of spatial coherence, 2) control of temporal coherence, 3) spatial sampling, 4) spatial averaging, and 5) digital image processing. This paper surveys the research works in the field of speckle reduction techniques involving four categories 1)-4) which have been conducted in the past 30 years.

Control of mutual spatial coherence of temporal features by reflexive photorefractive coupling

We analyze reflexive photorefractive coupling of an information-bearing beam carrying several distinct spatiotemporal features, with emphasis on the coupling-induced change in the mutual spatial coherence. We formulate equations describing evolution of the mutual correlation functions between different features and discuss their solutions both in the full two-dimensional case and in the limit leading to a one-dimensional description of the reflexive coupling geometry.

System of rays in lasers and a new feasibility of light coherence control

New optical characteristics of a laser cavity equipped with a multilobe mirror consisting of many tilted planes are under consideration. New models based on examination of binomial and trinomial distributions are proposed to describe light ray propagation in this cavity. New experimental results of spatial coherence control and a possibility of temporal coherence control of laser radiation are shown, too.

Two-dimensional control of optical spatial coherence by acoustooptic interactions

A method is described for 2-D control of spatial coherence by use of multiple, crossing ultrasonic waves. If all the ultrasonic waves differ in frequency from one another, the coherence modification factor results as a product of the individual modification factor formed by each ultrasonic wave itself. Two arrangements are discussed in detail together with experimental results: one with the ultrasonic waves propagating in orthogonal directions, the other with the waves propagating in three symmetric directions. The coherence modification factor obtained from either arrangement varies periodically in space but is almost uniform in the azimuthal direction if the two-point separation concerned is taken in a linear dimension a little larger than half of one ultrasonic wavelength.