Quantum dots are typically formed from large groupings of atoms and thus may be expected to have appreciable many-body behavior under intense optical excitation. Nonetheless, they are known to exhibit discrete energy levels due to quantum confinement effects. We show that, like single-atom or single-molecule two- and three-level quantum systems, single semiconductor quantum dots can also exhibit interference phenomena when driven simultaneously by two optical fields. Probe absorption spectra are obtained that exhibit Autler-Townes splitting when the optical fields drive coupled transitions and complex Mollow-related structure, including gain without population inversion, when they drive the same transition. Our results open the way for the demonstration of numerous quantum level-based applications, such as quantum dot lasers, optical modulators, and quantum logic devices.

https://science.sciencemag.org/content/sci/317/5840/929.full.pdf

Coherent optical spectroscopy of a strongly driven quantum dot.

Photons are efficiently funnelled into a single molecule if they are nearly resonant with the sharp molecular transition. In this condition, the coherent nonlinear optical effect can be induced with only a few photons without high-finesse cavities.

/pdf/few-photon-coherent-nonlinear-optics-with-a-single-molecule-g0dj9ffsnq.pdf

Few-photon coherent nonlinear optics with a single molecule

Low-cost complex plastic optics allow biocular viewing of video images generated by a single electro-optic display device, such as in a head-mounted display (HMD) for commercial or medical viewing applications. A dual off-axis configuration uses nearly collimated illumination optics and intermediate imaging optics to fill both eyepieces from a single display device without the need for a beamsplitter. Multiple illumination schemes are provided for either monochrome or color, and in either two-dimensional or time-sequential true stereographic presentation. Light from multicolor sources is superimposed, mixed, and homogenized by mixing light cones with diffractive collectors. Offsetting color overcorrection and undercorrection of individual optical elements achieves overall chromatic correction with minimal optical element complexity. A wireless video signal interface eliminates excess cabling. Additional features include lightweight achromatic eyepiece construction and interchangeable lenslets for peripheral vision correction. Multiple optical elements are injection-molded as a unitary plastic structure, thereby reducing cost and complexity.

Biocular viewing system with intermediate image planes for an electronic display device

Dynamic Bragg gratings can be recorded in rare-earth (e.g. Er, Yb) doped optical fibres by two counter-propagating mutually coherent laser waves via local saturation of the fibre optical absorption or gain (in optically pumped fibres). Typical recording cw light power needed for efficient grating formation is of sub-mW–mW scale which results in characteristic recording/erasure times of 10–0.1 ms. This review paper discusses fundamental aspects of the population grating formation, their basic properties, relating wave-mixing processes and also considers different applications of these dynamic gratings in single-frequency fibre lasers, tunable filters, optical fibre sensors and adaptive interferometry.

https://iopscience.iop.org/article/10.1088/0022-3727/41/22/224002/pdf

Dynamic population gratings in rare-earth-doped optical fibres

All known polarizers operate through a separation of orthogonal electric field components, one of which is subsequently discarded. As a result, 50% of the unpolarized incident light is wasted in the process of conversion to polarized light. We demonstrate a new method by which we use the optical power in the ordinarily discarded component as the pump to amplify the retained component through photorefractive two-beam coupling to achieve greater than 50% throughput.

Conversion of unpolarized light to polarized light with greater than 50% efficiency by photorefractive two-beam coupling.

We present the results of an experimental and theoretical study of the gain (or absorption) experienced by a weak probe beam propagating through a sodium vapor in the presence of an intense pump field that is nearly resonant with the 3s → 3p atomic transition. The probe-transmission spectrum includes three distinct features that result from the modification of the atomic-level structure by the ac-Stark effect. Two of these features can lead to amplification of the probe wave. We measured the dependence of the probe spectrum on the detuning of the pump beam from resonance and on the pressure of a helium buffer gas. The experimentally obtained spectra are in good agreement with the predictions of a theoretical model based on the solution of the density-matrix equations of motion for a two-level atom and including the effects of Doppler broadening. The maximum gain measured in these experiments occurs at one of the Rabi sidebands and leads to a 38-fold increase in the intensity of the probe wave. Under some experimental conditions, we also observed two additional resonances, which are due to stimulated Raman scattering involving the sodium ground-state hyperfine levels.

Induced gain and modified absorption of a weak probe beam in a strongly driven sodium vapor

An analytic solution for the intensity distribution of two counterpropagating pump waves within a saturable absorber is derived. From this distribution, the spatial variation of the nonlinear absorption and coupling constants that appear in the coupled-amplitude equations for the probe and the signal (i.e., conjugate) waves are determined. These coupled-amplitude equations are solved numerically in a noniterative manner, leading to a prediction for the phase-conjugate reflectivity. The results of the exact theory are compared with those of previously published theories. It is found that at large values of the input-pump intensities, the predicted phase-conjugate reflectivity is larger when pump-absorption effects are included in the theory.

Exact theory of pump-wave propagation and its effect on degenerate four-wave mixing in saturable-absorbing media

Nd3+ beta″ alumina is one of a family of potentially useful nonlinear-optical materials based on rare-earth ions substituted into a beta″ alumina host. The saturation intensity of Nd3+ beta″ alumina has been measured to be in the range 16 to 35 kW cm−2. Phase conjugation by degenerate four-wave mixing has been demonstrated, and the phase-conjugate reflectivity has been measured as a function of both laser wavelength and intensity.

Saturated absorption and degenerate four-wave mixing in Nd3+ BETA-double prime alumina.

The phase-conjugate reflectivity attainable by degenerate four-wave mixing in an idealized saturable absorbing medium is calculated for arbitrary values of the laser intensity, laser frequency, and absorption path-length of the nonlinear medium. The influence of pump-wave absorption, including saturation and standing-wave effects, is included in the theory. The treatment is based on an analytic expression for the intensity distribution of the counterpropagating waves. The theoretical predictions differ substantially from those based on theories that ignore pump absorption effects. The results of the present calculation are used to predict the minimum laser intensity, absorption path-length, and detuning required to obtain unit reflectivity and self-oscillation.

Mark T. Gruneisen

Papers

Induced gain and modified absorption of a weak probe beam in a strongly driven sodium vapor

Exact theory of pump-wave propagation and its effect on degenerate four-wave mixing in saturable-absorbing media

Saturated absorption and degenerate four-wave mixing in Nd3+ BETA-double prime alumina.

Theory of degenerate four-wave mixing in saturable absorbing media with the inclusion of pump propagation effects

Energy transfer between laser beams propagating through an atomic vapor.