Sean J. Bentley

Recent progress in quantum and nonlinear optical lithography

We review the status of the field of quantum lithography, that is, the use of quantum-mechanical effects to write lithographic features with resolution finer than that achievable according to the Rayleigh criterion. In particular, we first review the original quantum lithography proposal by Boto et al., and we then describe the status of research aimed at realizing this process.

Nonclassical two-photon interferometry and lithography with high-gain parametric amplifiers

Two-photon entangled states have been utilized in many configurations that exploit the novel fourth-order interferometric properties of these states, most recently in a proposal for the achievement of sub-Rayleigh-limit resolution [1]. While the interferometric properties of biphotons have been extensively analyzed under a variety of arrangements, the impact of multiphoton states on these properties has not been extensively explored.

Parametric downconversion vs optical parametric amplification: a comparison of their quantum statistics

The extent to which the intense light generated by an unseeded, high-gain optical parametric amplifier retains the desired quantum statistical properties of the individual photon pairs generated by spontaneous parametric downconversion is analysed. It is shown that certain but not all of these properties are retained, with important implications for applications of quantum optics.

Measurement of the thermal contribution to the nonlinear refractive index of air at 1064 nm

The thermal contribution to the nonlinear refractive index of air at 1.064mum was measured with a high-finesse 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)((th))=(-1.9+/-0.2)x10 (-14) 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.

Spatial patterns induced in a laser beam by thermal nonlinearities

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(beta)p(2), where P is the power stored in the cavity, p is the pressure of the gas, and beta is a material-dependent parameter.

Three-photon absorption for nanosecond excitation in cadmium selenide quantum dots

We experimentally observe saturable absorption and dra- matic three-photon absorption in various colloidal solutions of cadmium selenide quantum dots, with a strong size dependence witnessed for these properties. We also develop a model for the electronic portion of the nonlinearities that illustrates well the trends exhibited by our experi- mental data. The model incorporates six bands three each in the va- lence and conduction bands.

Nonlinear interferometric lithography for arbitrary two-dimensional patterns

A new, relatively simple experimental technique for generating arbitrary, two-dimensional patterns with high visibility and higher resolution than allowed by the Rayleigh criterion has been developed. The theoretical and experimental details of the method, based on repeated phase-coherent interference of four beams on a multiphoton absorber, are described. A sample pattern generated by numerical computer simulation of the technique is also shown.

Transverse instabilities and pattern formation in two-beam-excited nonlinear optical interactions in liquids

We describe observations of various transverse instabilities that occur when two laser beams intersect in nonlinear optical liquids. Patterns that we observe include two types of conical emission and the generation of a linear array of spots. These results can be understood in terms of the physical processes of self-diffraction, two-beam-excited conical emission, and seeded modulational instability.

Arbitrary 2-D Pattern Formation beyond the Rayleigh Limit

A relatively simple new technique to generate arbitrary two-dimensional patterns in a multi-photon absorber with resolution exceeding the Rayleigh limit has been developed. This four-beam interference technique could greatly extend photolithography capabilities.

Three-photon absorption in cadmium selenide quantum dots

The nonlinear optical properties of CdSe quantum dots were studied. Strong three-photon absorption was observed at wavelengths where the dot samples were nearly transparent at low energy levels but at which bulk CdSe is opaque.