N. Treps

Surpassing the Standard Quantum Limit for Optical Imaging Using Nonclassical Multimode Light

Using continuous wave superposition of spatial modes, we demonstrate experimentally displacement measurement of a light beam below the standard quantum limit. Multimode squeezed light is obtained by mixing a vacuum squeezed beam and a coherent beam that are spatially orthogonal. Although the resultant beam is not squeezed, it is shown to have strong internal spatial correlations. We show that the position of such a light beam can be measured using a split detector with an increased precision compared to a classical beam. This method can be used to improve the sensitivity of small displacement measurements.

Increasing image resolution in near-infrared to visible upconversion detection for long-range active imaging

Near-infrared imaging InGaAs sensors show lower performances in term of noise and sensitivity compared to silicon based cameras. Image frequency conversion from near-infrared to visible wavelengths by nonlinear parametric sumfrequency mixing in a χ(2) medium should increase detection performances in active imaging applied to long range target identification. For such applications, both energy conservation and phase matching conditions are ideally suited to efficient upconversion. Nevertheless, the available resolution still hampers the development of upconversion imagers. In this paper, we upconvert images provided by 1.5 μm collimated continuous wave lasers illuminating resolution targets and small objects. Using a 2.7 nm wide pump spectrum at 1064 nm, we resolve 56x64 spatial elements whereas we obtained only 16x19 spatial elements with a narrow spectrum pump laser at 1064 nm with the same beam diameter and 8x8 spatial elements with a 0.5 mm thick crystal. These results are compatible with long range target recognition. A laboratory scale experiment of active imaging of diffusive objects is shown as an illustration.

Quantum uncertainty in the beam width for optical spatial modes

We theoretically investigate the quantum uncertainty in the width of optical beams. Many optical applications such as imaging and beam focusing are limited by the quantum noise in spatial characteristics of light beams.

Tools for Spatial Multimode Quantum Optics

The spatial properties of laser beams can be used to encode, transfer and detect quantum information into high order modes with high efficiency. We demonstrate the use of such states, including spatial squeezing and entanglement.