Stefano Bonora

Optimization of two-photon wave function in parametric down conversion by adaptive optics control of the pump radiation

We present an efficient method for optimizing the spatial profile of entangled-photon wave function produced in a spontaneous parametric down conversion process. A deformable mirror that modifies a wavefront of a 404xa0nm CW diode laser pump interacting with a nonlinear β-barium borate type-I crystal effectively controls the profile of the joint biphoton function. The use of a feedback signal extracted from the biphoton coincidence rate is used to achieve the optimal wavefront shape. The optimization of the two-photon coupling into two, single spatial modes for correlated detection is used for a practical demonstration of this physical principle.M. Minozzi, S. Bonora, A. V. Sergienko, G. Vallone, and P. Villoresi Department of Information Engineering, University of Padova, Via Gradenigo, 6/B, 35131, Padova, Italy Institute for Photonics and Nanotechnology, Nat. Res. Council, Via Trasea, 7, 35131, Padova, Italy Department of Electrical and Computer Engineering, and Photonics Center, Boston University, 8 Saint Marys Street, Boston, Massachusetts 02215

Active diffraction gratings: Development and tests

We present the realization and characterization of an active spherical diffraction grating with variable radius of curvature to be used in grazing-incidence monochromators. The device consists of a bimorph deformable mirror on the top of which a diffraction grating with laminar profile is realized by UV lithography. The experimental results show that the active grating can optimize the beam focalization of visible wavelengths through its rotation and focus accommodation.

Adaptive optics on small astronomical telescope with multi-actuator adaptive lens

Adaptive Optics (AO) is a key technology for ground-based astronomical telescopes, allowing to overcome the limits imposed by atmospheric turbulence and obtain high resolution images. This technique however, has not been developed for small size telescopes, because of its high cost and complexity. We realized an AO system based on a Multi-actuator Adaptive Lens and a Shack-Hartmann wavefront sensor (WFS), allowing for a great compactness and simplification of the optical design. The system was integrated on a 11” telescope and controlled by a consumer-grade laptop allowing to perform Closed-Loop AO correction up to 400 Hz.

Adaptive optics plug-and-play setup for high-resolution microscopes with multi-actuator adaptive lens

Adaptive Optics (AO) has revealed as a very promising technique for high-resolution microscopy, where the presence of optical aberrations can easily compromise the image quality. Typical AO systems however, are almost impossible to implement on commercial microscopes. We propose a simple approach by using a Multi-actuator Adaptive Lens (MAL) that can be inserted right after the objective and works in conjunction with an image optimization software allowing for a wavefront sensorless correction. We presented the results obtained on several commercial microscopes among which a confocal microscope, a fluorescence microscope, a light sheet microscope and a multiphoton microscope.

Multi-actuator adaptive lens in astronomy: in lab test results

Multi-actuator Adaptive Lenses have been recently utilized for the implementation of Adaptive Optics in different scientific fields such as microscopy, in vivo ophthalmic imaging applications or high power laser beam shaping. A multi-actuator adaptive lens is composed by two thin glass plates bonded to two piezoelectric rings with 18 actuators. The space between the two glass plates is filled with a transparent liquid and the actuation of the lens allows a wavefront modulation up to the 4th order of Zernike polynomials with a relatively fast time response (frequency up to 200Hz). These features allow using the adaptive lens in closed loop with wavefront sensor as if it were a deformable mirror. Despite the adaptive lenses performances do not allow their use in extreme astronomical instrumentation as substitutes for deformable mirrors, they are the ideal device for the correction of the non-common path aberrations in order to maximize the performances of the pyramid wavefront sensor. In this paper, we present the laboratory results of a characterization campaign of an adaptive lens prototype manufactured for astronomical applications and its use to correct non-common path aberrations to enhance pyramid wavefront sensor sensitivity.

Developing an EUV multilayer adaptive mirror: the first results

The growing interest in the study of the extreme ultraviolet (EUV) radiation-matter interaction is feeding up the development of new technologies able to overcame some current technological limits. Adaptive optics is an established technology already widely used for wavefront correction in many applications such as astronomical telescopes, laser communications, high power laser systems, microscopy and high resolution imaging systems. Although this technology is already exploited in the EUV and X-ray range, its usage is only feasible in systems with a grazing incidence configuration. On the other hand, the development of a EUV normal incidence adaptive optics can open new interesting possibilities in many different fields ranging from free electron laser and synchrotron applications up to EUV photolithography. In this work we report the preliminary results achieved in the developing of a normal incidence EUV multilayered adaptive mirror tuned at 30.4nm. The proper functioning and potential applications of such device have been demonstrated by using a High order Harmonics Generation (HHG) source.

Biphoton Generation with an Optimized Wavefront for Free-Space Propagation by means of Adaptive Optics

The pump wavefront which generates photon pairs by spontaneous parametric down conversion is optimized using a feedback which optimize the coincidence count after propagation along a suitable path. The active element is a deformable mirror.

Adaptive Optics Control of the Propagation of Biphoton Wavepacket

Entangled photon pairs are generated with optimal pump wavefront to achieve a desirable free-space propagation. The optimization exploits a closed loop including a deformable mirror, the nonlinear crystal, the propagation line and the single-photon coincidences.

Engineering Multiparameter Entangled State with Adaptive Optics

We discuss the possibility of actively manipulating entangled states generated by type-II parametric down conversion. We study what effect active manipulation of wavevector using adaptive mirror will have on the behavior of polarization-temporal interference.