Sum frequency generation process for a new astronomical instrument

摘要

We propose an exotic use of sum frequency generation process (SFG) to develop a new kind of high resolution interferometer for astronomical imaging. SFG is well known to be intrinsically a noiseless non linear process of upconversion which permits a wavelength shift. Thereby we propose to shift astronomical MIR and FIR radiation to shorter wavelength where optical fibers and optical components are available and efficient. In order to demonstrate the validity of this method for high resolution imaging, we plan to set up a two-arm upconversion interferometer on the CHARA telescope array (California). Each arm would include an upconversion stage at the focus of telescope. The success of such a project is obviously conditioned by the quality of nonlinear components (waveguided PPLN) in term of efficiency and noise biases. Moreover, coherence study requires the use of identical non linear components which implies manufacturing constraints. To ensure the feasibility of this project, several studies have been conducted. By implementing an upconversion interferometer in laboratory we have recently demonstrated our ability to analyze the coherence properties of a 1550nm signal at visible wavelength. We also have successfully converted astronomical light using one arm of this interferometer at the Hawaie observatory. It showed the capability of our instrument to astronomical observing conditions in photon counting regime. A preliminary mission at CHARA observatory allowed us to check the compatibility of our instrument with the environment onsite and expected photometric levels. From these data we estimate to be able to study the coherence of astronomical target at 1550nm using such an instrument.