No abstract

Nonlinear optics with structured light can provide a host of important functions for shaping spatail and temproal structure of light, and the most common used one is frequency conversion. In this work, we propose and demonstrate a novel nonlinear toolkit capable of tuning frequency and orbital angular momentum (OAM) of signal beams simultanously, more importantly, it does not change the spatial ampulitude structure of signal. This unique frequency interface is enabled by using a special structured pump called vortex super-Gaussian beam that has a flattop amplitude distribution and tunable vortex wavefront. This technique provides a dual interface of frequency and OAM, and may inspire many potential applications involving OAM beams.

Optical interferometers are pillars of modern precision metrology, but their resolution is limited by the wavelength of the light source, which cannot be infinitely reduced. Magically, this limitation can be circumvented by using an entangled multiphoton source because interference produced by an N-photon amplitude features a reduced de Broglie wavelength 𝝀∕N. However, the extremely low efficiency in multiphoton state generation and coincidence counts actually negates the potential of using multiphoton states in practical measurements. Here, a novel interferometric technique based on structured nonlinear optics is demonstrated, i.e., parametric upconversion of a structured beam, capable of superresolution measurement in real time. The main principle relies in that the orbital angular momentum (OAM) state and associated intramodal phase within the structured beam are both continuously multiplied in cascading upconversion to mimic the superresolved phase evolution of a multiphoton amplitude. Owing to the use of bright sensing beams and OAM mode projection, up to a 12-photon de Broglie wavelength with almost perfect visibility is observed in real time and, importantly, by using only a low-cost detector. The results open the door to real-time superresolution interferometric metrology and provide a promising way toward multiphoton superiority in practical applications.