Frequency comb ptychoscopy: imaging beyond the resolution-delay limit
Abstract
Approved for Public Release:A fundamental problem in science is detecting the spectrum of a remote source. When an object is imaged, spectroscopic information can provide additional information about its composition. For example, hyperspectral imaging systems have been used to assess chemical concentration. However, these systems typically have low (sub-terahertz) resolution. At the same time, higher-resolution systems could, in principle, offer a wealth of additional information. Below gigahertz resolutions, one could begin to observe the objects structural information. Below megahertz resolutions, one could observe its dynamics. Imaging systems arenot created with these resolutions because conventional spectroscopic methods are all limited by a critical tradeoff, the resolution-delay limit. Achieving higher resolutions while preserving sensitivity requires correspondingly larger optical delays, and this quickly becomes infeasible past a certain point. For example, achieving megahertz resolution requires hundreds of meters of optical delay.Our main goal in this program will be to demonstrate a new paradigm for spectroscopic imaging, frequency comb ptychoscopy, that bypasses this limitation. Frequency combs are light sources with a large number of evenly-spaced lines. Interest in combs has exploded in recent years, as a large number of chip-scale comb sources have been produced. While they have been used in a number of exciting new active sensing applications, it has been unclear if they could be used in passive sensing applications. Recently, we were inspired by the heterodyne techniques most commonly used in radio astronomy to develop frequency comb ptychoscopy, a technique that enables broadband comb spectroscopy of remote sources. This is a revolutionary new approach that is entirely unconstrained by the resolution-delay limit and will allow for spectroscopic imaging with kilohertz-level resolutions. It is an enabling technology whose long-term application space is potentially vast and untapped, both in terms of basic science and applications.Though we have verified this technique experimentally at microwave frequencies, it has yet to be demonstrated with optical combs. In this project, we will demonstrate it using combs at three bandsthe terahertz (THz), the mid-wave infrared (MWIR), and the near-infrared (NIR)ultimately using it to create a multi-spectral ptychoscopic imager. The PI has extensive expertise in developing quantum cascade laser (QCL) basedfrequency combs, with a number of the fields key results. We will develop new broadband QCL combs for the THz & MWIR bands and will create electro-optic combs for the NIR band, using the three ptychoscopic systems to perform ultra-high resolution imaging of a remote target.Ptychoscopy can be performed at any region of the electromagnetic spectrum where combs and detectors are available, so we envision that Department of Defense capabilities can be enhanced in a variety of ways. In particular, we anticipate that the THz and millimeter-wave bands will be most valuable for probing the mechanical structure of remote targets, that the longwave-infrared and MWIR bands will be most useful for chemical sensing, and that the NIR and visible bands will excel at Doppler dynamical measurements.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 05, 2021
- Source ID
- N000142112735
Entities
People
- David Burghoff
Organizations
- Office of Naval Research
- United States Navy
- University of Notre Dame