The GoSwift project is a collaboration between Texas A&M, NASA, Boeing and the University of Michigan with the goal of reducing the perceived loudness of sonic booms from commercial supersonic aircraft using an adaptive morphing structure on the aircraft. The project utilizes a sense-think-act approach. First, atmospheric conditions relevant to the propagation of the sonic boom are measured between the aircraft and the ground using an on-board lidar system. Using the measured atmospheric conditions and flight telemetry, an on-board computer determines the optimal shape of the morphing structure to reduce the loudness of the sonic boom. Finally, the morphing structure is adjusted. The lidar and morphing structure system will be tested on an F15. The project currently passed the mission concept review (MCR) and system requirements review (SRR). The preliminary design review (PDR) is expected to occur in Fall 2027.
As part of the GoSwift project, the ALLEMO lab is responsible for developing a lidar system to obtain a temperature profile of the atmosphere. The system produces a pulsed 387 nm probe beam (resonant with the 6S to 8P cesium absorption line) by frequency quadrupling the output from an erbium amplifier. The spectral width of the backscattered Rayleigh signal is dependent on the temperature of the air. The signal is collected, split and propagated through two cesium cells of different optical depths. The temperature of the air is estimated by comparing the transmission intensity through the two cells. Ground testing uses the AURa lidar system (link to lidar page https://allemo.engr.tamu.edu/facility/).
Project: Frequency Up-conversion Via Four Wave Mixing
Frequency up-conversion is the process of converting low frequency (IR, red, green) to high frequency (blue, UV) light. Here green 532 nm light is converted to blue 420 nm light through resonant photon interactions corresponding to energy level transitions in a rubidium vapor. Two beams at 795 nm and 1320 nm co-propagate with the collimated 532 nm signal, exciting atoms in the vapor to the 6P state through three photon resonance. When the atoms decay back to the ground state, they emit collimated 420 nm light. The goal of this project is to develop a narrow bandpass filter (~ 1 GHz spectral width) for green light near the second harmonic Nd:YAG wavelength. Aligning the signal light to be resonant with the rubidium energy level transition up-converts the signal of interest to blue light while ignoring non-resonant background light.
Publication: Randolph, R., Finberg, E., and Miles, R. “Green to Blue Light Conversion through Resonant Four Wave Mixing in Rubidium Vapor.” Optics & Laser Technology, Vol. 195, 2025, p. 114508. https://doi.org/10.1016/j.optlastec.2025.114508.
Figure: (a) Rubidium energy levels and wavelengths associated with the four wave mixing process. (b) Schematic of bandpass filter using frequency up-conversion.
Figure: Schematic of four wave mixing process. Pictures show light fluorescing from the rubidium cell, a profile of the generated 420 nm signal, and the image of an “A” up-converted from green to blue light.
