Focusing light into scattering media with ultrasound-induced field perturbation

Focusing light into scattering media,although challenging,is highly desirable in many realms.With the invention of time-reversed ultrasonically encoded(TRUE)optical focusing,acousto-optic modulation was demonstrated as a promising guidestar mechanism for achieving noninvasive and addressable optical focusing into scattering media.Here,we report a new ultrasound-assisted technique,ultrasound-induced field perturbation optical focusing,abbreviated as UFP.Unlike in conventional TRUE optical focusing,where only the weak frequency-shifted first-order diffracted photons due to acousto-optic modulation are useful,here UFP leverages the brighter zeroth-order photons diffracted by an ultrasonic guidestar as information carriers to guide optical focusing.We find that the zeroth-order diffracted photons,although not frequency-shifted,do have a field perturbation caused by the existence of the ultrasonic guidestar.By detecting and time-reversing the differential field of the frequency-unshifted photons when the ultrasound is alternately ON and OFF,we can focus light to the position where the field perturbation occurs inside the scattering medium.We demonstrate here that UFP optical focusing has superior performance to conventional TRUE optical focusing,which benefits from the more intense zeroth-order photons.We further show that UFP optical focusing can be easily and flexibly developed into double-shot realization or even single-shot realization,which is desirable for high-speed wavefront shaping.This new method upsets conventional thinking on the utility of an ultrasonic guidestar and broadens the horizon of light control in scattering media.We hope that it provides a more efficient and flexible mechanism for implementing ultrasound-guided wavefront shaping.

Lyapunov-based switched-gain impact angle control guidance

To hit stationary ground targets in specified direction, a nonlinear impact angle control guidance law based on Lyapunov stability theory is proposed. The proposed law ensures the convergence of the heading angle and the miss distance to guarantee a successful engagement. The impact angle can be adjusted by varying a single parameter. And the maximum value of acceleration has been analyzed to get the proper range for control parameter. Considering the achievable impact angle set is limited, an additional phase is added to form a two-phase control strategy.The first phase is to establish a proper initial condition for the second phase, and the second phase is to hit the target with a certain impact angle. An analysis of the proper selection of control parameters to expand the achievable impact angle set is presented. The performance of the proposed guidance law is illustrated with simulations.

Ascent Trajectory Optimization for Air-Breathing Hypersonic Vehicles Based on IGS-MPSP

This paper proposes an improved Generalized Quasi-Spectral Model Predictive Static Programming(GS-MPSP)algorithm for the ascent trajectory optimization for hypersonic vehicles in a complex°ight environment.The proposed method guarantees the satisfaction of constraints related to the state and control vector while retaining its high computational e±ciency.The spectral representation technique is used to describe the control variables,which reduces the number of decision variables and makes the control input smooth enough.Through Taylor expansion,the constraints are transformed into an inequality containing only decision variables,such that it can be added into GS-MPSP framework.By Gauss quadrature collocation method,only a few collocation points are needed to solve the sensitivity matrix,which greatly accelerates the calculation.Subsequently,the analytical expression is obtained by combining the static optimization with the penalty function method.Finally,the simulation results demonstrate that the proposed improved GS-MPSP algorithm can achieve both high computational e±-ciency and high terminal precision under the constraints..