High-speed scattering medium characterization with application to focusing light through turbid media

Abstract

We introduce a phase-control holographic technique to characterize scattering media with the purpose of focusing light through it. The system generates computer-generated holograms implemented via a deformable mirror device (DMD) based on micro-electro-mechanical technology. The DMD can be updated at high data rates, enabling high speed wavefront measurements using the transmission matrix method. The transmission matrix of a scattering material determines the hologram required for focusing through the scatterer. We demonstrate this technique measuring a transmission matrix with 256 input modes and a single output mode in 33.8 ms and creating a focus with a signal to background ratio of 160. We also demonstrate focusing through a temporally dynamic, strongly scattering sample with short speckle decorrelation times.

Controlling waves in space and time for imaging and focusing in complex media

“…Phase-conjugation experiments in vivo have provided a weak signal that persists for less than a second 115 . Several groups have recently demonstrated wavefront shaping and transmission matrix measurements [116][117][118] at optimization speeds 100 times faster than first-generation experiments 39 . This advance could allow deep imaging using two-photon excitation.…”

Quantum-secure authentication of a physical unclonable key

“…Using faster micromirror-based SLMs [21,22], the complete authentication protocol with 20 repetitions can be performed in less than a millisecond. The one-time enrollment of the key then takes of the order of a second.…”

Wavefront Shaping and Its Application to Enhance Photoacoustic Imaging

“…This technique is based on the so-called PA effect [16][17][18], which mainly consists of four steps: first, tissue molecules in the region of interest (ROI) within the sample absorb pulsed light (no matter if it is in ballistic or diffusive form); the absorbed optical energy is converted to heat, causing local the temperature to increases; ultrasonic waves are generated due to thermal expansion; finally, these ultrasonic waves (typically around the order of MHz if the exiting light pulse width is several nanoseconds) can be detected by one or a series of ultrasound transducers mounted outside the sample. Since ultrasonic waves are scattered almost 1000 times less than light is in tissue (unless otherwise mentioned, we always mean soft tissue in the context), they can be used to reconstruct an image of the absorbing ROI with an acoustic resolution [19][20][21][22][23][24][25][26][27]. As the generation of such PA signals does not distinguish ballistic or diffusive exciting light formations, it allows for a penetration depth far exceeding the optical diffusion limit.…”

“…However, recently, researchers began to notice that the seemingly random scattering events and the resultant speckles are actually deterministic within a certain temporal window [37,38], and it is possible to reverse [39][40][41] or compensate for [42] the scattering-induced phase scrambling. To do so, researchers have developed several wavefront shaping (sometimes also referred to wavefront engineering) techniques, such as iterative wavefront optimization [23][24][25][26]28,[42][43][44][45][46][47][48][49][50][51], measuring the transmission matrix of the scattering medium [21,22,[52][53][54][55][56], and optical time reversal via phase conjugation [39,40,[57][58][59][60][61][62][63][64][65]. Nevertheless, the goals of these implementations are identical, i.e., to make light wavelets traveling along different optical paths interfere coherently at a region of interest (ROI) and form a bright optical spot (focus) out of the much darker background.…”