Effect of experimental parameters on optimal transmission of light through opaque media

Spatial light modulator (SLM) controlled transmission of light through opaque media is a relatively new experimental method with wide applications in various fields. While there has been a surge in research into the technique, there has been little work reported considering the effects of various experimental parameters on the efficiency of optimization. In this study, we explore the effects of various experimental conditions on optimization and find that the intensity enhancement depends on the number of modulated channels, number of phase steps, feedback integration radius, beam spot size, and active SLM area. We also develop a model, based on the propagation of a Gaussian beam with a random phase front, to account for most of the measured effects.

Figure 1

Camera image (a) before and (b) after optimization. The image before optimization is dim and random, while afterwards the beam is focused into a tight spot. The camera pixel size is $5.2 \mu \mathrm{m}$ and the exposure time is 2 ms for the dim image and 0.127 ms for the optimized image.

Figure 2

Modeled intensity enhancement as a function of inverse squared bin spacing. Without noise, the enhancement follows a power function, while with noise, the enhancement behaves as an exponential.

Figure 3

Modeled intensity enhancement as a function of inverse squared bin spacing for different $M$ values. The enhancement follows an exponential function with the amplitude changing with $M$ while the shape parameter remains constant.

Figure 4

Modeled intensity enhancement as a function of active SLM side length. The enhancement is found to follow a Gaussian function.

Figure 5

Intensity enhancement as a function of the number of phase steps.

Figure 6

Modeled intensity enhancement as a function of squared integration radius for four different bin numbers. The enhancement is found to follow a double exponential decay.

Figure 7

Modeled intensity enhancement as a function of beam diameter. The enhancement is found to be a peaked function, with the peak location being inversely related to the integration radius used. This result is consistent with the Fourier relationship between the sample and detector planes.

Figure 8

Optical setup schematic.

Figure 9

Intensity enhancement as a function of squared inverse bin size. The enhancement is found to follow an exponential function, which is consistent with the RPGBM results.

Figure 10

Measured intensity enhancement as a function of the quartic active side length, $L^4$. The enhancement is found to follow an exponential function, which is different than predicted by the RPGBM.

Figure 11

Intensity enhancement as a function of phase steps.

Figure 12

Intensity enhancement as a function of integration radius measured using ground glass with 32 phase steps, a spot size of $380 \mu \mathrm{m}$, and four different total number of bins. The enhancement is found to behave as a double exponential, which is consistent with the RPGBM.

Figure 13

Peak enhancement as a function of position along the optical axis, where $z=0$ is the focal point of the focusing lens. The spot size at $z=0$ is $\approx 0.9 \mu \mathrm{m}$.

Figure 14

Measured intensity enhancement as a function of the on-sample spot size. The enhancement is found to follow a peaked function with the peak location being inversely dependent on the integration radius, consistent with the RPGBM result.