GPC light shaper for speckle-free one- and two-photon contiguous pattern excitation

Abstract

Generalized Phase Contrast (GPC) is an efficient method for generating speckle-free contiguous optical distributions useful in diverse applications such as static beam shaping, optical manipulation and recently, for excitation in two-photon optogenetics. To fully utilize typical Gaussian lasers in such applications, we analytically derive conditions for photon efficient light shaping with GPC. When combined with the conditions for optimal contrast developed in previous works, our analysis further simplifies GPC's implementation. The results of our analysis are applied to practical illumination shapes, such as a circle and different rectangles commonly used in industrial or commercial applications. We also show simple and efficient beam shaping of arbitrary shapes geared towards biophotonics research and other contemporary applications. Optimized GPC configurations consistently give ~84% efficiency and ~3x intensity gain. Assessment of the energy savings when comparing to conventional amplitude masking show that ~93% of typical energy losses are saved with optimized GPC configurations.

GPC light shaping a supercontinuum source

“…Furthermore, the target output shapes could easily be replaced without increasing the fabrication cost or complexity. Light patterns formed with GPC can reach efficiencies of up to 84% in contrast to simple techniques such as rectangular irises [20]. Moreover, the average light intensity in the patterned region is ~3 times larger than the average intensity within the corresponding region of the incident Gaussian.…”

“…By projecting intensity images that visualize phase inputs, the GPC is a fairly straightforward technique with a high light utilization [18]. It can generate a wide variety of patterns [7,[19][20][21] and accommodates various illumination profiles [7,22,23]. With reconfigurable phase inputs from phase-only SLMs, it is an effective laser projection system for dynamic multiple beam optical trapping [19].…”

“…We therefore summarize how to choose optimal phase masks and PCF sizes based on the formulations in [20] -all currently based on π-shifting phase values at the design wavelength. Given a Gaussian beam with a 1/e 2 radius, w 0 , illuminating a phase mask with phase…”

“…It is characterized by the dimensionless η given by By imposing amplitude matching with a synthetic reference wave [7], and that Δr f coincides with the Fourier distribution's first zero crossing (first dark ring) [20], the conditions for optimal contrast and efficiency of the GPC output lead to the following equations ( )…”

“…Equations (4) and (5) [20]. We show how these conditions are used for fabricating static glass filters in section 4.…”