Self-steering partially coherent beams

Abstract

We introduce a class of shape-invariant partially coherent beams with a moving guiding center which we term self-steering partially coherent beams. The guiding center of each such beam evolves along a straight line trajectory which can be engineered to make any angle with the x-axis. We show that the straight line trajectory of the guiding center is the only option in free space due to the linear momentum conservation. We experimentally generate a particular subclass of new beams, self-steering Gaussian Schell beams and argue that they can find applications for mobile target tracing and trapped micro- and/or nanoparticle transport.

Figure 1. Self-steering of novel beams in free-space.

(a) SSGS beam intensity distribution at several propagation distances for v₀ = (−2, 4). (b) SSGS beam intensity distribution at several propagation distances for v₀ = (0, 0). (c) SSGS beam intensity distribution at several propagation distances for v₀ = (3, −2).

Figure 2

Schematics for generating (a) conventional Gaussian Schell-model source, and (b) self-steering Gaussian Schell source with controllable parameters u₀ and v₀; L₁ and L₂ thin lenses, rotating ground-glass disk (RGGD), Gaussian amplitude filter (GAF).

Figure 3. Experimental evidence of the beam guiding center evolution.

(a) SSGS beam intensity distribution at several propagation distances given the same v₀ = (5, 5) and different values of the initial coherence width. (b) Same as in (a) in the focal plane with σ_c = 0.2 mm and different values of v₀.

Figure 4. Guiding center position R_c as a function of the propagation distance z for three cases (σ_c = 1.0 mm, σ_c = 0.5 mm, σ_c = 0.2 mm) with the same v₀ = (5, 5).

Figure 5. SSGS beam intensity distribution as the beam passes through a 2 × 2 circle hole array in three cases corresponding to different initial coherence widths.