Beyond intensity modulation: new approaches to pump-probe microscopy

Abstract

Pump-probe microscopy is an emerging nonlinear imaging technique based on high repetition rate lasers and fast intensity modulation. Here we present new methods for pump-probe microscopy that keep the beam intensity constant and instead modulate the inter-pulse time delay, the relative polarization, or the pulse length. These techniques can improve image quality for samples that have poor heat dissipation or long-lived radiative states, and can selectively address nonlinear interactions in the sample. We experimentally demonstrate this approach and point out the advantages over conventional intensity modulation.

Contrast mechanisms in pump-probe microscopy of melanin

“…We recently reported polarization modulation pump-probe microscopy and demonstrated that polarization modulation can be used to experimentally separate two molecular species [21]. Here we use a similar approach, based on a simple dipole transition model, to utilize polarization dependence for identification of molecular processes in melanin.…”

“…This has the advantage that the result will be independent of the overall amount of melanin present in the sample. We assume the polarization dependence of GSB1 (for both particles and subunits) and GSB2 to be the same, see free fit parameters in table 2, with 𝑏 = 1, 𝑐 = 0.5 and 𝛼 = 0, which reflects the polarization dependence of GSB in a simple dipole transition model [21]:…”

Roadmap on Label‐Free Super‐Resolution Imaging

“…Such light–matter interactions provide molecular contrast without needing exogenous labels and preserve the local biochemical environment of the target molecules. [ 468 ] In general, they involve the second χ 2 and third χ 3 order of susceptibilities. [ 469 ] Transient absorption is related to third‐order non‐linearity susceptibility but rarely implicates fluorescence emission.…”