Long-distance fluorescence lifetime imaging using stimulated emission

Synchronized subharmonic modulation in stimulated emission microscopy

In this work, we have demonstrated a stimulated emission (SE)-based pump-probe microscopy with subharmonic fast gate synchronization, which allows over an order of magnitude improvement in signal-to-noise ratio. Critically, the alternative way of modulation is implemented with the highest possible frequency that follows the lasers' repetition rate. Its working is based on a homemade frequency divider that divides the repetition frequency (76 MHz) of the Ti:sapphire (probe) laser to half of the repetition frequency, 38 MHz, which is used to synchronously drive the pump laser and to provide the reference signal for the ensuing lock-in detection. In this way, SE can be detected with sensitivity reaching the theoretical (shot noise) limits, with a much lower time constant (0.1 ms) for faster image acquisition.

Sub-diffraction resolution pump-probe microscopy with shot-noise limited sensitivity using laser diodes

We demonstrate the use of intensity-modulated laser diodes to implement pump-probe microscopy and achieved sub-diffraction resolution imaging with shot-noise limited sensitivity with a scheme of balanced detection. This technique has several applications for various types of induced transmission change, including excited-state absorption, ground state absorption bleaching and stimulated emission. By using our technique, biological imaging of mouse T cells and the axons of neurons in the cerebral cortex was demonstrated.

Fluorescence lifetime imaging with pulsed diode laser enabled stimulated emission

We present here a stimulated emission based fluorescence lifetime imaging (FLIM) scheme using a pair of synchronized diode lasers operating at gain switched pulse mode. The two semiconductor lasers, with wavelengths at 635 nm and 700 nm, serve as the excitation and the stimulation light sources for the ATTO647N labeled sample, respectively. FLIM is readily achieved with their relative time delay controlled electronically. The coherent nature of the stimulated emission signal also allows FLIM at long working distance. In this way, a high performance all-semiconductor FLIM module is realized in a flexible, compact, and cost effective configuration.