Novel nonlinear contrast improves deep-tissue microscopy
Femtosecond laser pulse and pulse-train shaping allow detection of new nonlinear effects, with modest powers, making new biomarkers accessible and permitting deeper tissue imaging than conventional microscopy. The most developed of these technique create light at a new wavelength, which can then be separated from the exciting laser. While the two photon fluorescence (TPF) can be induced by continuous wave lasers, the vast majority of studies use short laser pulses to achieve high peak power with relatively low tissue damage from average power dissipation. Two photon absorption (TPA) and self-phase modulation (SPM) are the two most important single-wavelength effect for the purpose of tissue engineering. TPA is more effective on the intense pulses than on the weak ones, and it thus distorts the amplitude modulation, creating extra sidebands. Microscopic resolution to depths of about 1mm should be achievable in most tissues with far more physiological contrast than conventional microscopy.
Warren, WS; Fischer, MC; Tong, Y
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