Imaging with Nonlinear Optics

Winfried Denk, Lucent Technologies Bell Labs

One of the more surprising applications of femtosecond lasers is the imaging of sensitive biological structures, which appear to tolerate the onslaught of peak power densities of more that 1011 W/cm2, better than the 105 W/cm2 in a confocal or even the mere 500 W/cm2 of conventional widefield illumination. Ultrashort-pulse lasers thus open a new way for fluorescence microscopy in living tissues, reducing the severe photodamage and photobleaching often associated with such experiments.
The instrument that performs this feat is called a multi-photon laser scanning microscope and was invented in 1989 by Denk, Strickler, and Webb. It basically consists of a modified laser scanning microscope with a femtosecond (typically a Ti:Sapphire laser) mode-locked laser as the excitation light source…