About 10x faster image acquisition and two orders of magnitude faster tuning in SRS microscopy including the fingerprint region of relevant biological samples

Ingo Rimke^a, Gero Stibenz^a, Stefan Popien^a, Peter Trabs^a, Lenny Reinkensmeier^b, Rene Siegmund^b, Alexander Egner^b, Sandro Heuke^c

^a APE Angewandte Physik & Elektronik GmbH, Berlin 13053, Germany

^b Department of Optical Nanoscopy, Institute for Nanophotonics Göttingen, Göttingen, Germany

^c Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, Marseille 13013, France

We have successfully developed an advanced light source tailored for Coherent Raman microscopy and other nonlinear microscopy modalities, including SHG and multiphoton fluorescence. In comparison to the prevailing SRS light source available in the market (APE’s picoEmerald S [1]), our innovative solution offers several notable enhancements.

One prominent advantage of the new light source lies in its significantly accelerated tuning speed. We have achieved a 100-fold increase for random wavelength access, including laser output power control and dispersion compensation. Switching to different Raman bands now takes about 1 second. As is state of the art, the light source setup includes both spatial and temporal overlap of Stokes and Pump laser beams to provide the application with a single laser beam. The temporal overlap can automatically adjust to the dispersion properties of the external optical setup (microscope).

To speed up image acquisition and improve signal, we have changed the repetition rate from 80 MHz to 40 MHz, resulting in doubled pulse energy. This in combination with a subharmonic modulation frequency of 20 MHz leads to a significant reduction of the pixel dwell time. The theoretical improvement is a factor of 8 all while maintaining the same Signal-to-noise ratio within the image [2]. The laser is based on proven solid state OPO technology and thus intrinsically shot noise limited from 5 MHz onwards. The output pulse lengths and bandwidths of 2 ps and about 10 cm-1 respectively combine optimum spectral resolution with high sensitivity.

The OPO’s redesigned optical cavity also allows for a wider wavelength coverage. The Signal beam is now tunable from 660 nm to 1020 nm (up from previously 700 nm to 990 nm) which corresponds to an Idler tuning range of 1040 nm to 2340 nm (up from 1080 nm to 1950 nm). To enhance SHG and TPF efficiencies even further, the new light source now allows to selectively increase the output bandwidth, which offers the opportunity to compress the pulse duration down to a few 100 fs.ICOPVS-P-06

We directly compare the image quality of the two light sources side by side coupled into the same microscope and will present CH- and fingerprint images of relevant biological samples.