Past advances in CARS microscopy have been possible due to the constant improvement in ultrafast laser sources. This development continues today to push CARS technology to the next level, and thus fulfills the demands of emerging applications in cellular biology and biomedical science.

Past: Two tightly synchronized Mode-locked Ti:Sapphire lasers:

Pros:

• High spectral resolution (1-3 cm -1 for 5ps pulse)
• Broad Tunability (500-3500cm^-1)

• one of the lasers can be fs-converted for multiplex-imaging

Room for improvement:

• Timing jitter limits the ultimate performance
• Complex: two laser sources
• The system has short operation wavelengths in the IR (690 - 1080 nm). Longer operation wavelengths are desired to increase the penetration depth and reduce photodamage.

Present: Synchronously-pumped Optical Parametric Oscillator (OPO)
Nd:Vanadate laser provides up to 18W of 1064nm light that can partially be frequency doubled to 532nm to synchronously pump an OPO. The OPO produces tunable, collinear and temporally overlapped signal (700nm to 1000nm) and idler beams (1140nm-2100nm).
This light source allows two mode of operation:

• Signal-1064nm-excitation: Idler-beam is blocked with filter and signal and 1064nm-beam are overlapped with a dichroic beam-combiner. The timedelay between the beams has to be set once but is stable over time due to synchronous pumping. The shorter wavelength offer higher spatial resolution and higher detector sensitivity for low wav numbers.

• Signal-idler-excitation: Signal- and Idler-beam are automatically overlapped in time and space and thus offer straight forward operation. The longer wavelength offer higher penetration depth and create less photodamage.

Automated OPO tuning allows SRS or CARS microspectroscopy.