Laser Sources

Light Sources for CARS Microscopy: Continuous Evolution

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 fulfill the demands of emerging applications in cellular biology and biomedical science.

PAST

Two tightly synchronized Mode-locked Ti:Sapphire lasers

PROS	ROOM FOR IMPROVEMENT
High spectral resolution (1-3 cm^-1 for 5 ps pulse) Broad Tunability (500-3500cm^-1)	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

Intracavity-doubled synchronously-pumped Optical Parametric Oscillator (OPO)

The pump of the OPO acts as the Stokes beam for the CARS nonlinear process while the output of the OPO acts as the pump beam for the CARS nonlinear process.

PROS	ROOM FOR IMPROVEMENT
Complete elimination of pulse jitter High spectral resolution (1-2 cm^-1) Broad tunability (500-3500 cm^-1). Longer operation wavelengths than previous systems (Stokes: 1064 nm; Pump: 780-920 nm)	Complex: Two laser sources Even longer operation wavelengths are desired to increase penetration depths and reduce photodamage

PROS	ROOM FOR IMPROVEMENT
Single source for both Pump and Stokes Colinear Pump and Stokes beams directly from the OPO. No need for optics to combine the two beams. Raman shift selection controlled by the temperature of a single crystal (500-3800 cm^-1) No pulse jitter High spectral resolution (1-2 cm^-1) Wavelengths available over hundreds of nanometers (740-1450 nm) Long operating wavelengths minimize sample photodamage and increase penetration depth	Some detectors cannot be used due to poor red sensitivity

PROS

ROOM FOR IMPROVEMENT

Single source for both Pump and Stokes
Colinear Pump and Stokes beams directly from the OPO. No need for optics to combine the two beams.
Raman shift selection controlled by the temperature of a single crystal (500-3800 cm^-1)
No pulse jitter
High spectral resolution (1-2 cm^-1)
Wavelengths available over hundreds of nanometers (740-1450 nm)
Long operating wavelengths minimize sample photodamage and increase penetration depth

Some detectors cannot be used due to poor red sensitivity

FUTURE

We are working on the future of CARS imaging… Surprises are on the way!