picoEmerald light source for CARS microscopy

As coherent anti-Stokes Raman scattering (CARS) microscopy has moved out of physics labs into life science institutions, the demand for an easy to use and turn-key light source has increased.

APE and High Q Laser have combined their efforts to produce the picoEmerald, a remote controlled, hands-free, one-box CARS light source, providing pump and Stokes pulses perfectly overlapped in space and time.

The picoEmerald comprises a high power picosecond oscillator (1064nm) with a frequency doubler and a synchronously pumped optical parametric oscilator (OPO) in a single housing. The optical modules were optimised by finite element analysis and mechanical stability algorithms (misalignment stability optimisation) to exhibit maximum passive stability. In addition an active resonator control is used, continuously maximising the efficiency of the high power picosecond oscillator and the OPO. The picoEmerald supplies three temporally and spatially overlapping ultrafast pulse trains: 1064nm out of the laser oscillator itself, along with 690-990 nm signal range and 1150-2300nm idler range from the OPO. The wavelength tuning occurs automatically by PC. Due to the use of a synchronously pumped OPO pumped by a mode-locked solid state laser, the pulses show no timing jitter and a very low noise level.

Best spectroscopic resolution requires a picosecond excitation with a typical bandwidth of ~10cm-1. The picoEmerald delivers 7ps at 1064nm, and 5-6ps from the OPO in order to match this requirement.

Independent power adjustments of the 1064nm beam and the OPO signal and idler, sensors for the spatial and temporal overlap and a high resolution spectrometer are included. 1064nm pulses and OPO idler pulses can be independently combined with the OPO signal or blocked. The standard CARS set up utilises the 1064nm wavelength as Stokes and the signal pulse train as pump, with an energy difference from 700-5000cm-1. Other CARS set-ups use the signal and idler pulse trains (1400-10,000cm-1) for higher penetration depths, due to the red-shifted excitation wavelengths.

The specified 750mW for both1064nm and the OPO signal output, as well as 600mW for the OPO-idler, provide more than enough power for CARS and coherent Raman microscopy.

The picoEmerald offers researchers in biology, medical and other life sciences an easy-to-use light source for CARS microscopy. The next step of development, according to APE and High Q, will see microscope manufacturers integrate the picoEmerald into their confocal microscope systems, offering complete CARS imaging systems to life science users.