Characterization of microscope objective lenses from 1,400 to 1,650 nm to evaluate performance for long-wavelength nonlinear microscopy applications.

We have demonstrated a simple method for characterization of objective lens performance at longer wavelengths for 3PLSM and THG imaging. We investigated a range of air and oil-immersion objective lenses across a wavelength range of 1,400-1,650 nm using a synchronously pumped optical parametric oscillator laser source. In the first instance, we investigated the percentage light transmission across this spectral range. Second, we used a simple second harmonic autocorrelation pulse measurement technique to study the dispersion properties of these lenses at the range of input wavelengths. For the objective lenses investigated, we observed pulse broadening on the order of around 4%-7% for air immersion lenses and 9%-12% for oil immersion lenses. Even for the greater dispersion incurred by the application of the oil immersion lenses, these objectives are suitable for longer wavelength application in conjunction with a suitable light source. The same techniques could easily be applied for a larger range of objective lenses and adapted for alternative spectral windows and pulse durations.