Ultra-low timing jitter, Ti:Al2O3 synchronisation for stimulated Raman scattering and pump-probe microscopy

Abstract

Significance: Stimulated Raman scattering and pump-probe microscopy are implementations of multiphoton microscopy that acquire high-resolution, label-free images of live samples encoded with molecular contrast. Most commercial multiphoton microscopes cannot access these techniques since they require sample illumination by two temporally synchronised ultrafast modelocked pulse trains. Here, we present a compact and robust way of synchronising an additional Ti:Sapphire laser with a conventional single beam multiphoton microscope to realise an instrument that can acquire images with enhanced molecular specificity. Aim: A passive optical synchronisation scheme for a pair of commercially available, unmodified modelocked Ti:Sapphire lasers was developed. The suitability of this synchronisation scheme for advanced biomedical microscopy was investigated. Approach: A pair of modelocked Ti:Sapphire lasers were aligned in master-slave configuration. 5% of the master laser output was used to seed the modelocking in the slave laser cavity. The timing jitter of the master and slave pulse trains was characterised using an optical autocorrelator. The synchronised output of both lasers was coupled into a laser scanning microscope and used to acquire spectral focussing stimulated Raman scattering and pump-probe microscopy images from biological and non-biological samples. Results: A timing jitter between the modelocked pulse trains of 0.74 fs was recorded. Spectral focussing stimulated Raman scattering allowed spectral discrimination of polystyrene and polymethyl methacrylate beads. Pump-probe microscopy was used to record excited state lifetime curves from haemoglobin in intact red blood cells. Conclusion: This work demonstrates a simple and robust method of upgrading single beam multiphoton microscopes with an additional ultrafast laser. The resulting dual-beam instrument can be used to acquire label-free images of sample structure and composition with high biochemical specificity.