3D printed high-NA ultra-thin catadioptric condenser to minimize background contribution from cross-phase modulation in stimulated Raman scattering microscopy (Conference Presentation)

Abstract

To avoid the unwanted non-resonant background contribution induced by cross-phase modulation (XPM) in Stimulated Raman Scattering (SRS) microscopy [1], the collection of forward transmitted signal is normally done with a microscope objective having a numerical aperture (NA) higher than the objective used for excitation. However, while high NA microscope objectives are usually bulky and expensive, because a complex design is needed to achieve good optical imaging performances, only a capability to collimate highly divergent beams is needed for forward detection of signal in SRS microscopy. Additionally, because high NA microscope objectives have a short working distance and are bulky, their use as forward collecting optical element is not compatible with tightly closed top-stage incubators, as used in live-cell experiments. Here we show the use of a high NA 3D printed ultra-thin optical lens, composed of micro-reflective and -refractive elements, to replace commercial high NA microscope objectives for forward collection of signal in Stimulated Raman Scattering microscopy. The lens is fabricated on a 170µm thick coverslip with direct laser writing based on Two-Photon Lithography with a commercial system (Nanoscribe) and using the proprietary IP-S photoresist. It has a thickness of 300 µm and a diameter of 1 cm. Thanks to its compactness, this optical element can easily fit inside top-stage microscope incubators. The resulting NA of this catadioptric condenser lens is 1.2 when working in water immersion. We show the complete removal of the non-resonant XPM contribution from SRS spectra of incubated cells. [1] Ji-Xin Cheng, Xiaoliang Sunney Xie, Coherent Raman scattering microscopy, CRC press, 2016.