US Patent 9512460 Method of studying a cryogenic sample in an optical microscope

The present invention relates to a method of studying a sample using an optical microscope, comprising providing the sample in a sample holder with means to maintain the sample at a temperature below 273 K; providing a microscope objective lens, in a thermally insulating jacket, having an extremal lens element proximal to the sample holder; bringing the lens into a focus position proximal to the sample, which separates the extremal lens element and sample by an intervening space, providing a transparent window in said intervening space, with a gap between the window and the extremal lens element; providing a flow of substantially dry gas in said gap; and tailoring the geometry and velocity of said flow so that, at least in said gap, the flow is non-laminar; and does not excite substantial acoustic vibration in a structure proximal the gap.