Spcm aqrh 16

The samples were measured in a liquid helium flow cryostat (Janis, SVT‐200‐5) that can reach a working temperature of 1.3 K. With an objective (0.85 NA, Edmund Optics) immersed in liquid helium, the cryostat forms part of a home‐built confocal microscope. A Ti:sapphire laser (M‐squared SolsTiS) in combination with a frequency‐doubling module (M‐squared ECD‐X) was used as a narrow bandwidth (<1 MHz) tunable excitation source, operating in the 440–460 nm range. The output wavelength of the laser was measured continuously with a wavemeter (High Finesse WS6‐200), with resolution of a few MHz. A dichroic mirror (Semrock, FF458‐Di02‐25x36) was used to separate fluorescence from the excitation light and further filtering was done by a long‐pass filter (Chroma, ET460lp). The laser beam was scanned over the sample by a scanning mirror (Newport, FSM‐300‐01) and fluorescence was detected by an avalanche photodiode (Excelitas, SPCM‐AQRH‐16). Fluorescence spectra were recorded with a Horiba iHR320 spectrometer coupled to a liquid‐nitrogen‐cooled Symphony II CCD detector. The excitation intensity was measured with a power meter (Newport 1830‐C), before the laser beam entered the cryostat.