(a) Emission spectra of the dye Atto 590 under illumination with laser light at 589 nm, filtered solely with a hot (200°C) atomic vapor cell. Purple: Same spectrum, filtered with the commercial long-pass filter. The integral enhancement between atomic and the commercial filter is 15.5%. LP-filter = long-pass filter. (b) Single step bleaching of individual molecules proves the single emitter nature. (c) Transmission curves of the filter and different atomic vapor cells measured with a UV-VIS spectrometer (Lambda 16, PerkinElmer). (d) Calculated optical density of the filter (100 mm optical length) against temperature.