Fig. 2

Virus lasers. a Threshold behaviour in R1 for 146 nmol mL⁻¹ fluorescein (F1, dark orange) and for virus-lasing probes (V1) diluted from 413 pmol mL⁻¹ (purple) to 351 pmol mL⁻¹ (dark blue, equivalent to 135 nmol mL⁻¹ fluorescein), 270 pmol mL⁻¹ (green), 219 pmol mL⁻¹ (light purple), 185 pmol mL⁻¹ (cyan), 140 pmol mL⁻¹ (light green), 103 pmol mL⁻¹ (blue), and 72 pmol mL⁻¹ (grey). The fitted curves represent a global fit of all of the sets of threshold data to a theoretical model (Supplementary Fig. 5; Methods). Errors in the concentration described in Methods. b Emission spectra of V1 at 413 pmol mL⁻¹ as pumping increased from 5.5 × 10¹⁴ photons pulse⁻¹ ± 10.1% (cyan) to 9.1 × 10¹⁴ photons pulse⁻¹ ± 6.6% (dark blue). Inset, bathochromic shift in the spectrum of V1 (purple, pumping of 1.5 × 10¹⁵ photons pulse⁻¹ ± 10.9%) relative to 72 nmol mL⁻¹ fluorescein (orange, 1.7 × 10¹⁶ photons pulse⁻¹ ± 11.4%). Curves are fits to the sum of two Gaussian peak functions. The intensity was not calibrated but was proportional to the number of photons entering the spectrometer (see Methods). Source data are provided as a Source Data file