## 1 Introduction
By contrast, SRT laser pulses in the microsecond time regime (1.7 \(\upmu\)s, 5 \(\upmu\)s) appear favorable compared to nanosecond pulses (8 ns, 200 ns) in preventing unintentional retinal damage [19; 20]. Recent clinical studies have shown promising results using SRT with a series of 15 to 30 pulses, at 1.7 \(\upmu\)s pulse duration and repetition rates of 100 Hz [12; 21; 22]. For clinical SRT application, energy dosing (i.e., absorption-corrected radiant exposure) is essential. In order to conserve photoreceptor integrity, SRT irradiation must be kept within a small treatment window close above the MBF threshold, so as to avoid insufficient or excessive exposure that would result in negligible or negative effects. This threshold varies both between patients and within retinal regions of individual patients, because of the optical transmission differences and light absorption variability at the fundus due to the localized melanosome density [5]. Furthermore, by definition, the treatment window of SRT limits induced tissue damage to the RPE within, and thus is undetectable during visual inspection of the fundus. Currently, selective RPE damage caused by microsecond laser irradiation is only detectable with biochemical methods such as fundus fluorescein angiography (FFA). This has two major drawbacks: first, it is invasive--due to the intravenously injected dye--which introduces a risk of anaphylactic shock, and second, it has a significant delay, since FFA can only be performed post-SRT-treatment (and only once per day). Hence, several approaches for real-time MBF detection and real-time laser exposure control for individual lesions (feedback-controlled irradiation) are under development. Methods such as measuring the increased reflectance at the bubble surface via backscattered light or capturing the ultrasonic emission of vaporization to detect the appearance of MBF have been successfully tested [17; 23]. An alternative dosimetry approach is to use spectral-domain optical coherence tomography (SD-OCT) simultaneously with SRT to observe MBF formation. This method was described first by [PERSON] et al., who indirectly detected tissue effects of laser pulses as signal changes in time-resolved SD-OCT A-scans (M-scans), which correspond to a change in the local reflectivity of tissue [24; 25; 26]. The detailed origin of this signal loss is still debated, but the currently favored hypothesis explains it as \"coherent fringe washouts\" resulting from the axial motion of the retina due to MBF. This coherence decorrelation is assumed to result from rapid fluctuations of the spectral phase, which are faster than the integration time of the detector and therefore larger than \(2\pi\) within the acquisition time of the interferometric measurement (typically 10 to 30 \(\upmu\)s). Successively, the time-averaged heterodyne signal--the spectral fringe pattern--diminishes, while the homodyne components--the spectral shape--are almost unaffected. This behavior indicates that neither the local nor the overall reflectivity is altered, and sensor overexposure can be ruled out as an origin of the phenomenon. Stronger changes, caused by fast variations in reflectance, i.e., as expected from larger quickly expanding or collapsing microbubbles with their high refractive index jumps between gas and fluid, also result in a loss of the homodyne signal. However, MBF also affects the homodyne spectral shape at the MBF-location, while the resulting sonic vibrations spread out laterally and axially for multiple tens of micrometers, thereby forming an enlarged volume of rapid oscillations where OCT signals get cloaked. The resulting significant sensitivity advantage of the OCT-approach compared to direct reflectance sensing potentially enables irradiation-effect estimation even at levels beneath the cell-lethality threshold. Based on this model, using signal changes of SD-OCT M-scans, [PERSON] et al. were able to precisely predict RPE lesions post-treatment in ex vivo porcine eyes [27; 28]. Furthermore, [PERSON] et al.