## 2 Materials and Methods
### Brightness Enhancement in SCL Compared to a Lamp  
Due to the diffraction-limited beam quality, SC sources can produce much higher brightness levels and therefore can be coupled into the monochromator or light delivery fibers more efficiently. Although the enhancement factor will depend on the details for a particular experimental configuration, we provide specifics for our experimental configuration of Figure 1 compared with using a lamp as the light source. As an example, for a fiber bundle of a surface area of 1 mm\({}^{2}\) and a numerical aperture of 0.3, while the etendue of the optical fiber is just 0.28 mm\({}^{2}\). When a black body emitter (emissivity of 0.4) at a 3000-K temperature is coupled into this fiber bundle, the coupled spectral density is \(\sim\)0.35 mW/nm at 900 nm. As a comparison, at the same wavelength, the SCL source used in this study provides a spectral density of \(\sim\)3 mW/nm, which corresponds to roughly an 8.9-dB higher output power than a conventional light source. Figure 3 plots the spectral density versus the wavelength for the SCL (black curve) versus the black body radiator (red curve), illustrating the higher spectral density for the SCL. This curve is over the spectral range of 750-900 nm, the wavelength ranges over which the CCO measurements are conducted. However, at longer wavelengths (e.g., the SWIR), the benefit of using the SCL becomes much higher, since the spectral density of the SCL further increases (c.f. Figure 2b).  
It should be noted that in this study, the monochromator was placed before the sample or participants to extract a higher output spectral density while preventing sample or participant discomfort or damage from high-power optical illumination. The maximum brightness allowed in clinical practice is limited by the maximum permissible energy (MPE). As an example, the MPE standards are documented in the American National Standard for Safe Use of Lasers, document number ANSI Z136.1-2014 (published by the Laser Institute of America and American National Standards Institute, Inc. (ANSI, Washington, DC, USA), ISBN 978-1-940168-01-2). We were careful to stay under this MPE, as were published works such as [27] that used lamps. However, within that limit, the SCL-based SCISCCO could achieve a much higher brightness. This is because the fiber-based super-continuum laser with a transform-limited spatial beam allowed us to couple it efficiently into a spectrometer and then into a delivery fiber, so we could deliver at a particular setting of the spectrometer  
Figure 3: Comparison of spectral density coupled into 1-mm\({}^{2}\) area fiber between 3000-K black body emitter and SC laser used in this study.  
a relatively narrow band of light limited by the MPE energy level. In comparison, when using an incoherent lamp, all of the lamp wavelengths need to be coupled to the delivery fiber to have enough reflected light to achieve a reasonable signal-to-noise ratio (SNR). In the lamp experiments, the spectrometer can be used only after the reflected light from the participant. Thus, while both designs cannot go beyond the MPE limits on the participant, the SCISCCO system with the spectrometer before the participant or sample can achieve a much higher spectral density, resulting in an improved SNR.