## 2 Materials and Methods
### Modulational Instability-Initiated SC Source
Since both self-phase modulation and the Raman effect are self-phase-matched, the processes are efficient and do not require delicate selection of the fiber properties. Additionally, the Raman effect is very efficient, and it is the dominant nonlinear mechanism for generating light in longer wavelengths (e.g., the long wavelength edge shifts outward by emitting optical phonons). Because of the very high efficiency of the Raman effect, in our experience, the SC bandwidth will fill the transparency band of the fiber as long as a sufficiently high peak power is available. Thus, the short wavelength side of the SC spectrum is created through four-wave mixing or self-phase modulation, and the short wavelength edge is usually limited by the increasing group velocity dispersion in the fiber. On the other hand, the long wavelength side of the SC is dominated by the Raman effect mechanism, and the limit on the long wavelength side is from the rising loss in the fiber at longer wavelengths. As Figure 2a illustrates, for a modulational instability-initiated SC system, the SCL is just a MOPA pump (common in most telecommunications applications) followed by several short lengths of fiber coupled together. The prototype shown in Figure 2a comprises a cascade of fibers pumped by fiber-pigtailed laser diodes and some drive and control electronics. Thus, the SC sources have the potential to be cost-effective, compact, robust, and reliable. For SC wavelengths up to about 2600 nm, fused silica fibers can be used, which are the traditional fibers used in telecommunications that can be easily spliced. Hence, for the spectrum shown in Figure 2b, only fused silica-based fibers are required, and the entire SCL has fibers spliced together with no moving parts. For the particular set-up in Figure 2a, the seed laser is a distributed feedback semiconductor laser that outputs ~1-ns pulses at an adjustable repetition rate from 100 kHz to 4 MHz. Because of the MOPA design, the SC provides scalable time-averaged output power between 0.3 W (at a 100-kHz repetition rate) and 10 W (at a 4-MHz repetition rate) with power stability at \(\pm\)0.21% while maintaining roughly the same output spectrum from 670 nm to 2500 nm (Figure 2b). At the maximum time-averaged output power of ~11 W, the wall plug efficiency for the entire laser is ~11% (i.e., the ratio of the output optical power from the SCL divided by the complete electrical power drawn from the wall for the entire unit (all of the electronics, optics, cooling, etc.)). Moreover, the SC output beam is spatially coherent, with a near-diffraction limited quality across the entire output spectral range. Since solid core, fused-silica fibers are used throughout and transmit over the entire NIR and SWIR range, all of the fibers, fiber-pigtailed components, and fiber-pigtailed laser diodes are fusion spliced in the set-up. Fans are placed above the pump lasers to provide cooling. A photograph of the SCL source (made by Omni Sciences) is shown in Figure 2a. (The SCL footprint is 10\({}^{\prime\prime}\)\(\times\) 14\({}^{\prime\prime}\)\(\times\) 2.5\({}^{\prime\prime}\), and the weight is about 11 pounds.)