Supplemental Material

The Supplemental Information includes: • VMI images of two hyperfine states split by 6.9 MHz and accompanying discussion of methodology for velocity calibration of the detected images. • A labeled hyperfine spectrum of the (v = 1, J′ = 1.5) ←(v = 0, J′′ = 0.5) ro-vibrational transition of nitric oxide. • Example power spectral density graph of the error signal for a locked and free-running QCL. This is accompanied by associated data on determination of locked laser linewidth. • Another example of imaged velocity width and ions counts as a function of intensity, but for the lower e doublet F′ = 5/2 ← F′′ = 3/2 transition. In this case, the imaged velocity width is at the locking limit over the full intensity range and does not increase.