An assembly (14) for analyzing a sample (15) includes a detector assembly (18); a tunable laser assembly (10); and (iii) a laser controller (10F). The detector assembly (18) has a linear response range (232) with an upper bound (232A) and a lower bound (232B). The tunable laser assembly (10) is tunable over a tunable range, and includes a gain medium (10B) that generates an illumination beam (12) that is directed at the detector assembly (18). The laser controller (10F) dynamically adjusts a laser drive to the gain medium (10B) so that the illumination beam (12) has a substantially constant optical power at the detector assembly (18) while the tunable laser assembly (10) is tuned over at least a portion of the tunable range.