[en] A pulsed argon discharge inside a cw-laser cavity is used to modulate the cw-laser output via the transient gain/loss at various lasing wavelengths. Under short-pulse excitation (approximately 0.6 μs), gain is found at four Ar(II) lasing lines, but losses are observed at 4880 and 5017 A. A similar diagnostic device with broad-band capabilities and based on an ion-laser-pumped dye laser is proposed. (U.S.)