Fig. 3. Single-frequency-mode emitting devices.

a V–J and L–J characteristics of a set of 2.9-mm-long Octonacci lasers with ridge widths of W = 160 µm, W = 80 µm and W = 40 µm. The slit length ranges between L = 3.5 µm (for W = 80–160 µm) and L = 4.0 µm (for W = 40 µm). The L–J–V characteristics were measured at a heat sink temperature of 20 K in pulsed mode with a 1% duty cycle (pulsed width of 200 ns and a pulse repetition rate of 50 kHz). The dashed blue curve represents the L–J characteristic of the device with W = 80 µm, measured at 78 K, under identical driving conditions. The optical power scale was corrected to take into account the radiation collection efficiency of the pyroelectric detector and the 75% transmission of the polyethylene window of the cryostat. b FTIR emission spectra of the single-frequency-mode devices with W = 160 µm (blue), W = 80 µm (red) and W = 40 µm (green) operated at 12 K in pulsed mode with a duty cycle of 4%, measured with a resolution of 0.125 cm⁻¹ and averaging over 32 scans. c Far-field intensity patterns measured 7 cm away from the top surface of a laser with W = 160 µm and L = 3.5 µm, while keeping the heat sink temperature fixed at 15 K with a duty cycle of 1%, at J = 550 A/cm²