Fig. 2. Multimode emitting devices.

a Plot of the current density–voltage (J–V) and light–current density (L–J) characteristics of Octonacci lasers with a length of 2.9 mm and a slit length of L = 1.9 µm for different ridge widths of W = 60 µm and W = 160 µm. The measurements were performed at a heat sink temperature of 20 K, while driving the device in pulsed mode with a pulse width of 200 ns and a pulse repetition rate of 50 kHz (i.e., with a 1% duty cycle). The dashed blue curve represents the L–J characteristic of the device with W = 160 µm measured at 78 K, under identical driving conditions. The optical power scale was corrected to take into account the 75% transmission of the cryostat polyethylene window and the radiation collection efficiency of the pyroelectric detector. b Fourier transform infrared (FTIR) emission spectrum of the device with W = 60 µm and L = 1.9 µm operated at 12 K with a 4% duty cycle, acquired with a spectral resolution of 0.125 cm⁻¹ c FTIR emission spectrum of an Octonacci laser with a ridge width of W = 160 µm and slit aperture length of L = 1.9 µm, operated at a heat sink temperature of 12 K and a 1% duty cycle. Up to 13 distinct modes are visible, with −20 dB mode suppression. d Far-field intensity pattern of an Octonacci laser with W = 60 µm and L = 1.9 µm, measured by scanning the pyroelectric detector on a spherical surface at a distance of 7 cm from the laser top plane. The laser was driven in pulsed mode (pulse frequency of 50 kHz and pulse width of 200 ns) at a heat sink temperature of 20 K and at J = 500 A/cm². The far-field angles (φ, ϑ) are defined according to the scheme in Fig. 1d. e Plot of the most intense far-field emission lobes for the device with W = 60 µm (also included in Fig. 2d) and f the brightest lobe for the laser with W = 160 µm, featuring the same slit aperture length of L = 1.9 µm. Both devices were operated under peak emission conditions with a 1% duty cycle