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Laser action by tuning the oscillator strength

Abstract

The threshold condition for laser action is usually achieved when the population difference between the initial and final energy levels of the laser transition reaches a critical value, determined by the equality between optical gain and losses. But the threshold condition can also be achieved by increasing the oscillator strength of the laser transition itself, while the population difference is held constant. This forms the basis of a new class of semiconductor lasers, a notable feature of which is broad wavelength tunability (on application of an electric field) in the technologically important mid-infrared region of the spectrum.

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Figure 1: Schematic energy band diagram of two periods of the new laser for different applied electric fields F: a, F. = 0; b, F ≈ 50kVcm−1;
Figure 2: Schematics of the Al0. 48In0.52As/Ga0.47In0.53As laser heterostructure D-2190. The thicknesses of the layers are given in nm and the doping level is given incm−3.
Figure 3: Intersubband electroluminescence spectra of sample D-2146 associated with the optical transition from the ground state m = 1 to 1′ (see Fig. 1c) for increasing current densities, shown in key in units of kAcm−2; solid line, 6.5kAcm−2; short-dashed line, 1.6kAcm−2; long-dashed line, 0.1kAcm−2.
Figure 4: Applied bias and measured continuous-wave optical power from a single facet as a function of injected current for a representative. laser of wafer D-2190 at various temperatures.
Figure 5: Tunable operation of the laser D-2190.
Figure 6: Two-wavelength operation of sample D-2197.

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Acknowledgements

We thank S. N. G. Chu for transmission electron microscopy work on some of the structures, and C. Gmachl for discussions.

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Correspondence to Federico Capasso.

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Faist, J., Capasso, F., Sirtori, C. et al. Laser action by tuning the oscillator strength. Nature 387, 777–782 (1997). https://doi.org/10.1038/42872

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