Fig. 1. Schematic of conduction band of QCL^[12]

Fig. 2. Schematic of EC-QCL with Littrow structure

Fig. 3. Structural diagrams of EC-QCL

Fig. 4. Relationship between diffraction efficiency of blazed grating and wavelength under different incident polarized electric-field directions. (a) Grating with groove spacing of 450 line/mm; (b) grating with groove spacing of 300 line/mm

Fig. 5. Tuning characteristics of EC-QCL under different gratings. (a) Grating with groove spacing of 450 line/mm; (b) grating with groove spacing of 300 line/mm

Fig. 6. SMSR of EC-QCL underdifferent gratings. (a) Grating with groove spacing of 450 line/mm; (b) grating with groove spacing of 300 line/mm

Fig. 7. Spot images captured at different working distances using different blazed gratings

Fig. 8. Power curves of lasers under different blazed gratings