A novel superlattice quantum cascade (SLQC) laser has undoped SL active regions, with the dopant concentration in the injector region being selected, such that, under an appropriate electrical bias, the SL active region is substantially electric field free. The absence of dopant atoms in the SL active region results in reduced carrier scattering and reduced optical losses, with consequent low threshold current and/or room temperature operation. The novel laser emits in the mid-IR spectral region and can be advantageously used in measurement or monitoring systems, e.g., in pollution monitoring systems.