Quantum cascade emits at multiple wavelengths

17 Jun 2002

Bell Laboratories hasdeveloped the world's first semiconductor laser to emit multiplewavelengths at 6.6, 7.3 and 8 mm in the mid-infrared. Previously onlygas and dye lasers were able to emit multiple wavelengths. The laser hasmany layers of semiconducting material to make up a quantum cascadelaser (QCL). Federico Capasso, head of theSemiconductor Physics Research Department, sees applications inenvironmental monitoring and industrial process control. The new lasingmaterial consists of AlInAs four atomic layers thick, alternating withGaInAs 18 atomic layers thick. The cascade comprises 25 such stages. "Byprecisely tailoring the layers' thickness we created a material in whichelectrons have energy levels designed to emit light at selectedwavelengths," said Capasso. The maximum output of the system so far is 1 W at 10K. At 250 K the laser emits a peak power of 100 mW atwavelengths of 6.6 and 8 mm. Increasing the injection current into thedevice generates another wavelength at 7.3 mm. Last summer, Thomson-CSFannounced the first QCL of AlGaAs layers on a GaAs substrate,demonstrating that QCLs are not bound to a specific material system. GaAs substrates, widely used in the semiconductorindustry, avoid problems of lattice-matching layers of GaInAs and AlInAsto an indium phosphide substrate.