Quantum cascade laser device

A quantum cascade laser device comprising a hollow housing having an emission window for emitting laser light to outside;

• the housing having therewithin:
• a heatsink;
• a submount secured to the heatsink;
• a quantum cascade laser element secured to the submount;
• and
• a cover member opposing the submount so as to be located between one emission end face of the quantum cascade laser element and the emission window and having a light absorption property for the laser light emitted from the one emission end face and another emission end face of the quantum cascade laser element;
• the one emission end face of the quantum cascade laser element and a surface opposing the cover member in the submount being flush with each other;
• the cover member having an opening, located at a position opposing the one emission end face, for passing therethrough the laser light toward the emission window;
• the opening having a tapered first opening part increasing a diameter from the one emission end face side to the emission window side and a second opening part formed with a fixed diameter not smaller than the smallest diameter of the first opening part on the one emission end tee side of the first opening part.