Devices and methods for detecting particulate matter are described herein. One device includes a laser, a reflector, an ellipsoidal reflector, and a detector, wherein the laser is configured to emit a beam, the reflector is configured to reflect the beam toward the ellipsoidal reflector, and the ellipsoidal reflector has a first focal region located on a path of the reflected beam, and a second focal region located at a surface of the detector.