A research group at the University of Konstanz in Germany has generated infrared light with 8-kHz linewidth from the OS 4000 optical parametric oscillator (OPO) from Linos Photonics GbmH of Planegg, Germany. The university team says that such narrow-linewidth tunable output will The team performed beat measurements on the OS 4000 by locking it with a CH4-stabilized HeNe laser at 3.39 µm. The OPO has a free-running linewidth of 90 kHz, but it displayed a linewidth of 23 kHz at medium feedback and 8 kHz at high feedback when locked with the other laser.