Ruby also absorbs some of the light at its lasing wavelength. Spontaneous emission below the lasing threshold produces similar properties to an LED. They are related to doped fiber amplifiers, which provide light amplification without lasing. Instead the lasing wavelength is changed. It is closely related to Raman spectroscopy and lasing processes. Carbon monoxide has also been used as a lasing medium in high-powered infrared lasers. A ruby laser is lasing at 694.3 nanometers, in a deep red color. Ruby lasers have declined in use with the discovery of better lasing media. The pump power must be higher than the lasing threshold of the laser. Liquid dyes have an extremely high lasing threshold. Typically arcing occurs "after" lasing in nitrogen. Above the threshold, the laser is said to be "lasing". With VCSOAs, reduced feedback is necessary to prevent the device from reaching lasing threshold. These originate in the Weigelt Blobs and are caused by a low-gain lasing effect. It achieved first lasing in April 2009.