In part, the invention relates to frequency-domain optical coherence tomography system. The system includes a tunable laser comprising a laser output for transmitting laser light and a laser cavity having a length L, a gain element disposed within the laser cavity; a tunable wavelength selective element disposed within the laser cavity; a reference reflector disposed outside of the laser cavity; an interferometer in optical communication with the laser output and the reference reflector, wherein the interferometer is configured to transmit a portion of the laser light to a sample and combine light scattered from the sample with light scattered from the reference reflector; and a detector in optical communication with the interferometer that receives the combination of light scattered from the sample and the light scattered from the reference reflector and transforms the combination of light into an electronic signal comprising measurement data with respect to the sample.