A laser system for a spectroscopic catheter system utilizes an overmoded cavity in order to reduce mode hoping induced power fluctuations during wavelength scanning. In the preferred embodiment, a semiconductor gain medium is used to reduce cost. A fiber pigtail is used to define the laser cavity, which has a tight cavity mode spacing of less that 15 Gigahertz. A diffraction grating is used as the tuning element. A cylindrical lens is used to reduce alignment tolerances and thereby increase manufacturability.