A laser cavity comprising a gain medium and first and second end mirrors, wherein the laser cavity further comprises a birefringent material and a mirror arranged to fold light propagating within the laser cavity through a predetermined angle, wherein the predetermined angle is selected such that the reflectivity of the fold mirror is polarisation dependent, and the birefringence of the birefringent material co-operates with the polarisation dependent reflectivity of the fold mirror to form a Lyott filter which suppresses oscillation of unwanted laser modes. The invention allows the construction of a low loss, high finesse laser cavity with longitudinal mode control. The need for introduction of an extra polarisation selection element to form a Lyott filter is removed.
A low-noise micro-chip laser includes a diode pump, a gain medium, a nonlinear crystal, and a birefringent material. The gain medium can receive the energy from the diode pump and generate a laser beam at a fundamental wavelength. The nonlinear crystal can generate a frequency-doubled laser beam in response to the laser beam at the fundamental wavelength. To reduce noise in the frequency-doubled laser beam, the birefringent material and the nonlinear crystal in combination are designed to function as a quarter wave plate at the fundamental wavelength.
