Abstract: A birefringent filter ("BRF") unit, for use in the cavity of a tunable pulsed laser generating ultrashort pulses, including means for suppressing satellite pulses resulting from surface reflections. In one preferred embodiment, the inventive BRF has substantially parallel front and back surfaces, and is cut so that its optical axis is not parallel to its front surface. For example, the inventive BRF may be a quartz crystal having a thickness of 3 mm, with its optical axis oriented at an angle substantially equal to 50 degrees from the plane of its front surface. In a second preferred embodiment, the inventive BRF includes a relatively thick, non-birefringent component coupled with index matching material to a relatively thin birefringent component. In a third preferred embodiment, the inventive BRF includes a pair of thick birefringent components designed so that the ordinary ray of the first component becomes the extraordinary ray of the second component.

Abstract: Mode-locked pulsed output is induced in a laser by introducing a varying frequency dependent loss in the cavity. The varying, frequency dependent loss allows a large number of longitudinal modes to oscillate. In one of the preferred embodiments of the subject invention, the varying frequency dependent loss is generated by reciprocating one of the mirrors of the resonator. In this embodiment, the laser has a resonator with a primary light path defined by first and second end mirrors. A gain medium is located between the end mirrors. A beam splitter is provided for redirecting the light into a secondary light path. A third mirror functions to feed back the light into the primary light path. Pulse formation is induced by varying the path length of one of the two paths by reciprocating an end mirror. Moving the mirror creates varying interference effects when the light energy is recombined at the beam splitter. The mirror is reciprocated relatively slowly, yet ultra-short pulses are generated.

Abstract: A birefringent filter ("BRF") unit, for use in the cavity of a tunable pulsed laser generating ultrashort pulses, including means for suppressing satellite pulses resulting from surface reflections. In one preferred embodiment, the inventive BRF has substantially parallel front and back surfaces, and is cut so that its optical axis is not parallel to its front surface. For example, the inventive BRF may be a quartz crystal having a thickness of 3 mm, with its optical axis oriented at an angle substantially equal to 50 degrees from the plane of its front surface. In a second preferred embodiment, the inventive BRF includes a relatively thick, non-birefringent component coupled with index matching material to a relatively thin birefringent component. In a third preferred embodiment, the inventive BRF includes a pair of thick birefringent components designed so that the ordinary ray of the first component becomes the extraordinary ray of the second component.

Abstract: Herein is disclosed a method of and apparatus for measuring optical frequency variations wherein linearly-polarized incident light generated by a tunable laser or the like is delivered to a passive resonant cavity incorporating a linear polarizer such as a Brewster plate so that the reflected light acquires a frequency-dependent elliptical polarization which can be detected by a simple polarization analyzer providing a signal correlated with the frequency variation of the laser. Such signal can be utilized as a feedback error signal to stabilize the laser frequency, or to adjust the cavity resonance. If the cavity is tunable, tuning thereof will in turn provide a precision method for tuning of the laser itself.