Abstract Single frequency laser oscillation is realized by including within the laser cavity a resonant etalon, tuned to the desired laser frequency. This has the effect of suppressing all other modes while permitting the laser to oscillate at the desired single frequency. In addition, the etalon tuning is frequency modulated about the desired frequency, producing an amplitude modulation of the laser signal. The amplitude modulation thus produced is sensed by a phase detector which generates an error signal whenever the laser frequency tends to deviate from the mean, etalon frequency. The error signal is used, in turn, to retune the laser cavity. It is an advantage of the present arrangement that spurious frequency modulation of the laser frequency, introduced by the stabilization system, is substantially less than that produced by comparable prior art stabilization circuits. Furthermore, such modulation can be conveniently reduced, or eliminated, by the addition of a dummy etalon driven in antiphase to the active etalon.
A single frequency laser comprising: an active laser medium disposed within a resonant cavity supportive of oscillations at a plurality of different frequencies; a resonant etalon, tuned to one of said frequencies, located within said cavity for suppressing oscillations at all frequencies other than said one frequency; a signal source, coupled to said etalon, for amplitude modulating said oscillations by varying the resonant frequency of said etalon over a band of frequencies about said one frequency; error detecting means coupled to the output of said laser for generating an error correcting signal whenever said laser frequency differs from said one frequency; and means responsive to said error correcting signal for adjusting the optical length of said cavity so that it remains resonant at Said one frequency.
Claim 2
Dependent Claim
126 words
A single frequency laser comprising: an active laser medium disposed within a resonant cavity supportive of oscillations at a plurality of different frequencies; a resonant etalon, tuned to one of said frequencies, located within said cavity for suppressing oscillations at all frequencies other than said one frequency; a signal source, coupled to said etalon, for amplitude modulating said oscillations by varying the resonant frequency of said etalon over a band of frequencies about said one frequency; error detecting means coupled to the output of said laser for generating an error correcting signal whenever said laser frequency differs from said one frequency; and means responsive to said error correcting signal for adjusting the optical length of said cavity so that it remains resonant at Said one frequency.
Claim 3
Dependent Claim
62 words
The laser according to claim 1 wherein said error detecting means comprises: an amplitude detector for detecting the amplitude modulation produced by varying the resonant frequency of said etalon; and means for coupling said amplitude detector to a phase detector and means for coupling a reference signal from said signal source to said phase detector, wherein said error correcting signal is generated.
Claim 4
Dependent Claim
36 words
The laser according to claim 1 wherein; said cavity comprises a pair of spaced mirrors; one of said mirrors is mounted on a piezoelectric crystal; and wherein said error correcting signal is impressed upon said crystal.
Claim 5
Dependent Claim
48 words
The laser according to claim 1 including, in addition; a second etalon disposed within said resonant cavity; said etalon having a band-pass characteristic that is uniform over said band of frequencies; and means for coupling said signal source to said second etalon in antiphase to said resonant etalon.