Acousto-optical laser isolator

An acousto-optical isolator for isolating, from a laser beam having a predetermined frequency and propagating forwardly along a predefined path, any unwanted, backwardly propagating laser beam having a like frequency, the isolator comprising:

• frequency shift means, disposed to receive a laser beam propagating along a first portion of the path for shifting the frequency thereof by a first amount, and disposed to receive a laser beam propagating along a second portion of the predefined path for shifting the frequency thereof by a second amount, the second amount being the converse of the first;
• reflecting means, operative to reflect a forwardly propagating laser beam from a first portion of the path onto a second portion thereof and to reflect a backwardly propagating laser beam from the second portion of the path onto the first portion thereof, whereby the frequency of a forwardly propagating beam is shifted by the first amount as the beam propagates through the shift means along the first portion of the path and then is shifted back to the predetermined frequency as the beam propagates through the shift means along the second portion of the path after having been reflected from the first portion onto the second portion by the reflecting means, and the frequency of any unwanted, backwardly propagating beam is shifted by the second amount as the beam propagates through the shift means along the second portion of the path and then is shifted back to the predetermined frequency as the beam propagates through the shift means along the first portion of the path after having been reflected from the second portion onto the first portion by the reflecting means;
• and
• attenuation mean, disposed to receive any beam that is being reflected from either portion of the path onto the other and to attenuate any beam having a frequency equal to the predetermined frequency shifted by the second amount whereby any unwanted, backwardly propagating beam is attenuated and is thereby isolated from the desired beam.

An isolating ring laser oscillator comprising:

• amplifier means, having an input for receiving a forwardly propagating laser beam of predetermined frequency, for amplifying the received laser beam;
• a plurality of reflector means, disposed to receive the amplified laser beam from the amplifier means and to reflect the beam around the amplifier and back into the input for further amplification;
• and
• an acousto-optical isolator for isolating from the forwardly propagating amplified laser beam any unwanted, backwardly propagating beam of like frequency, the isolator comprising:
• first frequency shift means, disposed to receive the amplified laser beam and to shift the frequency thereof by a first amount;
• second frequency shift means, disposed forwardly of the first shift means to receive the amplified laser beam from the first shift means and to shift the frequency thereof by a second amount, the second amount being the converse of the first amount, whereby the frequency of the amplified laser beam is shifted back to the predetermined frequency by the second shift means, and whereby the frequency of any backwardly propagating beam is shifted by the second amount as it propagates through the second shift means and then is shifted back to the predetermined frequency as it propagates through the first shift means;
• and
• attenuation means, disposed between the first and second shift means to receive any beam propagating therebetween and to attenuate any beam having a frequency equal to the predetermined frequency shifted by the second amount whereby any backwardly propagating beam is attenuated and is thereby isolated from the amplified laser beam.

A frequency-stabilized isolating ring laser oscillator comprising:

• amplifier means, having an input for receiving a forwardly propagating laser beam of predetermined frequency to amplify the received beam;
• a plurality of reflector means, disposed to receive the amplified laser beam from the amplifier means and to reflect the beam along a predefined primary path around the amplifier and back into the input for further amplification;
• an acousto-optical isolator for deriving from the forwardly propagating amplified laser beam a frequency error signal, and for isolating from the beam any unwanted, backwardly propagating beam of like frequency, the isolator comprising:
• beam splitting means, disposed to receive the amplified laser beam and to deflect a portion thereof onto a secondary path;
• first frequency shift means, disposed across the primary and secondary paths, for shifting the frequency of a laser beam propagating along the primary path by a first amount and to shift the frequency of a laser beam propagating along the secondary path by a second amount, the second amount being the converse of the first amount;
• second frequency shift means, disposed forwardly of the first shift means along the primary path to receive the amplified laser beam and to shift the frequency thereof by said second amount, whereby the frequency of the beam is shifted by the first amount as the beam propagates along the primary path through the first shift means and then is shifted back to the predetermined frequency as the beam propagates through the second shift means and the frequency of any unwanted, backwardly propagating beam is shifted by the second amount as the beam propagates through the second shift means and then is shifted back to the predetermined frequency as the beam propagates through the first shift means;
• attenuation means, disposed between the shift means to receive any beam propagating therebetween and to attenuate any beam having a frequency equal to the predetermined frequency shifted by the second amount, whereby any backwardly propagating beam is attenuated and is thereby isolated and whereby a beam propagating along the secondary path is also attenuated;
• and
• detector means, disposed across the secondary path between the attenuation means and the second frequency shift means to receive the attenuated secondary beam and responsive thereto to provide a frequency error signal;
• and
• means responsive to the frequency error signal to correct the frequency of the oscillator.

A noise-isolating laser radar comprising:

• transmitter means to provide a pulsed laser beam having a predetermined frequency;
• means to direct the pulsed laser beam toward a target whereby a portion of the beam is reflected back from the target along a reflection path;
• a switching isolator to isolate the reflected beam from any unwanted noise energy having a like frequency and propagating along the reflection path, the isolator comprising:
• first frequency shift means, disposed to receive optical energy propagating along the reflection path, responsive to a control signal to shift the frequency of the received energy selectively by a first amount or a second amount, the second amount being the converse of the first;
• second frequency shift means, disposed forwardly of the first shift means to receive optical energy propagating along the reflection path, responsive to said control signal to shift the frequency of the received energy back to the predetermined frequency;
• and
• attenuation means, disposed between the shift means to receive any optical energy propagating therebetween and to attenuate any such energy having a frequency equal to the predetermined frequency shifted by the second amount whereby such energy is attenuated and is thereby isolated;
• control signal means, responsive to the transmitter means to generate the control signal, the control signal selective the first amount in the first shift means and the second amount in the second shift means when the reflected laser beam is present and reversing said selections when the reflected laser beam is not present;
• and
• detector means, to provide a signal indicative of said reflected laser beam.