Multiple Output Repetitively Pulsed Laser

Abstract

A continuously pumped, mode-locked laser is disclosed, which includes a cavity dumper that can remove a constant fraction of the light from the cavity at every 1/f period of time, independent of the time at which the first pulse in a train is initiated. The cavity dumper includes a modulator and two output arms, denoted as a primary output arm and a secondary output arm. When a user desires a train of pulses, the pulses are directed to the primary output arm. Between trains of pulses, when no pulse is desired by the user, the pulses are directed to the secondary output arm, which terminates in an absorber or at a secondary optical system. In this manner, the energy contained in each output pulse is essentially constant, from pulse-to-pulse and from train-to-train. This may overcome the disadvantage of many lasers that have a single output arm, in which the first pulse in a train may have an energy that depends on the length of the inactive period that immediately precedes the train.

1 . A method of generating a laser output, comprising:
 amplifying a first laser pulse within a cavity of a laser to establish a second laser pulse propagating along a path within the cavity in a first direction;   directing a first fraction of the second laser pulse into a first output arm, wherein a second fraction of the second laser pulse continues to propagate along the path in the first direction;   amplifying the second fraction of the second laser pulse within the cavity to establish a third laser pulse propagating along the path within the cavity in a second direction opposite the first direction;   directing a third fraction of the third laser pulse into a second output arm, wherein a fourth fraction of the third laser pulse continues to propagate along the path in the second direction;   amplifying the fourth fraction of the third laser pulse within the cavity to establish a fourth laser pulse within the cavity; and   extracting the third fraction of the third laser pulse from the second output arm to provide the laser output.   
     
     
         2 . The method of  claim 1 , wherein the laser output include multiple pulses from the second output arm. 
     
     
         3 . The method of  claim 1 , wherein each amplifying step comprises repeating for a predetermined number of cavity round-trips:
 propagating along the path within the cavity in the first direction;   transmitting through a continuously pumped gain medium in the first direction;   transmitting through a cavity dumper in the first direction;   propagating along the path within the cavity in the second direction;   transmitting through the cavity dumper in the second direction; and   transmitting through the continuously pumped gain medium in the second direction.   
     
     
         4 . The method of  claim 1 ,
 wherein a cavity dumper directs the first fraction of the second laser pulse into the first output arm; and   wherein the cavity dumper directs the third fraction of the third laser pulse into the second output arm.   
     
     
         5 . The method of  claim 1 , further comprising:
 rotating the plane of polarization of the second laser pulse;   directing the second laser pulse onto a first inclined polarizer, the first inclined polarizer reflecting the first fraction of the second laser pulse and transmitting the second fraction of the second laser pulse;   rotating the plane of polarization of the third laser pulse; and   directing the third laser pulse onto a second inclined polarizer, the second inclined polarizer reflecting the third fraction of the third laser pulse and transmitting the fourth fraction of the third laser pulse.   
     
     
         6 . The method of  claim 5 ,
 wherein an electro-optic modulator rotates the planes of polarization of both the second and third laser pulses.   
     
     
         7 . The method of  claim 6 ,
 further comprising providing the electro-optic modulator with a driving signal timed to coincide with passage of the laser pulses through the electro-optic modulator.   
     
     
         8 . The method of  claim 6 , wherein the first and second inclined polarizers reflect s-polarized light, transmit p-polarized light, are essentially parallel, and are disposed on opposite sides of the electro-optic modulator in the cavity. 
     
     
         9 . The method of  claim 1 , further comprising:
 amplifying the fourth laser pulse within the cavity of the laser to establish a fifth laser pulse propagating along the path in the first direction;   directing a fifth fraction of the fifth laser pulse into the first output arm, wherein a sixth fraction of the fifth laser pulse continues to propagate along the path in the first direction;   amplifying the sixth fraction of the fifth laser pulse within the cavity to establish a sixth laser pulse propagating along the path within the cavity in the second direction;   directing a seventh fraction of the sixth laser pulse into the second output arm, wherein an eighth fraction of the sixth laser pulse continues to propagate along the path in the second direction;   amplifying the eighth fraction of the sixth laser pulse within the cavity to establish a seventh laser pulse within the cavity; and   extracting the seventh fraction of the sixth laser pulse from the second output arm to provide the laser output.   
     
     
         10 . A method of generating output pulses from a laser having a cavity bounded by a first mirror and a second mirror and containing a circulating intracavity pulse, comprising:
 repeating for a predetermined number of cavity round-trips the sequence of:
 reflecting the intracavity pulse from the first mirror; 
 retaining the intracavity pulse in the cavity with the cavity dumper; 
 reflecting the intracavity pulse from the second mirror; and 
 retaining the intracavity pulse in the cavity with the cavity dumper; 
   reflecting the intracavity pulse from the first mirror;   directing a fraction of the intracavity pulse into a first output arm with a cavity dumper to form a first output pulse;   retaining a fraction of the intracavity pulse in the cavity;   reflecting the intracavity pulse from the second mirror;   retaining the intracavity pulse in the cavity with the cavity dumper;   repeating for the predetermined number of cavity round-trips the sequence of:
 reflecting the intracavity pulse from the first mirror; 
 retaining the intracavity pulse in the cavity with the cavity dumper; 
 reflecting the intracavity pulse from the second mirror; and 
 retaining the intracavity pulse in the cavity with the cavity dumper; 
   reflecting the intracavity pulse from the first mirror;   retaining the intracavity pulse in the cavity with the cavity dumper;   reflecting the intracavity pulse from the second mirror;   directing a fraction of the intracavity pulse into a second output arm with a cavity dumper to form a second output pulse; and   retaining a fraction of the intracavity pulse in the cavity.   
     
     
         11 . The method of  claim 10 , further comprising amplifying the intracavity pulse with a continuously pumped gain medium. 
     
     
         12 . The method of  claim 10 , further comprising shortening the intracavity pulse with a mode locker. 
     
     
         13 . The method of  claim 10 , further comprising:
 transmitting a fraction of the intracavity pulse through the first mirror to form transmitted light;   detecting the transmitted light with a photodetector to form a synchronization signal;   generating a modulator driving signal synchronized to the synchronization signal; and   providing the modulator driving signal to the cavity dumper.   
     
     
         14 . A method of generating output pulses from a laser having a cavity bounded by a first mirror and a second mirror and containing a circulating intracavity pulse, comprising:
 repeating for a predetermined number of cavity round-trips the sequence of:
 reflecting the intracavity pulse from the first mirror; 
 retaining the intracavity pulse in the cavity with a cavity dumper; 
 reflecting the intracavity pulse from the second mirror; and 
 retaining the intracavity pulse in the cavity with the cavity dumper; 
   reflecting the intracavity pulse from the first mirror;   directing the intracavity pulse to the cavity dumper, the intracavity pulse having a total power at incidence upon the cavity dumper;   directing with the cavity dumper a first output percentage of the intracavity pulse into a first output arm to form a first output laser pulse;   retaining a first retention percentage of the intracavity pulse in the cavity;   reflecting the intracavity pulse from the second mirror;   directing with the cavity dumper a second output percentage of the intracavity pulse into a second output arm to form a second output laser pulse; and   retaining a second retention percentage of the intracavity pulse in the cavity;   wherein the first output percentage is a desired output divided by the total power;   wherein the first retention percentage is 100% minus the first output percentage;   wherein the second output percentage is a cavity dumping ratio minus the first output percentage; and   wherein the second retention percentage is 100% minus the cavity dumping ratio.   
     
     
         15 . The method of  claim 14 , wherein the first output percentage is zero and the second output percentage is the cavity dumping ratio. 
     
     
         16 . The method of  claim 14 , wherein the first output percentage is the cavity dumping ratio and the second output percentage is zero. 
     
     
         17 . A laser, comprising:
 a cavity for containing intracavity light in a first direction and a second direction opposite the first direction;   a cavity dumper disposed in the cavity for selectively diverting intracavity light into either or neither of a first output arm or a second output arm, comprising a first polarizer having a first pass axis, a second polarizer having a second pass axis, and a modulator disposed in the laser cavity between the first and second polarizers; and   a modulator controller for selectively rotating the polarization of intracavity light traveling in the first direction away from the first pass axis so that intracavity light traveling in the first direction reflects off the first polarizer to form the first output arm, and for selectively rotating the polarization of intracavity light traveling in the second direction away from the second pass axis so that intracavity light traveling in the second direction reflects off the second polarizer to form the second output arm.   
     
     
         18 . The laser of  claim 17 , further comprising:
 a mode locker disposed in the cavity for forming a pulse that circulates in the cavity and alternates between first and second directions;   a continuously pumped gain medium disposed in the cavity for amplifying the circulating pulse; and   a photodiode for monitoring the position of the pulse in the cavity, and for generating a synchronization signal.   
     
     
         19 . The laser of  claim 18 , wherein the modulator controller receives the synchronization signal and drives the modulator with a time-synchronized driving signal that selectively rotates the plane of polarization when the pulse passes through the modulator; 
     
     
         20 . The laser of  claim 19 ,
 wherein the time-synchronized driving signal includes first and second signal pulses;   wherein the first signal pulses start at a first time with respect to the synchronization signal;   wherein the second signal pulses start at a second time with respect to the synchronization signal; and   wherein the difference between first and second times corresponds to a round-trip time between the modulator and a cavity mirror.