Very high power pulsed fiber laser

Abstract

A pulsed fiber laser including fiber preamplifier and power amplifier stages is disclosed. A fiber preamplifier includes first and second preamplifier stages that receive and amplify a seed pulse. A filter isolator placed between the preamplifier stages suppresses noise from the first preamplifier stage. An acoustic optical modulator located in the second preamplifier stage eliminates unwanted wavelengths from the amplified seed pulse received from the first preamplifier stage. The pulsed fiber laser is rugged and lightweight.

1 . A fiber laser amplifier comprising:
 a seed laser configured to produce a seed pulse at a pulse repetition rate of about 10 Hz to about 10 KHz;   a fiber preamplifier configured to receive and amplify the seed pulse, the fiber preamplifier having a first core diameter;   a fiber power amplifier comprising a low numerical aperture, coiled clad fiber, having a core diameter larger than the first core diameter; and   a coupler configured to couple the fiber preamplifier to the fiber power amplifier.   
     
     
         2 . The fiber laser amplifier according to  claim 1 , wherein the low numerical aperture is between about 0.06 and 0.08. 
     
     
         3 . The fiber laser amplifier according to  claim 1 , further comprising a tapered fiber bundle connected to a cladding of the fiber power amplifier configured to direct pump energy into the cladding. 
     
     
         4 . The fiber laser amplifier according to  claim 1 , further comprising:
 a first pumping device configured to pump the fiber preamplifier,   a second pumping device configured to pump the fiber power amplifier, and   a synchronizing device configured to synchronize the seed pulse with the pumping devices.   
     
     
         5 . The fiber laser amplifier according to  claim 1 , further comprising one or more additional power amplifiers, wherein the core diameter of each additional power amplifier increases with each subsequent power amplifier stage. 
     
     
         6 . A pulsed fiber laser comprising:
 a seed laser configured to produce a seed pulse at a pulse repetition rate of about 10 Hz to about 10 KHz;   a first amplifier configured to receive and amplify the seed pulse, the first amplifier having a first core diameter;   a second amplifier comprising coiled clad fiber having a second core diameter, the second core diameter being larger than the first core diameter; and   a coupler configured to couple the first and second amplifiers;   wherein core diameters of the second amplifier and subsequent amplifiers increase with each subsequent amplifier stage.   
     
     
         7 . The pulsed fiber laser of  claim 6 , further comprising a tapered fiber bundle connected to a cladding of the second amplifier configured to direct pump energy into the cladding. 
     
     
         8 . The pulsed fiber laser of  claim 6 , further comprising:
 a first pumping device configured to pump the first amplifier,   a second pumping device configured to pump the second amplifier, and   a synchronizing device configured to synchronize the seed pulse with the pumping devices.   
     
     
         9 . The pulsed fiber laser of  claim 6 , wherein the fiber of the second amplifier comprises a low numerical aperture. 
     
     
         10 . A fiber preamplifier, comprising:
 a first fiber preamplifier stage configured to receive and amplify a seed pulse produced by a seed laser at a pulse repetition rate of about 10 Hz to about 10 KHz, the first fiber preamplifier stage comprising a first core diameter;   a second fiber preamplifier stage configured to receive the amplified seed pulse, the second fiber preamplifier stage comprising a second core diameter and an acoustic optical modulator (AOM); and   a filter isolator located between the first fiber preamplifier stage and the second fiber preamplifier stage, the filter isolator configured to suppress noise from the first fiber preamplifier stage;   wherein the second core diameter is larger than the first core diameter.   
     
     
         11 . The fiber preamplifier of  claim 10 , further comprising:
 a first pumping device configured to pump the first fiber preamplifier stage;   a second pumping device configured to pump the second fiber preamplifier stage; and   a synchronizing device configured to synchronize the seed pulse with the pumping devices.   
     
     
         12 . The fiber preamplifier of  claim 10 , wherein the first fiber preamplifier stage further comprises:
 an optical isolator configured to receive and optically isolate the seed pulse;   a coiled, single-mode fiber amplifier having the first core diameter and configured to receive the optically isolated seed pulse;   a first wavefront division multiplexer configured to couple the optically isolated seed pulse and pump light from a first pumping device to the coiled, single-mode fiber amplifier in a first direction; and   a second wavefront division multiplexer configured to couple pump light from a second pumping device to the coiled, single-mode fiber amplifier in a second direction.   
     
     
         13 . The fiber preamplifier of  claim 12 , wherein the second direction is opposite the first direction. 
     
     
         14 . The fiber preamplifier of  claim 10 , wherein the filter isolator further comprises a narrow band filter configured to suppress amplified spontaneous emission noise. 
     
     
         15 . The fiber preamplifier of  claim 10 , wherein the AOM is a time gated filter and is configured to receive the amplified seed pulse and eliminate unwanted wavelengths from the amplified seed pulse. 
     
     
         16 . The fiber preamplifier of  claim 15 , wherein the AOM is tuned to a pulse frequency of the seed laser. 
     
     
         17 . The fiber preamplifier of  claim 10 , further comprising:
 a coiled, clad-pumped fiber amplifier having the second core diameter; and   a mode field adapter located between the AOM and the coiled, clad-pumped fiber amplifier, the mode field adapter configured to match modes of the amplified seed pulse to the coiled, clad-pumped amplifier for further amplification of the amplified seed pulse.   
     
     
         18 . The fiber preamplifier of  claim 17 , further comprising:
 a pumping device configured to provide pulsed pump light; and   a coupler configured to direct the pulsed pump light from the pumping device to a cladding of the coiled, clad-pumped fiber amplifier.   
     
     
         19 . The fiber preamplifier of  claim 18 , further comprising:
 a short wave pass filter coupled between the pumping device and the cladding of the coiled, clad-pumped fiber amplifier,   wherein the short wave pass filter is configured to prevent forward traveling amplified spontaneous emission from damaging the pumping device.   
     
     
         20 . The fiber preamplifier of  claim 10 , further comprising:
 a radio frequency (RF) driver configured to control operation of the AOM.