Apparatus and Method for Controlling Laser Processing of a Remote Material

Abstract

Apparatus for controlling laser piercing of a remote material (10), which apparatus comprises: at least one piercing laser (1) for emitting laser radiation (2) for piercing the remote material (10), which laser radiation (2) is characterized by a first wavelength (16); a probe laser (3) for emitting a probe signal (4) for monitoring the piercing of the remote material (10); beam delivery optics (5) configured to direct the laser radiation (2) and the probe signal (4) onto the material (10); at least one detector (6) for detecting optical radiation (7) that is emitted or reflected by the material (10) in response to the probe signal (4); and an electronic filter (8) for filtering an electronic signal (9) emitted by the detector (6) in response to the detector (6) detecting the optical radiation (7); and the apparatus being characterized in that the probe laser (3) is configured such that the probe signal (4) is able to be modulated by a modulation signal (13); and the electronic filter (8) comprises a phase sensitive detector (14) which is configured to receive the electronic signal (9) and the modulation signal (13) and to provide phase sensitive detection of the electronic signal (9), which phase sensitive detection is used to improve a signal to noise ratio of an amplitude of the electronic signal (9), thereby enabling detection of a reduction in the amplitude of the electronic signal (9), which reduction is indicative of the laser radiation (2) piercing the remote material (10).

1 . Apparatus for controlling laser piercing of a remote material, which apparatus comprises:
 at least one piercing laser for emitting laser radiation for piercing the remote material, which laser radiation is characterized by a first wavelength;   a probe laser for emitting a probe signal for monitoring the piercing of the remote material;   beam delivery optics configured to direct the laser radiation and the probe signal onto the material;   at least one detector for detecting optical radiation that is emitted or reflected by the material in response to the probe signal; and   an electronic filter for filtering an electronic signal emitted by the detector in response to the detector detecting the optical radiation;   
       and the apparatus being characterized in that
 the probe laser is configured such that the probe signal is able to be modulated by a modulation signal; and 
 the electronic filter comprises a phase sensitive detector which is configured to receive the electronic signal and the modulation signal, and to provide phase sensitive detection of the electronic signal, which phase sensitive detection is used to improve a signal to noise ratio of an amplitude of the electronic signal, thereby enabling detection of a reduction in the amplitude of the electronic signal, which reduction is indicative of the laser radiation piercing the remote material. 
 
     
     
         2 . Apparatus according to  claim 1  wherein the electronic filter comprises a sampler for sampling the electronic signal in synchronism with the modulation signal. 
     
     
         3 . Apparatus according to  claim 1  wherein the probe signal has a second wavelength, and wherein the first wavelength is different from the second wavelength. 
     
     
         4 . Apparatus according to  claim 3  and including an optical filter configured to filter the optical radiation emitted or reflected by the material in response to the probe signal. 
     
     
         5 . Apparatus according to  claim 1  wherein the probe laser is a pulsed laser. 
     
     
         6 . Apparatus according to  claim 5  wherein the modulation signal is synchronized with a pulse repetition frequency of the pulsed laser. 
     
     
         7 . Apparatus according to  claim 5  wherein the pulsed laser is a nanosecond pulsed fibre laser. 
     
     
         8 . Apparatus according to  claim 5  wherein the piercing laser is characterized by a maximum power and the probe laser is characterized by a peak power, and the probe laser is selected such that the peak power is greater than the maximum power. 
     
     
         9 . Apparatus according to  claim 1  wherein the piercing laser is a continuous wave laser. 
     
     
         10 . Apparatus according to  claim 9  and comprising a plurality of the piercing lasers. 
     
     
         11 . Apparatus according to  claim 10  wherein the piercing lasers have the same first wavelength. 
     
     
         12 . Apparatus according to  claim 11  wherein the beam delivery optics is configured to coherently combine the laser radiation emitted from the piercing lasers. 
     
     
         13 . Apparatus according to  claim 10  wherein the piercing lasers have different first wavelengths, and the beam delivery optics comprises a diffraction grating configured to combine the laser radiation emitted from the piercing lasers. 
     
     
         14 . Apparatus according to  claim 1  wherein the detector is configured to be adjacent to the probe laser. 
     
     
         15 . A method for controlling laser piercing of a remote material, which method comprises:
 providing at least one piercing laser for emitting laser radiation for piercing the remote material, which laser radiation is characterized by a first wavelength;   providing a probe laser for emitting a probe signal;   directing the laser radiation and the probe signal onto the material;   detecting optical radiation that is emitted or reflected by the material in response to the probe signal with at least one detector; and   filtering an electronic signal emitted by the detector in response to the optical radiation with an electronic filter;   
       and the method being characterized in that it includes the following steps:
 modulating the probe signal with a modulation signal; 
 inputting both the electronic signal and the modulation signal to the electronic filter; 
 performing phase sensitive detection in the electronic filter in order to improve a signal to noise ratio of an amplitude of the electronic signal; and 
 using the amplitude of the electronic signal to control the piercing of the remote material with the laser radiation. 
 
     
     
         16 . A method according to  claim 15  wherein the laser radiation is directed over a free-space distance of at least ten metres. 
     
     
         17 . A method according to  claim 15  wherein the free-space distance is at least one hundred metres. 
     
     
         18 . A method according to  claim 17  wherein the free-space distance is at least one thousand metres. 
     
     
         19 . A method according to  claim 15  wherein the method includes the steps of providing a plurality of the piercing lasers and coherently combining the laser radiation emitted by the piercing lasers. 
     
     
         20 . A method according to  claim 15  wherein the method includes the steps of providing a plurality of the piercing lasers and spectrally combining the laser radiation emitted by the piercing lasers.