Laser source comprising amplifier and adaptive wavefront/polarization driver

• US 20050201429A1
• Filed: 03/15/2004
• Published: 09/15/2005
• Est. Priority Date: 03/15/2004
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Rice, Robert R., Wickham, Michael G., Komine, Hiroshi
• Granted Patent: US 7,088,743 B2
• Time in Patent Office: Days
• US Class Current: 372/27
• CPC Class Codes: B23K 26/0604 by a combination of beams
• CPC Class Codes: B23K 26/0608 in the same heat affected zone [HAZ] B23K26/0613, B23K26/0619 take precedence
• CPC Class Codes: B23K 26/705 Beam measuring device
• CPC Class Codes: G01J 9/02 by interferometric methods using interferometers for measuring optically the linear dimensions of objects G01B9/02
• CPC Class Codes: H01S 3/0014 Monitoring arrangements not otherwise provided for photometry G01J1/00, e.g. G01J1/4257; radiation pyrometry G01J5/00; measuring coherence of light G01J9/00; measuring wavelength of light G01J9/00, e.g. G01J9/0246; measuring optical pulses G01J11/00; calorimetrically measuring power of laser beams G01K17/003
• CPC Class Codes: H01S 3/005 Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B
• CPC Class Codes: H01S 3/0064 Anti-reflection devices, e.g. optical isolaters absorbing layers for marking or protecting purposes in laser working B23K26/50; magneto-optical non-reciprocal devices G02F1/093, G02F1/0955
• CPC Class Codes: H01S 3/0604 in the form of a plate or disc
• CPC Class Codes: H01S 3/06758 Tandem amplifiers
• CPC Class Codes: H01S 3/094003 the pumped medium being a fibre
• CPC Class Codes: H01S 3/094038 End pumping
• CPC Class Codes: H01S 3/0941 of a laser diode
• CPC Class Codes: H01S 3/1304 by using an active reference, e.g. second laser, klystron or other standard frequency source H01S3/139 takes precedence; automatic control of electronic generators H03L7/00
• CPC Class Codes: H01S 3/1305 Feedback control systems
• CPC Class Codes: H01S 3/1307 Stabilisation of the phase
• CPC Class Codes: H01S 3/2375 Hybrid lasers H01S3/07 takes precedence
• CPC Class Codes: H01S 3/2383 Parallel arrangements

Abstract

A hybrid laser source including a solid state laser driven by an array of fiber laser amplifiers, the inputs of which are controllable in phase and polarization, to compensate for distortions that arise in the solid state laser, or to achieve desired output beam properties relating to direction or focus. The output beam is sampled and compared with a reference beam to obtain phase and polarization difference signals across the output beam cross section, at spatial positions corresponding with the positions of the fiber laser amplifiers providing input to the solid state laser. Therefore, phase and polarization properties of the output beam may be independently controlled by predistortion of these properties in the fiber laser amplifier inputs.

Claims

1. A laser source scalable to provide a high power output beam of good beam quality, the laser source comprising:

a solid state laser amplifier providing a high power output beam;

an array of laser fiber amplifiers providing an input beam to the solid state laser;

a phase and polarization sensor, for sensing phase and polarization variations in a cross section of the output beam from the solid state laser; and

means for controlling phase and polarization of elements of the array of laser fiber amplifiers, to achieve phase and polarization control through the cross section of the output beam;

whereby precise phase and polarization control is effected even the output beam is of high power.

2. A laser source as defined in claim 1, wherein the phase and polarization sensor comprises:

means for sampling the output beam throughout its cross section; and

means for comparing the phase and polarization of output beam samples with a reference beam;

and wherein the means for controlling phase and polarization comprises separate phase and polarization control elements for each element of the array of laser fiber amplifiers, and wherein the output beam phase and polarization is conformed to qualities of the reference beam.

3. A laser source as defined in claim 2, wherein the reference beam and multiple inputs to the array of laser fiber amplifiers are all derived from a common master oscillator.

4. A laser source as defined in claim 1, wherein the array of laser fiber amplifiers comprises:

multiple inputs derived from a common master oscillator;

a diode pump source coupled to the laser fiber amplifiers to provide pump power; and

an array of collimating lenses coupled to corresponding fiber outputs and arranged in a closely packed configuration to launch the multiple fiber outputs as an input to the solid state laser.

5. A laser source as defined in claim 4, wherein:

the solid state laser is diode pumped.

6. A laser source as defined in claim 4, wherein:

the solid state laser is selected from the group consisting of a rod laser, a slab laser, a disk laser and a heat capacity laser.

7. A laser source as defined in claim 4, wherein the phase and polarization sensor comprises:

a beam sampler for obtaining a sample of the output beam;

a reference beam source derived from the common master oscillator;

optical means for comparing the sample of the output beam with the reference beam; and

a sensor lens array for spatially sampling the sensed phase and polarization differences across the output beam cross section.

8. A hybrid laser source scalable to high powers, the laser source comprising:

a master oscillator and related amplifier producing a laser seed beam of desired quality and spectral content;

a plurality of fiber laser amplifiers coupled to receive the laser seed beam derived from the master oscillator;

a plurality of diode pump sources coupled to the fiber laser amplifiers to provide amplification;

a collimator lens array coupled to receive output beams from the fiber laser amplifiers and configured in a compact configuration to provide a composite output beam from the fiber laser amplifiers;

a solid state laser positioned to receive the composite output beam from the fiber laser amplifiers, and pumped by diodes to generate an amplified output beam;

a phase and polarization sensor positioned in the solid state laser output beam and configured to produce a plurality of phase and polarization difference signals corresponding spatially to the positions of lenses in the collimator lens array;

a phase and polarization controller, for generating electrical control signals to achieve a desired predistortion of phase and polarization of the optical beams input to the fiber laser amplifiers; and

a plurality of phase and polarization control elements coupled to the fiber laser amplifier inputs to achieve the desired predistortion of phase and polarization.

9. A hybrid laser source as defined in claim 8, wherein the phase and polarization distortion signals applied to the fiber laser amplifier inputs are selected to conform the solid state laser output beam to the phase and polarization qualities of a reference beam derived from the master oscillator.

10. A hybrid laser source as defined in claim 8, wherein the phase and polarization distortion signals applied to the fiber laser amplifier inputs are selected to effect a desired wavefront tilt or other distortion in the solid state laser output beam.

11. A method for generating a laser beam of high power and good beam quality, comprising the steps of:

generating a seed beam of desired beam quality and spectral content;

applying the seed beam to multiple fiber laser amplifiers;

pumping the fiber laser amplifiers to produce an array of amplified output beams from the fiber laser amplifiers;

focusing the output beams from the fiber laser amplifiers into a solid state laser;

pumping the solid state laser to produce a composite output beam;

sampling the composite output beam and sensing phase and polarization differences at a plurality of spatial positions in a cross section of the composite output beam, the spatial positions corresponding to the positions of the fiber laser amplifiers providing input to the solid state laser;

generating phase and polarization control signals corresponding to the sensed polarization differences; and

predistorting the phase and polarization of the seed beam applied to the inputs of the fiber laser amplifiers, to achieve desired phase and polarization properties in the output beam from the solid state amplifier.

12. A method as defined in claim 11, wherein:

the sensed phase and polarization differences result from a comparison between the phase and polarization of a reference signal and the phase and polarization properties sampled in the cross section of the solid state laser output signal; and

the step of predistorting the phase and polarization has the effect of compensating of phase and polarization distortions arising in the solid state laser.

13. A method as defined in claim 11, wherein:

the step of predistorting the phase and polarization has the effect of achieving a desired change in wavefront tilt or focus of the solid state laser output beam.