DIFFRACTIVE OPTICAL ELEMENTS FOR TRANSFORMATION OF MODES IN LASERS

• US 20150340835A1
• Filed: 07/10/2015
• Published: 11/26/2015
• Est. Priority Date: 05/02/2012
• Status: Active Grant

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Inventors: Sridharan, Arun K., Pax, Paul H., Heebner, John E., Drachenberg, Derrek R., Armstrong, James P., Dawson, Jay W.
• Granted Patent: US 9,373,928 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G02B 5/1814 structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings G02B5/189 takes precedence
• 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 3/0085 Modulating the output, i.e. the laser beam is modulated outside the laser cavity
• CPC Class Codes: H01S 3/06729 Peculiar transverse fibre profile
• CPC Class Codes: H01S 3/10015 by monitoring or controlling, e.g. attenuating, the input signal
• CPC Class Codes: H01S 3/10023 by functional association of additional optical elements, e.g. filters, gratings, reflectors
• CPC Class Codes: H01S 3/10053 Phase control
• CPC Class Codes: H01S 3/1307 Stabilisation of the phase
• CPC Class Codes: H01S 3/2333 Double-pass amplifiers
• CPC Class Codes: H01S 3/2383 Parallel arrangements

Abstract

Spatial mode conversion modules are described, with the capability of efficiently transforming a given optical beam profile, at one plane in space into another well-defined optical beam profile at a different plane in space, whose detailed spatial features and symmetry properties can, in general, differ significantly. The modules are comprised of passive, high-efficiency, low-loss diffractive optical elements, combined with Fourier transform optics. Design rules are described that employ phase retrieval techniques and associated algorithms to determine the necessary profiles of the diffractive optical components. System augmentations are described that utilize real-time adaptive optical techniques for enhanced performance as well as power scaling.

Claims

1. An apparatus, comprising:

a HOM ribbon fiber amplifier configured to receive and amplify a higher order mode (HOM) input beam to produce an amplified HOM beam;

a first diffractive optical element (DOE) configured to impart a predetermined phase onto said amplified HOM beam to produce an amplified fundamental mode beam; and

a second DOE configured to transform the phase of said amplified fundamental mode beam into a single fundamental mode beam.

2. The apparatus of claim 1, wherein said first DOE comprises a first phase plate and wherein said second DOE comprises a second phase plate.

3. The apparatus of claim 1, wherein said first phase plate is configured to impart the requisite amount of phase shift across said amplified HOM beam to produce said amplified fundamental mode beam that is spread into multiple lobes matching the spatial pattern of said amplified HOM beam and wherein said second phase plate is configured to produce a single Gaussian beam from said amplified fundamental mode beam.

4. The apparatus of claim 1, wherein said HOM ribbon fiber amplifier comprises a core having a first width configured to propagate a single mode and a second width orthogonal to said first width, wherein said second width is configured to propagate multiple modes or beams.

5. A method, comprising:

providing an apparatus comprising;

a HOM ribbon fiber amplifier configured to receive and amplify a higher order mode (HOM) input beam to produce an amplified HOM beam;

a first diffractive optical element (DOE) configured to impart a predetermined phase onto said amplified HOM beam to produce an amplified fundamental mode (TEM₀₀) amplitude profile; and

a second DOE configured to transform the phase of said amplified amplitude profile into a single fundamental mode (TEM₀₀) beam;

directing said higher order mode (HOM) input beam into said HOM ribbon fiber amplifier to produce said amplified HOM beam;

directing said amplified HOM beam onto said first DOE to produce said amplified fundamental mode (TEM₀₀) amplitude profile; and

directing said amplified fundamental mode beam onto said second DOE to produce said single fundamental mode (TEM₀₀) beam.

6. The method of claim 5, wherein said first DOE comprises a first phase plate and wherein said second DOE comprises a second phase plate.

7. The method of claim 5, wherein said first phase plate is configured to impart the requisite amount of phase shift across said amplified HOM beam to produce said TEM₀₀ amplitude profile at the input plane of said second DOE, wherein said second DOE is configured to produce a TEM₀₀ mode beam from said amplified TEM₀₀ amplitude profile.

8. The method of claim 5, wherein said HOM ribbon fiber amplifier comprises a core having a first width configured to propagate a single mode and a second width orthogonal to said first width, wherein said second width is configured to propagate multiple modes or beams.