Optical filter polarizer combination and laser apparatus incorporating this combination
First Claim
1. A laser apparatus comprising:
- first and second reflector means disposed in optical alignment for defining a resonant cavity therebetween;
an active laser medium for producing a beam of coherent electromagnetic radiation disposed between and in optical alignment with said first and second reflector means, andoptical mode control means disposed within said resonant cavity in optical alignment with said laser medium for shaping the optical transmission characteristics of said resonant cavity to maximize transmission of a desired transverse electromagnetic mode of electromagnetic radiation, said control means comprising;
first and second matching phase plates disposed in optical alignment with said laser medium;
said first phase plate comprising a bifringent crystal having a first flat major surface and a second concave major surface with a predetermined radius of curvature and a predetermined center thickness;
said second phase plate comprising a birefringent crystal having a first flat major surface and a second spherically convex major surface with a predetermined radius of curvature equal to the radius of curvature of said concave surface of said first phase plate and a predetermined center thickness equal to the center thickness of said first phase plate; and
a polarizing means disposed in optical alignment with said phase plates for ejecting radiation having a first polarization from said cavity and transmitting radiation having a second polarization orthogonal to said first polarization.
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Accused Products
Abstract
The present invention deals with an optical filter polarizer combination providing a spacial transmission function to polarized incident light. When the light is in the form of a beam the combination may be used to reject extraneous light, or to modify the intensity profile of the beam as a radial or as a linear spacial function (orthogonal to the axis of the beam). The filter employs two lens elements of birefringent materials, with their crystal optical axes mutually orthogonal, and at 45° to the plane of polarization. Spherical lenses are employed for a radial spacial function and cylindrical lenses are employed for a linear spacial function. The combination is useful for mode selection in a stable laser oscillator, for beam quality improvement in a stable/unstable oscillator, and for fill factor enhancement in coupling energy from a laser oscillator to a laser amplifier.
46 Citations
42 Claims
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1. A laser apparatus comprising:
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first and second reflector means disposed in optical alignment for defining a resonant cavity therebetween; an active laser medium for producing a beam of coherent electromagnetic radiation disposed between and in optical alignment with said first and second reflector means, and optical mode control means disposed within said resonant cavity in optical alignment with said laser medium for shaping the optical transmission characteristics of said resonant cavity to maximize transmission of a desired transverse electromagnetic mode of electromagnetic radiation, said control means comprising; first and second matching phase plates disposed in optical alignment with said laser medium;
said first phase plate comprising a bifringent crystal having a first flat major surface and a second concave major surface with a predetermined radius of curvature and a predetermined center thickness;
said second phase plate comprising a birefringent crystal having a first flat major surface and a second spherically convex major surface with a predetermined radius of curvature equal to the radius of curvature of said concave surface of said first phase plate and a predetermined center thickness equal to the center thickness of said first phase plate; anda polarizing means disposed in optical alignment with said phase plates for ejecting radiation having a first polarization from said cavity and transmitting radiation having a second polarization orthogonal to said first polarization. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for controlling the generation of a laser beam in a laser resonant cavity comprising the steps of:
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exciting a laser medium to build up a population inversion in said laser medium; activating a Q-switch disposed in said laser resonant cavity a first time to produce a seed beam of coherent electromagnetic radiation in said cavity; passing said seed beam through a zero order phase retardation unit to produce a beam in which the transverse electromagnetic TEM00 mode has a first polarization and the higher order TEM modes have a second polarization orthogonal to said first polarization; impinging said beam on a polarizing means to transmit said TEM00 mode and to reject said higher order TEM modes from said cavity; activating said Q-switch a second time to cause rapid depletion of population inversion to produce a pulse of coherent electromagnetic radiation within said laser cavity; passing said pulse through said zero order phase retardation unit to produce a polarized pulse; impinging said polarized pulse upon said polarizing means to transmit a single TEM00 mode pulse of oscillating coherent electromagnetic radiation within said cavity; and outputting a portion of said single TEM00 mode pulse from said cavity during each oscillation of said pulse within said cavity. - View Dependent Claims (15)
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16. In a combination exhibiting a spacial transmission function for incident light, including a beam polarized in a P dimension,
A. an optical transmission filter for imposing a differential phase delay upon said light as a continuous function of position, said transmission filter having an optical axis which is concentric with the axis of said beam and comprising: -
1. a first lens of birefringent material of a first center thickness having a first surface which is flat and a second surface which has a predetermined radius of curvature, 2. a second lens of birefringent material of a second cneter thickness having a first surface which is flat and a second surface which has a radius of curvature equal to the radius of curvature of said first lens but of opposite sign, the surfaces of said lenses being oriented orthogonal to and concentric with said optical axis;
the crystal optical axes of said materials being oriented in mutually orthogonal positions along said optical axis and at an angle of 45°
to said P dimension, with said second surfaces adjacent,B. polarizing means aligned with the optical axis of said optical transmission filter for rejecting components of the beam elements having a first polarization, and selecting components of the beam elements having a second polarization, the light derived from said polarizing means exhibiting said modification in intensity. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. Laser apparatus for forming a beam of electromagnetic radiation propagating within said apparatus along the axis thereof, and polarized in a P dimension orthogonal to said axis, comprising:
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A. first and second reflector means concentrically arranged upon said axis and defining a stable optical resonator susceptable of operation in multi modes, B. an active laser medium for producing said beam disposed between said first and second reflector means, concentrically arranged upon said axis, and C. optical mode control means disposed within said resonant cavity, concentrically arranged upon said axis, comprising, 1. an optical transmission filter for imposing a differential phase delay and consequent progressive polarization rotation upon elements of said polarized coherent electromagnetic radiation as a continuous spacial function, and 2. polarizing means to which said filtered radiation is applied, oriented to attenuate spacially filtered components of said radiation associated with a mode sought to be suppressed and to transmit spacially filtered components of said radiation associated with a desired mode. - View Dependent Claims (28, 29, 30, 31)
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32. Laser apparatus for forming a beam of electromagnetic radiation propagating within said apparatus along the axis thereof, and polarized in a P dimension orthogonal to said axis, comprising:
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A. first and second reflector means concentrically arranged upon said axis and defining a stable/unstable optical resonator, stable operation occurring along an S dimension, orthogonal to said axis, to the dimension of stable operation, and to said P dimension, B. an active laser medium for producing said beam disposed between said first and second reflector means, concentrically arranged upon said axis, said laser apparatus having an effective aperture at an S coordinate value referred to said axis, and C. beam enhancement means disposed within said optical resonator concentrically arranged upon said axis comprising; - View Dependent Claims (34)
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- 33. an optical transmission filter for imposing a differential phase delay and consequent progressive polarization rotation of elements of said P polarized coherent electromagnetic radiation as a continuous function of their S coordinate values, andpolarizing means to which said filtered radiation is applied oriented to attenuate spacially filtered elements of said radiation as a continuous function of said S coordinate value, said function producing a zero attenuation on-axis, which increases to a miximum attenuation at the maximum S coordinate value of said aperture to enchance said beam.
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36. In combination:
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A. means for supplying a beam of light propagating along a prescribed axis and polarized in a P dimension orthogonal to said axis, said beam exhibiting symmetrical intensity profile peaking on said beam axis and diminishing gradually toward the beam perimeter; B. optical intensity profile control means having an optical axis coincident with said beam axis for imposing greater rectangularity upon said profile, comprising; 1. an optical transmission filter for imposing a differential phase delay and consequent polarization rotation upon elements of said polarized beam as a continuous spacial function, in which a substantial differential phase delay occurs on said beam axis, a zero differential phase delay occurs at an intermediate distance, changing in sense at this distance, and a substantial delay again occurs at the perimeter of the beam, and 2. polarizing means to which said filtered beam is applied, oriented to provide substantial attenuation on-axis, zero attenuation at said intermediate distance and a substantial attenuation at the beam perimeter, and C. beam amplification means having an active medium dimensioned to accept said modified intensity profile for enhancing the filling of said medium.
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40. In combination:
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A. means for supplying a beam of light propagating along a prescribed axis and polarized in a P dimension orthogonal to said axis, said beam exhibiting a symmetrical intensity profile peaking on said beam axis and diminishing gradually toward the beam perimeter along an S dimension orthogonal to said axis and to said P dimension, B. optical intensity profile control means having an optical axis coincident with said beam axis for imposing greater rectangularity to said S dimension profile, comprising; 1. an optical transmission filter for imposing a differential phase delay and consequent polarization rotation upon elements of said polarized beam as a continuous spacial function in whcih a substantial differential phase delay occurs on said beam axis, a zero differential phase delay occurs at an intermediate S dimension, changing in sense at this intermediate S dimension, and a substantial delay again occurs at a maximum S dimension at the perimeter of the beam, and 2. polarizing means to which said filtered beam is applied, oriented to provide substantial attenuation on-axis, zero attenuation at said intermediate S dimension and a substantial attenuation at said maximum S dimension at the beam perimeter, and C. a beam amplification means having an aperature dimensioned to accept said modified intensity profile. - View Dependent Claims (42)
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Specification