An optical apparatus for spectrally shaping a laser beam, comprising: a birefringent optic including a polarization maintaining optical fiber that contributes polarization mode dispersion thereto, the birefringent optic having orthogonal first and second polarization axes, the birefringent optic arranged to receive and transmit the laser beam, the laser beam delivered through a first splice to the birefringent optic, the laser beam received by the birefringent optic being linearly polarized and having an electric-field vector oriented at an oblique angle φ to the first polarization axis, angle φ being a splice angle of the first splice; and a linear polarizer having a polarizing direction, the polarizer arranged to receive the laser beam transmitted through the birefringent optic and to transmit a portion thereof, the polarizing direction oriented at an oblique angle θ to the first polarization axis, the birefringent optic and the polarizer are joined by a second splice, angle θ being a splice angle of the second splice, the portion of the laser beam transmitted through the polarizer having a more-uniform power spectral density than the laser beam received by the birefringent optic; wherein transmission through the birefringent optic induces a wavelength-dependent phase shift between a component of the laser beam parallel to the first polarization axis and a component of the laser beam parallel to the second polarization axis, the wavelength-dependent phase shift producing a wavelength-dependent polarization state of the laser beam transmitted through the birefringent optic, thereby modulating power spectral density in the portion of the laser beam transmitted through the polarizer. a birefringent optic including a polarization maintaining optical fiber that contributes polarization mode dispersion thereto, the birefringent optic having orthogonal first and second polarization axes, the birefringent optic arranged to receive and transmit the laser beam, the laser beam delivered through a first splice to the birefringent optic, the laser beam received by the birefringent optic being linearly polarized and having an electric-field vector oriented at an oblique angle φ to the first polarization axis, angle φ being a splice angle of the first splice; and a linear polarizer having a polarizing direction, the polarizer arranged to receive the laser beam transmitted through the birefringent optic and to transmit a portion thereof, the polarizing direction oriented at an oblique angle θ to the first polarization axis, the birefringent optic and the polarizer are joined by a second splice, angle θ being a splice angle of the second splice, the portion of the laser beam transmitted through the polarizer having a more-uniform power spectral density than the laser beam received by the birefringent optic; wherein transmission through the birefringent optic induces a wavelength-dependent phase shift between a component of the laser beam parallel to the first polarization axis and a component of the laser beam parallel to the second polarization axis, the wavelength-dependent phase shift producing a wavelength-dependent polarization state of the laser beam transmitted through the birefringent optic, thereby modulating power spectral density in the portion of the laser beam transmitted through the polarizer.