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  External cavity laserUSPTO Application #: 20070223554Title: External cavity laser Abstract: Embodiments of systems and methods are provided for a tunable laser device. The tunable laser device may include a diffraction grating connected to a pivot arm that pivots the diffraction grating about a pivot point to tune the laser device. In pivoting the diffraction grating about the pivot point, both the wavelength to which the diffraction grating is tuned and the length of the optical cavity may be changed. The length of the pivot arm may be selected to reduce the number of mode hops of the tunable laser device when tuning the laser device over its tuning range. (end of abstract) Agent: Jagtiani + Guttag - Fairfax, VA, US Inventors: Susan Hunter, Vladimir Krneta, Jason Ensher USPTO Applicaton #: 20070223554 - Class: 372102 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070223554. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001]This application makes reference to and claims the priority date of co-pending U.S. Patent Application 60/780,354, entitled "External Cavity Laser", filed Mar. 9, 2006. The entire disclosure and contents of the above application is hereby incorporated by reference. BACKGROUND [0002]1. Field of the Invention [0003]The present invention relates generally lasers, and more particularly, to external cavity lasers. [0004]2. Related Art [0005]The use of an external laser cavity with a spectrally selective element has been used for several decades to create a laser with a narrower spectral linewidth than is available with the non-wavelength selective mirrors in the laser cavity of the typical laser. In addition, the tenability of the spectrally selective element may create a laser with an agile wavelength that may be both narrow in line width and cover a broad tuning range. The spectrally selective element in many non-integrated external cavity lasers may be a diffraction grating. These diffraction gratings may be designed to meet a broad range of laser cavity needs such as size, efficiency, and dispersion. The tuning of the wavelength of the laser may be achieved by adjusting the grating angle of the diffraction grating with respect to the laser beam. [0006]Tuning such a laser by merely adjusting the grating angle may result in the laser occasionally "hopping" from one cavity mode to another cavity mode. A cavity mode (referred to hereafter as a "mode") refers to the integral number of half wavelengths of light at the tuned wavelength that fit within the optical cavity of the laser. Further, these hops from one mode to another are referred to as mode hops. Mode hops may result in the instability of the laser output by the laser system. Thus, it is desirable to reduce the number of mode hops that exist across a tuning range of the laser system. [0007]Accordingly, there is a need for laser systems with improved mode hop performance over the tuning range. SUMMARY [0008]According to a first broad aspect of the present invention, there is provided a laser system comprising: [0009]a light source which provides light; [0010]a lens which collimates the light to provide a collimated coherent light beam; [0011]a diffraction grating which reflects at least a portion of a wavelength of light of the collimated coherent light beam towards the light source; and [0012]a pivot arm connected to the diffraction grating, wherein the pivot arm pivots the diffraction grating to thereby adjust the wavelength of light reflected by the diffraction grating towards the light source as well as adjusting an optical path length. [0013]According to a second broad aspect of the invention, there is provided a method for generating a coherent light beam comprising the following steps: [0014](a) providing a collimated coherent light beam; and [0015](b) pivoting a pivot arm connected to a diffraction grating to adjust a position of the diffraction grating, thereby adjusting a wavelength of light of the collimated coherent light beam reflected by the diffraction grating as well as adjusting an optical path length. [0016]According to a third broad aspect of the invention, there is provided a laser system for generating a coherent light beam comprising: [0017]means for providing a collimated coherent light beam; [0018]means for reflecting at least a portion of a wavelength of light of the collimated coherent light beam; and [0019]means for adjusting a position of the reflecting means to thereby adjust a wavelength of light of the collimated coherent light beam reflected by the reflecting means as well as adjusting an optical path length for the laser system. BRIEF DESCRIPTION OF THE DRAWINGS [0020]The invention will be described in conjunction with the accompanying drawings, in which: [0021]FIG. 1 illustrates an exemplary laser system, in accordance with embodiments of methods and systems of the present invention; [0022]FIGS. 2A and 2B provide a simplified diagram for illustrating a Littrow angle, in accordance with embodiments of methods and systems of the present invention; [0023]FIG. 3 illustrates a simplified exemplary laser system where the pivot point is located directly below the intercept point on the transmission grating, in accordance with embodiments of methods and systems of the present invention; [0024]FIG. 4 provides an exemplary plot illustrating mode number, versus wavelength over the tuning range for an exemplary laser system for various lengths of the pivot arm, in accordance with embodiments of methods and systems of the present invention; [0025]FIG. 5 provides an exemplary plot illustrating mode number, versus wavelength over the tuning range for an exemplary laser system for various lengths of the pivot arm between Pmin and Pmax, in accordance with embodiments of methods and systems of the present invention; [0026]FIG. 6 illustrates a simplified exemplary laser system illustrating various positions for locating the pivot point of a pivot arm, in accordance with embodiments of methods and systems of the present invention; [0027]FIG. 7 illustrates an exemplary laser system in which the alignment of the laser system's components may be adjusted, in accordance with embodiments of methods and systems of the present invention; [0028]FIGS. 8A and 8B illustrate an exemplary pivot arm with an attached transmission grating, in accordance with embodiments of methods and systems of the present invention; [0029]FIGS. 9A and 9B illustrate an exemplary mount, transmission grating and first portion of a pivot arm, in accordance with embodiments of methods and systems of the present invention. 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