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US 5,177,750 AGranted
Misalignment-tolerant, grating-tuned external-cavity laser with enhanced longitudinal mode selectivity
AssigneeHewlett-Packard Company
InventorPaul Zorabedian
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Abstract
A grating tuned external cavity laser having improved mode selectivity and stability. A cylindrical lens is positioned between a laser amplifier and a prism pair beam expander to focus the laser beam to form a linear spot on a grating. The location of the cylindrical lens between the laser amplifier and the prism pair minimizes the optical length of the laser cavity. In this way, the wavelength separation between optical resonance modes is increased, and the mode selectivity and stability of the system is enhanced.
Claims20
A grating tuned external cavity laser system comprising:
- a laser amplifier that emits a laser beam along an optical axis A, said laser beam having a pair of lateral dimensions W.sub.F and W.sub.T where W.sub.P is measured along a direction parallel to an axis P perpendicular to optical axis A and W.sub.T is measured along a direction parallel to an axis T perpendicular to axis A and P, said lateral dimensions W.sub.P and W.sub.T being referred to herein as laser beam height and width, respectively;
- a grating positioned in the path of said laser beam and oriented relative to said laser amplifier to produce a diffraction order that retroflects back to the laser amplifier, thereby forming an external cavity with said laser amplifier where the external cavity feeds back, to the laser amplifier, laser beam energy having an average value;
- wherein said grating is rotatable about axis P to enable tuning of the laser amplifier and the grating contains a set of grating rulings that are substantially parallel to axis P;
- and
- wherein a normal N to a front face of the grating at the intersection of the optical axis with the grating makes an angle .theta. with the optical axis A at the grating;
- a beam expander, positioned in the path of said laser beam between said laser amplifier and said grating, that expands the beam at the grating in a direction substantially perpendicular to the rulings of said grating;
- a cylindrical lens, positioned in the path of said laser beam between said laser amplifier and said beam expander, for reducing the ratio of laser beam height to laser beam width to produce on said grating a laser spot having a ratio height W.sub.P to width W.sub.T much less than 1;
- and
- the cylindrical lens having a focal length falling in part within the beam expander thereby substantially reducing the effective focal length of the laser cavity to produce a shorter optical path length and to improve longitudinal mode selectivity.
6 more elements
A grating tuned, external cavity laser system comprising:
- a laser amplifier with a laser beam output;
- a beam width expander;
- a beam height contractor located between the laser beam output and the beam width expander;
- a grating to reflect the laser beam back through the beam width expander and beam height contractor to the laser amplifier;
- and the beam height contractor having a focal length falling in part within the beam width expander thereby substantially reducing the effective focal length of the laser cavity to produce a shorter optical path length and to improve longitudinal mode selectivity.
2 more elements
An external cavity laser system comprising:
- a laser amplifier with a laser beam output;
- a beam width expander;
- a grating including lines;
- and
- a beam height contractor located between the laser beam output and the grating;
- the beam height contractor being in optical cooperation with the beam width expander such that the beam height contractor has a focal length falling in part within the beam expander thereby reducing the effective focal length of the laser cavity to produce a shorter optical path length and to improve longitudinal mode selectivity;
- and
- the grating being operative to reflect the laser beam back through the beam width expander and beam height contractor to the laser amplifier.
5 more elements
Dependencies are inferred from the claim text.