Coherent light generators – Particular resonant cavity
Patent
1995-06-01
1997-05-06
Bovernick, Rodney B.
Coherent light generators
Particular resonant cavity
372 96, 372 50, 372 18, 372 33, H01S 305, H01S 318
Patent
active
056278535
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Optically-pumped solid-state lasers have been useful sources of coherent radiation for more than 20 years. In recent years, improvements in laser performance have resulted from the fabrication of semiconductor quantum-well structures. In a quantum-well structure, thin atomic layers of smaller energy bandgap semiconductor material, for example GaAs, are sandwiched between thin layers of wider bandgap material, for example Al.sub.x Ga.sub.(1-x) As, to form potential wells in the conduction and valence bands. Such wells restrict or limit carrier/electron movement to two dimensions. Quantum-well heterostructures generally exhibit more efficient luminescence intensities than bulk crystal heterostructures and therefore, have been incorporated into the active region of semiconductor laser devices.
In current solid-state microchip lasers, the laser cavity geometry determines the volume of a laser mode propagating therein. A typical microchip laser cavity comprises a gain medium disposed between a pair of curved mirrors. Incoherent pump energy, for example laser diode output, is directed into the cavity using various techniques. Certain pumping techniques are more efficient than others.
Laser efficiency is the proportion of pump energy which is converted to coherent output energy. Pump energy directed into the cavity that is not converted to output energy is emitted as wasted incoherent energy or converted into heat. The more pump energy that is wasted, the lower the efficiency of the laser.
In the past, solid-state lasers were side-pumped in a transverse direction with incoherent diodes along the length of the gain medium. Side-pumped lasers are relatively inefficient, because the entire gain medium volume is pumped, with laser gain occurring only in a small central volume of the gain medium. The pump energy is dispersed throughout the gain medium, rather than being concentrated within the volume of the resonant laser mode. This results in inefficient energy conversion.
Recently, end-pumped solid-state lasers have improved conversion efficiency. In end-pumped lasers such as those described in U.S. Pat. No. 4,710,940, incoherent pump energy is longitudinally focused with optics through the entrance and/or exit mirrors into the central portion of the gain medium within the diameter of the resonating laser mode. This technique is thus limited in that the laser mode volume is predetermined by the geometry of the laser cavity, and therefore, the diameter of the pump beam must be matched to the predicted laser mode diameter for efficient operation.
SUMMARY OF THE INVENTION
The present invention is directed to an apparatus and method for stabilizing the transverse mode of laser oscillation in quantum-well semiconductor lasers and solid-state microchip lasers. The apparatus of the invention comprises a substrate preferably of semiconductor material, having first and second opposed faces. A mirror having a predetermined radius of curvature is formed over the first face of the substrate. A quantum-well structure is formed on the second face of the substrate. A second mirror is formed on the quantum-well structure, the first and second mirrors defining a resonant cavity therebetween. A source is provided for electrically or optically pumping the quantum-well layer to produce laser gain. The laser gain causes a laser mode having a particular wavelength and a particular transverse diameter to oscillate. The diameter of oscillating mode is a function of the radius of curvature of the first mirror, the optical length of the resonant cavity, and the wavelength of the oscillating mode.
In another embodiment, the second mirror has a predetermined radius of curvature in addition to the first curved mirror.
In another embodiment, the substrate is formed of semiconductor or other light-transparent material having a positive temperature variant refractive index and the first and second mirror on the substrate are fabricated substantially flat. As the laser is pumped, the absorbed pump light causes heatin
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Kuznetsov Mark E.
Mooradian Aram
Bovernick Rodney B.
Coherent Inc.
Song Yisun
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