Efficient high-power frequency doubling of distributed Bragg reflector tapered laser radiation in a periodically poled MgO-doped lithium niobate planar waveguide
Spotlight summary: Since the first laser was built in 1960, scientists working in the field of physics of light-matter interaction have aspired to a laser with the highest possible monochromaticity, stability, and intensity of emission, which would be ideal for further theoretical modeling and numerous applications. However, the development of a laser system with close-to-perfect beam parameters faces certain difficulties. For the visible range of wavelengths, for example, solid-state lasers are generally based on the principle of upconversion (i.e., conversion of photons with lower energy to photons with higher energy). The practical design of such solid-state lasers is based mostly on the application of either special upconversion media doped by rare-earth elements or nonlinear optical crystals. In both cases the efficiency of light conversion from infrared (IR) to visible is low, and sophisticated design arrangements are necessary even to slightly increase it. Two methods among those commonly considered to increase an efficiency of the frequency conversion are a high power of pump laser source or a multipassing IR light through the crystal. However, the intracavity nonlinear conversion (multipass arrangement) requires additional efforts to stabilize the output intensity because of uncontrollable coexistence of several longitudinal modes in the resonator, which causes the so-called mode beating and, therefore, a noticeable instability of the laser output. As a result, the natural desire of scientists of having a nearly perfect laser source is often realized in a bulky, complicated, and nontransportable system that requires periodical tuning of optical elements. Until now, the development of efficient, compact, robust, powerful lasers with stable output and narrow linewidth remains to be a vital goal of contemporary laser design.
In a contrast to other numerous scientific publications on lasers design, this Optics Letters paper reports a remarkably elegant solution based on hybrid microtechnology. The key points of this solution are (1) the development of special semiconductor structures for a high-power, tapered laser diode (LD) with extremely low divergence and Bragg reflectors for wavelength stabilization, optimized for chip technology; (2) precisely calculated and optimized parameters of all-optical components; and (3) high-precision mounting of the LD along with the minioptics and nonlinear crystal on micro-optical bench.
As a result of the application of this elegant hybrid technology, the authors achieved more than 1 W of 532 nm green laser emission with single-pass optical IR to visible conversion of 26%. A special semiconductor structure developed for high-power, narrow line LD emission allowed the generation of second harmonic directly, without an additional stage of solid-state laser pumping by the LD. Because of the high power, narrow line, and perfectly designed waist of the input LD emission in a nonlinear crystal, high frequency conversion efficiency in a single pass was achieved. This design allowed the authors to reject the traditional intracavity second-harmonic generation scheme and make the laser portable, robust, and reliable.
The modern semiconductor technology provides inexpensive LDs emitting at a fixed wavelength in a broad IR range. Because of this possibility, the technology described in this article has an excellent prospective for the production of reliable, robust, cost-effective, efficient, and stable single-frequency lasers in the visible wavelength range for commercial and scientific applications, particularly in Raman microspectrometry and portable flow cytometers.
-- Andrey N. Kuzmin
Technical Division: Optoelectronics
ToC Category: Optical Devices
|OCIS Codes:||(140.2020) Lasers and laser optics : Diode lasers|
|(190.2620) Nonlinear optics : Harmonic generation and mixing|
|(230.4320) Optical devices : Nonlinear optical devices|
|(230.7390) Optical devices : Waveguides, planar|
|(140.3515) Lasers and laser optics : Lasers, frequency doubled|
|(250.5960) Optoelectronics : Semiconductor lasers|
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