Scaling CW diode-end-pumped Nd:YAG lasers to high average powers

Tidwell, S. C.; Seamans, J. F.; Bowers, Mark S.; Cousins, A. K.

doi:10.1109/3.135219

Cited by 243 publications

(74 citation statements)

References 23 publications

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“…However, progress in power scaling of TEM operation has been limited by thermal fracture of the laser crystal [2]. Nowadays, the avoidance of thermally induced fracture plays a key role in laser design.…”

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confidence: 99%

Efficient high-power diode-end-pumped TEM_00 Nd:YVO_4 laser with a planar cavity

2000

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Abstract-We demonstrate a compact and efficient diode-endpumped TEM 00 laser with output power of 25.2 W for 52 W of incident pump power by use of a single YVO 4 crystal with a Nd concentration of 0.3 at.%. In Q-switched operation 21-W of average power at a pulse repetition rate of 100 kHz and 1.1-mJ pulse energy at a pulse repetition rate of 10 kHz were produced. At 10 kHz, the pulse width is around 10 ns and the peak power is higher than 100 kW.Index Terms-Diode-pumped, Nd-doped laser, Q-switched. DIODE-PUMPED solid-state lasers with high beam quality and output power in the range of several tens of watts are rapidly becoming the preferred laser sources in micromachining applications [1]. However, progress in power scaling of TEM operation has been limited by thermal fracture of the laser crystal [2]. Nowadays, the avoidance of thermally induced fracture plays a key role in laser design. The Nd:YVO crystal has been often used in diode-end-pumped lasers owing to its high absorption over a wide pumping wavelength bandwidth and large stimulated emission cross section at the lasing wavelength. Unfortunately, the thermal shock parameter of Nd:YVO is 3 times lower than that of Nd:YAG. Therefore, the maximum output power of Nd:YVO is usually several times lower than that of Nd:YAG. For a conventional 1.0 at% Nd:YVO crystal, the maximum output power limited by thermal fracture is approximately 6 W for one-end pumping [3].In our recent study [4], we found that the fracture-limited pump power, , for an end-pumped laser is inversely proportional to the absorption coefficient, i.e., (1) where is the fractional thermal loading, is the absorption coefficient at the pump wavelength and is the thermal shock parameter which depends on the mechanical and thermal properties of the host material. The absorption coefficient of the laser crystal linearly increases with increasing the dopant concentration. In other words, lower Nd concentrations can be beneficial in extending the fracture-limited pump power. Even though lowering dopant concentrations can extend the fracture-limited pump power, the efficiency in the TEM mode may be reduced because of a poorer overlapping efficiency. Therefore, a good laser design must integrate these factors to obtain the optimum concentration for scaling the output power at high beam quality. Our theoretical analysis [4] shows that the dopant concentration in Nd:YVO crystal must be larger than 0.25 at.% to obtain a slope efficiency in TEM mode higher than 45%. In this letter, we demonstrate an efficient diode-pumped Nd:YVO laser with a continuouswave (CW) TEM output of 25 W by use of a Nd concentration of 0.3 at.%. The performance in -switched operation of this laser is also reported. Fig. 1 is a schematic of the three-mirror laser cavity utilized in the experiment. The pump power consists of two 30-W fiber-coupled diode-laser arrays (FAP-81-30C-800-B) with the output wavelength of the lasers at 25 C ranging from 807 to 810 nm. The fibers were drawn into round bundles of 0.8-mm diameter and a numer...

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confidence: 99%

Efficient high-power diode-end-pumped TEM_00 Nd:YVO_4 laser with a planar cavity

2000

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“…The phase profile induced by the pumping beam creates a lensing effect inside the cavity and in this way the plane-plane cavity of a monolithic microchip laser reduces to an equivalent planoconcave resonator configuration. Thermal lensing and thermal beam distortions in end pumped solid state laser systems have been studied extensively for a long time both in edgeand face-cooled configurations [7][8][9][10]. Frauchiger et al gave the pump power induced temperature distribution as a power series expansion in the case of edge-cooled rod [9] whereas Cousins gave the temperature distributions as a Fourier-Bessel expansion for facecooled systems under thin disk approximation [10].…”

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confidence: 99%

Effect of absorbed pump power on the quality of output beam from monolithic microchip lasers

et al. 2002

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The dependence of the beam propagation factor (M 2 parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively studied. Our investigations show that the M 2 parameter is related to the absorbed pump power through two parameters (α and β ) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration associated with the thermal lens induced by the pump beam. Such dependency of M 2 parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd 3· -doped GdVO 4 crystal and the values of α and β parameters were estimated from the experimentally measured data points.

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“…There are several approaches used to estimate the thermal lens in end-pumped lasers, such as pump power or cavity stability test [9 -11], interferometric methods [12,13], and probe-beam techniques [14,15]. For a laser resonator with a plane end-mirror there must be a beam waist positioned at its surface.…”

Section: Laser Characterization Techniquementioning

confidence: 99%

Thermal lensing characterization of a high-radiance 946nm planar waveguide laser

Mackenzie

2012

SPIE Proceedings

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Abstract:We present the characterization of the in-plane thermal lens in a quasi-four-level Nd:YAG planar waveguide (PW) laser configured for high-radiance operation with an external stable-cavity. Our approach utilises the measurement of the laser's output irradiance distribution at the near-and far-field positions concurrently in order to obtain the "real time" beam propagation parameter and thus beam quality factor, M 2 . Coupled with the knowledge of the intra-cavity-thermallens-dependent beam sizes at an intra-cavity beam waist, the power dependent effective thermal lens focal length was characterized. A thermal lens focal length of >450 mm was obtained at all incident pump powers up to the maximum level of 87 W. This characterization enabled the build of a 29 W 946 nm PW laser with a record output radiance of 4.3 TWm -2 sr -1 .

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Scaling CW diode-end-pumped Nd:YAG lasers to high average powers

Cited by 243 publications

References 23 publications

Efficient high-power diode-end-pumped TEM_00 Nd:YVO_4 laser with a planar cavity

Efficient high-power diode-end-pumped TEM_00 Nd:YVO_4 laser with a planar cavity

Effect of absorbed pump power on the quality of output beam from monolithic microchip lasers

Thermal lensing characterization of a high-radiance 946nm planar waveguide laser

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