Cryogenically cooled 946nm Nd:YAG laser

Yoon, Soojin; Mackenzie, Jacob I.

doi:10.1364/oe.22.008069

Cited by 26 publications

(28 citation statements)

References 16 publications

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“…We believe this is the first time that absorption bands associated with RE doping have been observed in Al 2 O 3 transmission spectra and strongly evidence that the Nd 3+ dopant is optically active within the ceramic matrix 53 . The center of the Nd 3+ absorption bands in Al 2 O 3 are slightly blue shifted (~2.5 nm) in comparison with that for Nd:YAG single crystals 51, 52 . The absorption bands are broadened in Nd:Al 2 O 3 to Δ λ ~23 nm (FWHM) from ~Δ λ ~2 nm compared to Nd:YAG 53 , which is consistent with our observations that the Nd 3+ is found on multiple doping sites within the alumina matrix.…”

Section: Discussionmentioning

confidence: 76%

“…One remarkable difference in the Nd:Al 2 O 3 transmission spectra is the presence of the absorption bands centered at λ = 583 nm (2.12 eV), 745 nm (1.85 eV), and 806 nm (1.54 eV), which correspond to the 4 G 5/2 , 4 F 7/2 , and 4 F 5/2 Stark transitions from the 4 I 9/2 manifold 51, 52 . We believe this is the first time that absorption bands associated with RE doping have been observed in Al 2 O 3 transmission spectra and strongly evidence that the Nd 3+ dopant is optically active within the ceramic matrix 53 .…”

Section: Discussionmentioning

confidence: 99%

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Gain in polycrystalline Nd-doped alumina: leveraging length scales to create a new class of high-energy, short pulse, tunable laser materials

et al. 2018

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Traditionally accepted design paradigms dictate that only optically isotropic (cubic) crystal structures with high equilibrium solubilities of optically active ions are suitable for polycrystalline laser gain media. The restriction of symmetry is due to light scattering caused by randomly oriented anisotropic crystals, whereas the solubility problem arises from the need for sufficient active dopants in the media. These criteria limit material choices and exclude materials that have superior thermo-mechanical properties than state-of-the-art laser materials. Alumina (Al2O3) is an ideal example; it has a higher fracture strength and thermal conductivity than today’s gain materials, which could lead to revolutionary laser performance. However, alumina has uniaxial optical proprieties, and the solubility of rare earths (REs) is two-to-three orders of magnitude lower than the dopant concentrations in typical RE-based gain media. We present new strategies to overcome these obstacles and demonstrate gain in a RE-doped alumina (Nd:Al2O3) for the first time. The key insight relies on tailoring the crystallite size to other important length scales—the wavelength of light and interatomic dopant distances, which minimize optical losses and allow successful Nd doping. The result is a laser gain medium with a thermo-mechanical figure of merit of Rs~19,500 Wm−1 a 24-fold and 19,500-fold improvements over the high-energy-laser leaders Nd:YAG (Rs~800 Wm−1) and Nd:Glass (Rs~1 Wm−1), respectively. Moreover, the emission bandwidth of Nd:Al2O3 is broad: ~13 THz. The successful demonstration of gain and high bandwidth in a medium with superior Rs can lead to the development of lasers with previously unobtainable high-peak powers, short pulses, tunability, and high-duty cycles.

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Section: Discussionmentioning

confidence: 76%

Section: Discussionmentioning

confidence: 99%

Gain in polycrystalline Nd-doped alumina: leveraging length scales to create a new class of high-energy, short pulse, tunable laser materials

et al. 2018

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“…To be able to calculate the ETU coefficient with any degree of confidence the other parameters within equations 1-4 need to be known to a high degree of accuracy. We conducted a detailed spectroscopic characterization of the different crystals studied, using a setup similar to that described in [3], in addition to including a polarizer, placed after the crystal, to allow for the absorption cross sections for the different optical axes of the anisotropic crystals to be measured. The ETU coefficients are measured using an adaptation of the open aperture Z-scan technique [4].…”

Section: Methodsmentioning

confidence: 99%

“…Calculated pump radii were 510 µm, 360 µm, 280 µm and 265 µm for 0.3, 0.6, 1.0 and 1.1 at.% doped crystal with lengths of 42.4 mm, 21.2 mm, 12.7 mm, and 11.6 mm, respectively. Pump absorption coefficients were calculated using the room temperature case of the equation given by Yoon et al [3]. For the 946 nm quasi-four-level transition the ~7x smaller emission cross section, which also suffers a weak reabsorption loss, has a significantly higher laser threshold, exacerbated by the effect of ETU that becomes quite significant at modest output coupling values.…”

Section: Nd:yagmentioning

confidence: 99%

Energy transfer upconversion measurements for popular neodymium-doped crystals

et al. 2015

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We report our investigations on measuring the energy transfer upconversion (ETU) parameter in various neodymiumdoped laser crystals (YAG, YVO 4 , GdVO 4 , KGW, and YLF) via the z-scan technique. Starting with a simple two-level macro-parameter spatially dependent rate equation model we obtain a good correlation for Nd:YAG at different concentrations and crystal temperatures, however the other crystals illustrate significant deviation between simulation and measurement. Currently we attribute this difference to additional ion-ion interactions in the respective samples, for which a more detailed model is currently being considered. Of the tested materials Nd:YAG appears to have the lowest ETU macro parameter, at around 0.35 x10 -16 cm 3 /s for a 0.6 at.% doping concentration, compared with nominally thrice this for 0.5 at% Nd:YLF and almost an order of magnitude higher for the 0.5 at.% vanadates (YVO 4 and GdVO 4 ). These values are significant for determining additional heat load in the respective gain media, especially when trying to increase the output power/energy from lasers employing these crystals, typically achieved by increasing the pump and cavity mode size.

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“…Maintaining the same thermal load conditions, whilst lowering the temperature of the heat sink surrounding the Nd:YAG crystal, which is an artificial example as the spectroscopic proprieties of the gain medium also change [13], a decrease in the maximum temperature rise at the center of the crystal is obtained. This is due to the corresponding increase in the thermal conductivity as shown in Fig.…”

Section: Temperature Profile For Different Coolant Temperaturesmentioning

confidence: 99%

Analytical thermal model for end-pumped solid-state lasers

Cini

Mackenzie

2017

Appl. Phys. B

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their performance has capitalized on improving diode-laser brightness and power. Further power-scaling, however, is fundamentally limited by the thermo-optical properties of the gain medium and the induced optical distortions, primarily driven by the quantum defect between pump and the emission wavelengths. Alternatively, the geometry of the gain medium can be optimized to enhance thermal management and minimize the thermal-lensing effects, such as the thin-disk [1], fibre [2], or slab architectures [3], which have demonstrated multi-kW average powers. Nonetheless, for many applications, the end-pumped bulk architecture still holds an important position for its simplicity and robust performance.The basic design strategy for these lasers has been to try to mitigate the effects of the induced thermal-lensing and aberrations [4]. As such, it is important to understand the induced temperature distribution over the active volume of interest, that is, where the cavity mode passes through the excited region of the gain medium. Typically, this involves numerical simulations solving the heat equation with finiteelement algorithms, having almost completely replaced analytical solutions due to the complexity of the necessary assumptions made to obtain exact expressions. Analytical solutions, though, are unquestionably important: they highlight qualitative and quantitative features of underlying physical phenomena and provide more accurate solutions in far less time than numerical calculations, particularly if trying to perform parameter-dependence studies. One strict assumption generally made in determining the exact solution for the temperature profile along an end-pumped solid-state laser is that the thermal conductivity of the crystal is not significantly dependent on temperature [5]. While a reasonable assumption for many active media, operating at and above room temperature (RT), it is generally not valid when cooled to a cryogenic temperature (CT) [6]. Here, the gradient for Abstract Fundamentally power-limited by thermal effects, the design challenge for end-pumped "bulk" solid-state lasers depends upon knowledge of the temperature gradients within the gain medium. We have developed analytical expressions that can be used to model the temperature distribution and thermal-lens power in end-pumped solid-state lasers. Enabled by the inclusion of a temperature-dependent thermal conductivity, applicable from cryogenic to elevated temperatures, typical pumping distributions are explored and the results compared with accepted models. Key insights are gained through these analytical expressions, such as the dependence of the peak temperature rise in function of the boundary thermal conductance to the heat sink. Our generalized expressions provide simple and time-efficient tools for parametric optimization of the heat distribution in the gain medium based upon the material and pumping constraints.

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Cryogenically cooled 946nm Nd:YAG laser

Cited by 26 publications

References 16 publications

Gain in polycrystalline Nd-doped alumina: leveraging length scales to create a new class of high-energy, short pulse, tunable laser materials

Gain in polycrystalline Nd-doped alumina: leveraging length scales to create a new class of high-energy, short pulse, tunable laser materials

Energy transfer upconversion measurements for popular neodymium-doped crystals

Analytical thermal model for end-pumped solid-state lasers

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