Numerical treatment of the temperature distribution in end-pumped composite laser rods

Dement'ev, A. S.

doi:10.3952/lithjphys.47316

Cited by 8 publications

(13 citation statements)

References 24 publications

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“…In conclusion, we find that heat effects play a major role in diode pumped solid-state lasers and should be taken into account in laser design. To overcome the undesired thermal effects in laser crystals, we need to develop accurate methods to measure thermal lensing, mathematical models to predict thermal effects accurately [11,12], and various compensation techniques to reduce the effects of thermal lensing [13][14][15][16].…”

Section: Discussionmentioning

confidence: 99%

Finite Element Analysis of Thermal Effects in Diode End-Pumped Solid-State Lasers

El-Daher

2017

Advances in Optical Technologies

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Thermal effects are the main obstacle to getting high power and good beam quality in diode end-pumped solid-state lasers. In this work, a theoretical investigation of thermal effects in single and dual end-pumped solid-state lasers is carried out using finite element analysis (FEA) for a selected number of widely used laser producing materials, namely, Nd:YAG, Yb:YAG, and Nd:KGW. Crystals with different dimensions are also investigated both in single and in dual end-pumped configuration. Finally, the effect of using composite crystals on thermal lensing is investigated. An experiment to measure the thermal focal length for two different crystals was carried out and a comparison with FEA computed focal length of the thermal lens is made. In all cases studied in this work, results show clear effects of thermal lensing with some differences depending on crystal type, pump power, and size.

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Section: Discussionmentioning

confidence: 99%

Finite Element Analysis of Thermal Effects in Diode End-Pumped Solid-State Lasers

El-Daher

2017

Advances in Optical Technologies

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“…Sometimes, the coefficient ξ = 0.7 is used in calculations [10,17]. The experimental data analysed recently in [14] is well fitted by ξ = 1.0 in the temperature range between 160 and 500 K. This dependence was used in [2,6,7,9,10,[12][13][14][15][16] with different values of the coefficient of thermal conductivity k 0 at the reference temperature T r . Now we think that the most validated value of k 0 is 0.105 W/(cm K) at T r = 300 K.…”

Section: General Solution Of Heat Transfer Equationmentioning

confidence: 99%

“…The numerical treatment of the temperature distribution in end pumped laser rods showed [13,22] that neglecting longitudinal z-derivatives in the steadystate heat transfer equation with radially symmetric heating distribution does not strongly change temperature distribution for conventional (noncomposite) rods with the length L significantly longer than the rod radius R when rod end faces are only cooled by ambient air. Thus, neglecting the longitudinal heat flow through the end faces of AE, the heat transfer equation becomes rather simple: .…”

Section: General Solution Of Heat Transfer Equationmentioning

confidence: 99%

“…A simplified model for the dependence of thermal lensing on the transverse intensity profile of the pump beam was first developed for the temperature independent parameters of the active element (AE) [1,8]. However, another reason for the occurrence of spherical aberrations in the AE is the temperature dependence of its thermal conductivity [2,3,7,9,10,[12][13][14][15][16][17]. It follows from this dependence that the radial temperature distribution has higher nonparabolic terms even for homogeneous heat loading in the AE [6,7].…”

Section: Introductionmentioning

confidence: 99%

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Conditions for reducing spherical thermal aberrations in transversally pumped YAG rods

Brickus¹,

Dement'ev²

2016

Lith. J. Phys.

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Temperature dependences of the thermal conductivity and thermo-optic coefficient are often neglected when thermal lensing in laser crystals is investigated, though their influence is very significant. In this paper, the general solution of heat transfer equation with temperature dependent thermal conductivity is found in an integral form, which is very convenient for analytical and numerical analysis. Using this solution, the possibility to eliminate spherical aberration by a proper choice of the pump parabolicity parameter is investigated in detail. The inaccuracies in the definition of optical path differences used in a few previous works for the case of temperature dependent thermo-optic coefficient are explained. It is shown that the use of a correct definition increases the value of the parabolic coefficient at which the elimination of spherical aberrations may be realized as compared with the original work of Hodgson and Weber. It is also found that nearly the same shapes of pumping are required for elimination of spherical aberrations for both radial and tangential polarization.

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“…A particularly simple solution of the heat transfer equation can be found [28] for the polynomial radial heating distribution where the normalized thermal loading on the rod axis is expressed through the full loading power P h of a cylindrical AE with radius R and length L. The known results for uniform and parabolic pump beam distributions follow from this solution. The solutions for top-hat and Gaussian pump beam distributions can also be found [52].…”

Section: Refractive Index Change For Special Pump Beam Distributionsmentioning

confidence: 99%

On the use of photoelastic effect and plane strain or plane stress approximations for the description of thermal lensing

Brickus¹,

Dement'ev²

2016

Lith. J. Phys.

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Correct use of the photoelastic effect for the description of thermally induced refractive index change is discussed and the analytical relations between thermo-optic coefficients at zero stresses and zero strains are found for all classes of cubic crystals. These relations may be useful for the investigation of thermal effects in very promising sesquioxide class m3 laser crystals. An accepted set of elasto-optical coefficients of the YAG crystal and an alternative one found in the literature were used in numerical simulations. Significant differences in the calculated thermo-optic coefficients and induced birefringence are found using different sets of these coefficients. Misunderstandings related with the so-called photoelastic coefficients are resolved and new expressions for these coefficients are found. It is shown that the incorrect use of these coefficients for different pump beam distributions can lead to significant discrepancies for thermally induced birefringence. It is also shown that common use of the generalized thermo-optic coefficients significantly overestimates the values of optical power of thermal lenses when they are applied to the laser rods with lengths several times longer than their diameter.

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Numerical treatment of the temperature distribution in end-pumped composite laser rods

Cited by 8 publications

References 24 publications

Finite Element Analysis of Thermal Effects in Diode End-Pumped Solid-State Lasers

Finite Element Analysis of Thermal Effects in Diode End-Pumped Solid-State Lasers

Conditions for reducing spherical thermal aberrations in transversally pumped YAG rods

On the use of photoelastic effect and plane strain or plane stress approximations for the description of thermal lensing

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