Thermal properties of borate crystals for high power optical parametric chirped-pulse amplification

Abstract

The potential of borate crystals, BBO, LBO and BiBO, for high average power scaling of optical parametric chirped-pulse amplifiers is investigated. Up-to-date measurements of the absorption coefficients at 515 nm and the thermal conductivities are presented. The measured absorption coefficients are a factor of 10-100 lower than reported by the literature for BBO and LBO. For BBO, a large variation of the absorption coefficients was found between crystals from different manufacturers. The linear and nonlinear absorption coefficients at 515 nm as well as thermal conductivities were determined for the first time for BiBO. Further, different crystal cooling methods are presented. In addition, the limits to power scaling of OPCPAs are discussed.

First experimental results towards a 100 W wavelength tunable femtosecond OPCPA

“…1 in Ref. 18 ), and furthermore, typical protective coatings can cause a large absorption. In addition, in Table 1.…”

“…Amongst the wide variety of nonlinear crystals, borate crystals -beta-barium borate (BBO), lithium triborate (LBO) and bismuth triborate (BiBO) -are well-established materials, 18 and are used in the near-infrared (∼ 800 nm) OPCPA of ultrabroadband, high repetition lasers. A summary of some important parameters is given in Table 1.…”

“…However, because of its relatively low bandgap (E g ), nonlinear absorption at the OPCPA-pump wavelength of 515 nm leads to significant heating at high energy and power levels. 18 In addition, the broadest gain bandwidth is offered by BBO and LBO. 19 Therefore, we can restrict our attention to LBO and BBO.…”

“…20,21 The thermal conductivities at room temperature (κ ∥ to the phase matching (PM) direction) and the average linear absorption coefficient at 515 nm in bulk (α515) and taken from Ref. 18 d eff Furthermore, a new technique was developed based on thermal imaging of the nonlinear crystals under high power, high intensity laser radiation. This method was more sensitive to local nonlinear absorption maxima within the volume as well as on the surfaces.…”

BBO sapphire compound for high-power frequency conversion

“…This is induced by different lenses employed for collimation, changing the beam diameter via a telescope and focusing of the high power laser beam coming from the fiber amplifiers. The beam diameter and divergence of the radiation emitted from the amplifier fibers in the employed laser system are only slightly changing with average power 22 . All these changes are the same for the BBO single crystal and the stack, since they originate from other optical components located in the high power beam path before the SHG stage.…”