Analyses of the thermal shifts of spectral lines in Nd³⁺-doped LiYF₄ laser crystal

Abstract

The red-shift of spectral line E ₁(R ₁ → Y ₂) and blue-shift of line E ₂(R ₁ → X ₅) with temperature in Nd³⁺-doped LiYF₄ laser crystal are studied by considering both the static contribution due to lattice thermal expansion and vibrational contribution due to electron–phonon interaction. The study is based on the analyses of pressure and temperature dependences of these spectral lines. It is found that for both lines, the static and vibrational contributions result in the blue- and red-shift, respectively. So, the observed red-shift of line E ₁ and blue-shift of line E ₂ are due respectively to the static contribution being smaller and larger than the vibrational one. Also, we infer that the thermal shifts of lines E ₃(R ₁ → Y ₅) and E ₄(R ₂ → Y ₅) are very small because both contributions may be approximately canceled. When both the contributions are contained, whether the red-shift or blue-shift of a spectral line can be fitted with the almost same theoretical expression as that by including only the vibrational contribution used in red-shift in the previous papers if we change the expression concerning electron–phonon interaction coefficient.