4𝜋𝜀0𝑎2=5.1×1011𝑉/𝑚 . Second-order nonlinearity estimation 𝜒(2)∝1
𝐸=1.19𝑝𝑚/𝑉 ; And the third -order nonlinearity estimate is 𝜒(3)∝1
𝐸2=3.8 [𝑝𝑚
𝑉]2
. From the Appendix here are two examples : KTP: 𝜒31(2)=2𝑑31=3.9 𝑝𝑚/𝑉; 𝜒32(2)=2𝑑32=7.8 𝑝𝑚/𝑉; 𝜒33(2)=2𝑑32=30.6 𝑝𝑚/𝑉. BBO: 𝜒22(2)=2𝑑22=−4.4 𝑝𝑚/𝑉; 𝜒31(2)=2𝑑31=0.16 𝑝𝑚/𝑉. Most cases in the appendix are within one order of magnitude of the estimate. The magnitude is also affected by atomic and molecular resonances that can further skew the estimate. A couple of values are as follows: fused silica: 𝜒𝑥𝑥𝑥𝑥(3)=258 [𝑝𝑚
𝑉]2
; carbon disulfide (liquid) cw: 𝜒𝑥𝑥𝑥𝑥(3)=
19,200 [𝑝𝑚
𝑉]2
, chalcogenide glass As 2S3: 𝜒𝑥𝑥𝑥𝑥(3)=120 ,000 [𝑝𝑚
𝑉]2
. The values are generally several orders of magnitude larger than predicted by the atomic field estimate alone. Clearly other mechanisms are responsible for third -order nonlinearities. Chapter 2 Problem Solutions 2.1. A plane wave has an electric field given by 0 ˆ E E sin kz t x is incident on a material with a susceptibility given by 01 3i /2 . a) What is the complex amplitude of the electric field? i2
0ˆ A E e x (S2.1) b) What is the phase shift between a polarization induced by the field and the incident field? The relationship between the polarization’s complex amplitude and the field’s complex amplitude is, 0PA (S2.2) Therefore the phase difference is the phase of the complex susceptibility, which is 3 . c) What is the real polarization in this medium induced by the field? 0 0 0 ˆ P E sin kz t x3 (S2.3) or equivalently, 0 0 0 ˆ P E cos kz t x6 (S2.4) 2.2. A plane wave in a vacuum has an electric field given by, 0 ˆ E E cos(kz t )x . a) What i s B
? We use Maxwell’s equation, 2.2, to relate the curl of the electric field to the time derivative of the magnetic field. For a field of the form given here, ˆikz and it . Therefore, 0Eˆ B cos kz t yc
. (S2.5) b) What is the complex amplitude of B ? i0Eˆ B e yc
. (S2.6) c) What are Sand S ? 2
20
00EEBˆ S E H cos kz t zc
. (S2.7) 2
0
0Eˆ Sz2c
. (S2.8)