An Introduction to Nonlinear Optics and Harmonic generation
- 1. 1 An Introduction to Nonlinear Optics and Harmonic Generation Presented by Shahina Parbin MGCU2023PHY4018 Dept of Physics,MGCUB Semester: 4th Paper code: PHYS4009 Date: 15.04.2025
- 2. 2 Contents Introduction to nonlinear phenomena Linear vs nonlinear optics Harmonic generation Types of Harmonic Generation
- 3. 3 Nonlinear optics: Study of interaction of light in matter. Non-linear optics allows us to show when a very intense light interact with a medium and causes unusual shortest events ever made by humans. Fig shows : Sending infrared light into a crystal yielded this display of green light. Introduction to Nonlinear optics
- 4. 4 When light intensity is high, the electric field becomes strong enough to distort the electron cloud in atoms and molecules beyond the linear limit. This distortion creates nonlinear polarization, which leads to new light frequency and effects. Nonlinear optical process are often referred to as: ‘n-wave mixing process’ where n is the number of photon involved. Fig: shows molecular energy levels in case of nonlinear optics In Non-linear optics
- 5. 5 In linear optical phenomena, the polarization P is directly proportional to the electric field E . But in nonlinear optics, with high-intensity fields, the polarization P(t) can be described by Tayler series expansion in terms of electric field E(t): where χ(1) is linear susceptibility of the medium, and where χ(2) , χ(3) …, are nonlinear susceptibilities. These higher-order terms are responsible for nonlinear optical effects; such as harmonic generation , sum and difference frequency generation , self-focusing etc.
- 6. 6 Application of Nonlinear optics Nonlinear optics has various applications that significantly impact daily life, including: 1. Telecommunications(specially in optical fibers) 2. Commercial lasers 3. sensors 4. Scientific instrumentation 5. and materials processing
- 7. 7 Linear optics- ‘Optics of weak light’ : • Light is deflected or delayed but its frequency is unchanged. • The polarization P of the medium is directly proportional to the electric field E of the light: P=ε 0χ (1) E Non-linear Optics- ‘Optics of intense light’: • In nonlinear optics, polarization includes higher order terms. Linear optics vs Nonlinear optics Linear material response Nonlinear material response
- 8. 8 It is a nonlinear optical process in which n photons with the same frequency interact with the nonlinear material are combined and generate a new photon with n times the energy of initial photons. For example, second harmonic generation (SHG) produces light at twice the frequency of the original light, while third harmonic generation (THG) produces light at three times the frequency. N-th Harmonic generation Harmonic Generation
- 9. 9 Second-Harmonic Generation(SHG) It also known as frequency doubling, is the lowest-order wave- wave nonlinear interaction that occurs in various systems. SHG was first demonstrated by Peter Franken at the University of Michigan in 1961.Initially it was discovered as a nonlinear optical process; in which two photons with the same frequency interact with a nonlinear material, are "combined", and generate a new photon with twice the energy of the initial photons. SHG is widely used, for example, in doubling laser frequencies.
- 10. 10 Third-harmonic Generation (THG) A special case in which the number of photons in the interactions is n=3, if all the photons have same frequency. This process involves the 3rd order nonlinear susceptibility. Another special case in which the number of photons in interaction is n=4.Reported around the year 2000,powerfull laser now enable efficient FHG. This process involves the 4th order nonlinear susceptibility. Fourth-Harmonic Generation(FHG)
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