non linear optics
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This document compares and contrasts linear and nonlinear optics. In linear optics, light propagates through a medium without changing frequency, while in nonlinear optics the medium's response depends on light intensity. Nonlinear optics involves effects where the induced polarization in a medium does not linearly depend on the electric field of the light. This allows frequency conversion via processes like second harmonic generation and sum frequency generation. Materials can exhibit a nonlinear refractive index, leading to self-focusing or defocusing of high intensity light beams. Nonlinear optical effects enable applications like frequency conversion, optical limiting, and all-optical signal processing.
non linear optics
- 1. Linear Optics vs Non Linear Optics Linear optics- ‘Optics of weak light’: Light is deflected or delayed but its frequency is unchanged. Superposition principle holds Non-Linear optics-‘Optics of intense light’: We are concerned with the effects that light itself induces as it propagates through the medium. Superposition principle not valid
- 2. In Linear optics A light wave acts on a molecule, which vibrates and then emits its own light wave that interferes with the original light wave.
- 3. In Non-Linear Optics If irradiance is high enough vibrations at all frequencies corresponding to all energy differences between populated states are produced.
- 4. OPTICS – A LIGHT MATTER INTERACTION Nonlinear optics (NLO) is the study of interaction of intense laser light with matter. NLO sample input output
- 5. Light Matter interaction E2 E2 hν hν E1 E1 Spontaneous Absorption Emission
- 6. Stimulated Emission E2 hν hν hν E1 Stimulated Emission
- 7. m
- 8. Properties of Laser Beam A laser beam •Is intense •Is Coherent Optical power density •Has a very low divergence Focused laser beam E ~ 1010 V/m
- 9. How does optical nonlinearity arise The strength of the electric e field of the light wave should hν a0 be in the range of atomic fields N Eat = e / a 2 0 a0 = / me 2 2 Eat ≈ 2 ×10 V/m10
- 10. Optical Nonlinearity Applied Electric field distorts the cloud and displace the electron Compare this with mass on a spring Separation of charges gives rise to a dipole moment Dipole moment per unit volume is called the polarisation + ++= -- F= - kx E
- 12. When electromagnetic waves propagate in a material, the atoms and molecules oscillate at the frequencies of the electric field associated with waves. The field associated with these EM waves polarizes the molecules in the medium, displacing them from their equilibrium positions and induces a dipole moment, p, given by p=qd q is the electric charge and d is the field induced displacement. The polarization P, i.e. the dipole moment per unit volume, resulting from this induced dipole is given by P= ϵ χ E 0 P=Nqd N is the electron density in the medium. The polarizing effect of the field on the molecular dipoles depends both on the properties of the medium and on the field strength E.
- 13. When the intensity of Output the incident light to a material system increases the response of medium is no longer ? linear P=Nqd Input intensity
- 14. Like loaded spring F= -kx m P= ϵ0 χ E P = ε 0 χ (1) E + χ (2) E 2 + χ (3) E 3 + ... E = Eo cosωt
- 15. 1.Permanent Polarization 2.First order Polarization 3.Second order Polarization 4.Third Order Polarization
- 16. Second Harmonic Generation 2ω ω χ ( 2) ω
- 17. Third Harmonic generation ω ω χ ( 3) 3ω
- 18. OPTICAL MIXING E = E1 cosω1t +E2 cosω2t P ( 2 ) = χ ( 2) ( E1 cos ω1t + E 2 cos ω 2 t ) 2 cos(ω1 +ω2 ) & cos(ω −ω2 ) 1
- 19. Sum Frequency Generation ω2 ω2 χ ( 2) ω 3 = ω1 + ω 2 ω1 ω1 ω ω 2 3 ω1
- 20. Difference Frequency Generation ω2 ω2 χ ( 2) ω 3 = ω1 − ω 2 ω1 ω1 ω2 ω1 ω3
- 21. FOCUSING OF LIGHT BY LENS focus
- 22. Refractive Index with Intensity P = 0 εχE + 0 εχ E L 3 3 ε n= ε0 D = εE = ε0 E + P =( ε0 (1 +χ ) +ε0 χ E )E L ( 3) 2
- 23. ε = ε 0 (1 + χ ) + ε 0χ E L 3 2 χ3 n = (1 +χL )1/ 2 (1 + E 2 )1/ 2 1 +χL ≈n 0 +n 2 E 2 0
- 24. Nonlinear Refractive Index n = n0 + n2 I n0 c 12π 2 (3) where I= | E (ω ) |2 n2 = 2 χ 2π n0 c
- 25. Self focusing and self defocusing χ ( 3) The laser beam has Gaussian intensity profile. It can induce a Gaussian refractive index profile inside the NLO sample.
- 26. Z-scan Set-up Lens Sample Aperture Cell Nd:YAG Detector Laser D2 +Z -Z Detector D1 Power Meter Computer z.swf
- 27. Z- Scan Signature 1.2 Normalised Transmittance 1 0.8 0.6 0.4 0.2 -20 -10 0 10 20 Z (mm) Normalised Transmittance 1.2 1 0.8 0.6 0.4 -20 -10 0 10 20 Z mm
- 28. Different Class of NLO Materials Inorganic Lithium niobium oxide, Potassium titanile Phosphate Ammonium dihydrogen phosphate, Potassium dihydrogen phosphate, Barium Metaborate
- 29. Organics Materials Low cost Ease of fabrication Integrating in to a single devices Easy to do fine tuning of its NLO properties by turning its Chemical structure Low dielectric constant Inherent synthetic flexibility High optical damage threshold
- 30. Structural requirement - ++= + D A D A
- 31. Enhancement of NLO response Science 281 (1998) 1653 TNLO enhancement by Increase conjugation length Create D-π-A- π -D structure A- π -D- π –A structure
- 32. •New Frequency Generations •Different Wavelength lasers from the same Laser Source •Optical limiting
- 33. Applications: Output fluence Input fluence
- 34. Waveguide Inscriptions Lab on a Chip
- 35. Optical Signal Processing 1. Switching and routing are carried out electronically and processing in the electronic domain 2. Optical transmission in optical domain 3. Detection and processing in the electronic domain again 1 2 3 to a single Unit