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![OPTICAL MIXING
The generation of new frequencies with help of nonlinear phenomena is called
optical mixing. Suppose two coherent waves of unequal frequencies, ω1 and ω2
are traversing the material, then
E = E1 cos ω1 t + E2 cos ω2 t
Hence
The second term gives rise to 2ω2. The last term can be expressed as
2ε0 χ2 E1 E2 cos ω1t = ε0 χ2 E1 E2 [cos (ω1 + ω2) t + cos (ω1 – ω2) t]
Thus waves of frequencies ω1, 2ω1, ω2, 2ω2, (ω1+ω2) and (ω1–ω2) are
generated. Using proper optical arrangement it is possible to get sufficiently
intense output at any one of these frequencies.](https://image.slidesharecdn.com/nonlinearopticsedited-170407154552/75/Non-linear-optics-and-SHG-20-2048.jpg)
Uploaded bysahil rajput
Non linear optics and SHG
Nonlinear optics involves intense light interacting with matter to change the light's properties. This allows generating new frequencies of light from the input light. Second harmonic generation produces light with twice the frequency by combining two photons. High harmonic generation using intense lasers can generate coherent x-rays. Phase matching is important for high conversion efficiency in nonlinear optical processes. Applications include optical switching, data storage, and generating coherent x-rays for attosecond science.
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Non linear optics and SHG
- 1.
- 2. Linear Optics vsNon Linear Optics Linear optics- ‘Optics of weak light’: Light is deflected or delayed but its frequency is unchanged. Non-Linear optics-‘Optics of intense light’: We are concerned with the effects that light itself induces as it propagates through the medium.
- 3. Non-Linear optics producesmany exotic events •Nonlinear optics allows us to change the color of a light beam, to change its shape in space and time, to switch telecommunica- tions systems, and to create the shortest events ever made by Man Ex: Sending infrared light into a crystal yielded this display of green light
- 4. In Non-Linear Optics Ifirradiance is high enough vibrations at all frequencies corresponding to all energy differences between populated states are produced.
- 5. Introduction Nonlinear Optics:Study of interaction of light in matter We can control “n” by the light itself or manipulate one beam with the other. Leads to a Great variety of technical innovations.
- 6. Importance of ‘NLO’ Optical wave manipulation is one of the future technologies for optical processing. It has various applications in fiber- optic communications and optoelectronics which makes it an increasingly important topic among electrical engineers.
- 7. Nonlinear polarization Linearmedium: low field intensity Nonlinear medium: high field intensity PED += 0ε EED r 0εεε =⋅= Linear polarization PED += 0ε Nonlinear polarization EP ⋅= χε0 NLL PPEEEP +=+⋅+⋅+⋅= ...3)3(2)2( 0 χχχε NLLlkjijklkjijkjiji PPEEEEEDEP +=++⋅+⋅= ...420 χχε Linear susceptibility tensor 2nd order nonlinear susceptibility tensor 3rd order nonlinear susceptibility tensor Summation over repeated indices χε +=1r i, j, k = x, y, z
- 8. Sum frequency generation(SFG) Difference frequency generation (DFG) 2nd order optical nonlinearity Start with two beams ω = ω1 and ω = ω2 SFG: ω3 = ω1 + ω2 , k3 = k1 + k2 DFG: ω3 = ω1 - ω2 , k3 = k1 - k2 SFG/DFG for photodetection Use a 1060 nm laser to convert 10 μm mid-infrared radiation to 960 nm near-infrared radiation that can be handled by low-cost detectors Sum frequency Pump laser Laser emissionSHG
- 9. Sum frequency generation Exampleof second order nonlinear optical effects 1ω 3ω 2ω = ω1+ω2
- 10. Second harmonic generation (alsocalled frequency doubling or abbreviated SHG) is a nonlinear optical process, in which photons with the same frequency interacting with a nonlinear material are effectively "combined" to generate new photons with twice the energy, and therefore twice the frequency and half the wavelength of the initial photons. Second harmonic generation, as an even-order nonlinear optical effect, is only allowed in media without inversion symmetry. It is a special case of sum frequency generation and is the inverse of half- harmonic generation.
- 11. ∑= γβ γβαβγα ωωωωωχω , )2( 0 )()(),;2(ε)2(EEP ),;2()2( ωωωχαβγ : symmetric under interchange of β and γ. Energy level scheme of SHG process.
- 12. Common SHG materials 800 nm: BBO 806 nm: lithium iodate (LiIO3) 860 nm: potassium niobate (KNbO3) 980 nm: KNbO3 1064 nm: monopotassium phosphate (KH2PO4, KDP), lithium triborate (LBO) and β-barium borate (BBO) 1300 nm: gallium selenide (GaSe) 1319 nm: KNbO3, BBO, KDP, potassium titanyl phosphate (KTP), lithium niobate (LiNbO3), LiIO3, and ammonium dihydrogen phosphate (ADP) 1550 nm: potassium titanyl phosphate (KTP), lithium niobate (LiNbO3)
- 13. SHG Analysis TheSecond harmonic generation efficiency of TMPP was examined by Kurtz and Perry powder technique. A Q- switched mode locked Nd: YAG laser of wavelength 1064 nm with a pulse width of 8 ns and a repetition rate of 10 Hz was allowed to pass through the powdered sample which is kept in a capillary tube. The emission of green light with a wavelength of 532 nm confirms the second harmonic generation efficiency of TMPP. A second harmonic out signal of 64 mV was obtained for an input beam of energy 2.149 mJ /pulse. For the same incident radiation the output signal was observed as 79 mV for KDP. Hence it is found that the SHG efficiency of TMPP crystal is 0.8 times that of standard potassium dihydrogen phosphate (KDP). From this it is evident that the TMPP is a good NLO crystal
- 14. High harmonic generation Spectrumof a Neon HHG source driven by a Ti-sapphire laser. High harmonic generation (HHG) is a non-linear process during which a target (gas, plasma or solid sample) is illuminated by an intense laser pulse. Under such conditions, the sample will emit the high harmonics of the generation beam (above the fifth harmonics). Due to the coherent nature of the process, high harmonics generation is a prerequisite of atto physics.
- 15. Spectrum of aNeon HHG source driven by a Ti-sapphire laser
- 16. Properties High harmonics havea number of interesting properties. They are a tunable table-top source of XUV/Soft X-rays, synchronized with the driving laser and produced with the same repetition rate. The harmonic cut-off varies linearly with increasing laser intensity up until the saturation intensity Isat where harmonic generation stops . The saturation intensity can be increased by changing the atomic species to lighter noble gases but these have a lower conversion efficiency so there is a balance to be found depending on the photon energies required.
- 17. High harmonic generationstrongly depends on the driving laser field and as a result the harmonics have similar temporal and spatial coherence properties . High harmonics are often generated with pulse durations shorter than that of the driving laser. This is due to the nonlinearity of the generation process, phase matching and ionization. Often harmonics are only produced in a very small temporal window when the phase matching condition is met. Depletion of the generating media due to ionization also means that harmonic generation is mainly confined to the leading edge of the driving pulse.
- 18. In a typicalsituation, the electrical fields are traveling waves described by at position X , with the wave vector , where c is the velocity of light in vacuum, and n(Wj) is the index of refraction of the medium at angular frequency Wj . Thus, the second-order polarization at angular frequency At each position X within the nonlinear medium ,the oscillating second order polarization radiates at angular frequency W3 and a corresponding wave vector . Constructive interference ,and therefore a high intensity W3 field will occur if Match making condition Phase matching condition
- 19. efficiency Only when2k1 = k2 will SHG be efficient n(λ1) = n(λ2) General rule for parametric processes SHG, SFG/DFG, THG, FWM momentum conservation 2k1 = k2 2k1 ≠ k2 ~ 100% SHG conversion efficiency is possible by optimizing phase matching!
- 20. OPTICAL MIXING Thegeneration of new frequencies with help of nonlinear phenomena is called optical mixing. Suppose two coherent waves of unequal frequencies, ω1 and ω2 are traversing the material, then E = E1 cos ω1 t + E2 cos ω2 t Hence The second term gives rise to 2ω2. The last term can be expressed as 2ε0 χ2 E1 E2 cos ω1t = ε0 χ2 E1 E2 [cos (ω1 + ω2) t + cos (ω1 – ω2) t] Thus waves of frequencies ω1, 2ω1, ω2, 2ω2, (ω1+ω2) and (ω1–ω2) are generated. Using proper optical arrangement it is possible to get sufficiently intense output at any one of these frequencies.
- 21. The generation of(ω1+ ω2) is called frequency-up conversion and (ω1–ω2) is called frequency-down conversion Crystals like KDP, ADP are used for up conversion while LiNbO3, quartz are used for down conversion. -- Arrangement for generating a new frequency by optical mixing
- 22. Applications: Optical phaseconjugation Optical parametric oscillators Optical computing Optical switching Optical data storage
- 23. Thank You Presented By, SahilRao ASAS