Questions tagged [non-linear-optics]

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How can I rotate the piezoelectric tensor?

For a 3m crystal, the piezoelectric tensor or equivalently the nonlinear optical susceptibility is the following; $$\begin{bmatrix}0&0&0&0&d_{15}&-d_{22}\\\ -d_{22}&d_{22}&...
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15 views

Maximum delay between n photons for multi-photon ionization

Given an IR laser with intensities that allow for a Keldysh parameter smaller than 1 in a given sample. I was wondering, what is the allowed timely separation distance between two IR photons such that ...
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Refractive index values of the solution less than that of the solvent. Why does that happen?

I have been doing an experiment for finding the third-order nonlinear susceptibilties of organic molecules using Degenerate Four-Wave Mixing (DFWM) at femtosecond regime. For the calculation of the ...
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56 views

Is it possible to solve those differential equations (with complex numbers)?

I'm trying to solve this equation, I don't know where to begin with. Is it feasible ? If so how should I solve it ? https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-20-7-7454&id=230426 https:/...
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35 views

What causes this high frequency “noise” in HHG spectra?

Looking at high harmonic spectra, one can often see that peaks corresponding to higher harmonics look more and more noisy and seem to be drowned out by the noise. For example, one such spectrum is ...
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50 views

Numerical simulation for spontaneous parametric down conversion

I want to numerically simulate the SPDC (spontaneous parametric down conversion) process. I have a basic background on nonlinear and quantum optics — I am a graduate student and just took a few ...
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20 views

Calculating the absorption cross-section for Helium in a strong oscillating external IR field -> AC Stark Shift (Autler-Townes Splitting)

I try to obtain the absorption cross-section for atomic helium, in a strong and oscillating IR field, for when a second - XUV - pulse is probing the system. I think the only way of doing this is to ...
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2answers
135 views

Why are there only odd harmonics at High Harmonic Generation?

I'm trying to understand why in High Harmonic Generation (HHG) the spectrum only consist out of odd multiples of the driving frequency. Many sources state "because of symmetry" but they do not clearly ...
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20 views

What is the difference between classical nonlinear optics and multiphoton physics?

Nonlinear optics is usually looked at through a classical lens for most purposes. I do a Taylor expansion of the material polarization in terms of light-field strengths and we can derive all the ...
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15 views

What is the physical significance of the elements of the nonlinear susceptibility?

I'm trying to understand the physical significance of the various elements of the nonlinear susceptibility tensors. My best attempt at understanding this is to say that the first index corresponds to ...
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74 views

Electromagnetic energy density in a nonlinear medium

The energy density associated with the electric field in a linear medium of permitivity $ \epsilon $ is given as $$ U = \frac{1}{2}\epsilon\left | E \right |^{2} $$ As Robert Boyd mentions in the ...
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8 views

Why chi 2 process does initiate self focussing effects?

Why we cant see intensity dependent refractive index effects in chi 2 process? Non linear optics#Boyd
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80 views

Derivation of Hamiltonian in non-linear optics

Update 2: one half of the answer to this question can be found here and the other half in the second half of this post. I asked this question a few hours ago, but decided to re-post it because I ...
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1answer
82 views

Focusing a Gaussian beam into a nonlinear crystal

Boyd analyzes in his book (Boyd's book), section 2.10.3, the case of harmonic generation using a focused Gaussian beam and he mentions that an analytic solution can be evaluated for certain special ...
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1answer
146 views

How does optical “self-torque” make sense in terms of Maxwell's equations?

I saw an article in Science (arXiv:1901.10942) that describes "self-torque" of light. My understanding is that a series of ultrafast optical pulses with different angular momenta combine in some ...
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1answer
51 views

Why we use $i\hbar(\hat A -\hat A^\dagger)$ in Parametric Down-Conversion?

When we descirbe the degenerate parametric oscillator or the Parametric Down-Conversion, we can use the hamitonian: $$\hat{H}=\hat H_0+\hat H_{int}+\hat H_{irr}$$ \begin{array}{l} \hat H_0=\hbar\omega ...
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24 views

What is the Holo-Exchange symmetry of the tensor $\chi^{(2)}$?

In a paper by Lu-Ming Duan and Guang-Can Guo, they develop an alternative approach to quantising the EM field in a nonlinear and inhomogeneous media. In this derivation, they use the holo-exchange ...
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45 views

Do the results of this laser experiment demonstrate nonlinear optical phenomenon?

In my photonics class, we conducted an experiment to observe the Beer-Lambert law and the effects of filters(absorption, transmittance, and reflection). We shined a red(632nm) 5mW Helium-Neon laser ...
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42 views

Derivation of Yurke-Stoler state

The evolution of a coherent state $\vert\alpha\rangle$ in a Kerr-nonlinear medium $H=\Omega (a^\dagger a)^2$ is given by $$ \vert \psi(t) \rangle = e^{-\vert\alpha\vert^2/2}\sum_{n=0}^{\infty} \dfrac{\...
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64 views

Phase Matching in a Non linear crystal

I am working with Second Harmonic Generation using a LBO crystal. My pump beam is 795nm and I want to generate blue light using Collinear SHG in LBO. I have perused a lot of resources on the internet ...
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40 views

Pump Probe Spectroscopy Zero Delay

I am setting up a Non Degenerate Pump Probe Experimental Setup, in my lab, as part of my Master's Project. Due to the constraints of the way the lasers have been set up in the lab, I am unable to ...
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1answer
98 views

Coherent state under Kerr evolution

I have a bosonic mode associated to the usual operators $a$, $a^\dagger$. I'm interested in knowing the evolution of a coherent state $\vert \alpha \rangle = e^{\alpha a^\dagger - \alpha^\ast a}\vert ...
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255 views

Maxwell's equations, nonlinear media, and dynamic response

Maxwell's equations in the vacuum with electric permittivity $\epsilon_0$ and magnetic permeability $\mu_0$ are given as: $$\nabla \cdot \vec E = \frac{\rho}{ \epsilon_0}$$ $$\nabla \cdot \vec B = 0$...
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76 views

Optimal pump wavelength for frequency doubling in periodically poled media

Background I am currently working on achieving second harmonic generation (SHG) in periodically poled lithium niobate (PPLN) using a 1560 nm pump laser. PPLN makes use of quasi-phase-matching of the ...
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37 views

What is the relationship between the nonlinear susceptibility and the effective nonlinear coefficient?

Oftentimes, I see equations for non-linear optics expressed in terms of the non-linear susceptibility tensor. Other times, however, I see these same equations expressed in terms of an effective non-...
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1answer
39 views

What are the material restrictions for a $\chi^{3}$ non-linear optical material?

For instance, I know that $\chi^{2}$ materials need to lack inversion symmetry, but what about $\chi^{3}$ materials?
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113 views

Furry's theorem and spontaneous parametric down-conversion

In spontaneous parametric down-conversion, a single photon interacts with a nonlinear medium to produce a pair of lower energy photons. It is observed that energy, momentum, and orbital-angular-...
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46 views

Non-linear optics - solve differential equations coupled with the finite difference method [closed]

I have these three differential equations in which I need to solve numerically: $$ \frac{dn_0}{dt}= -n_0(t)W_{01}(t) + n_1(t)K_{10} $$ $$ \frac{dn_1}{dt}= -n_1(t)W_{12}(t) - n_1(t)K_{10} + n_2(t)K_{...
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1answer
85 views

Spin conservation in spontaneous parametric down-conversion (SPDC)

If one pump photon "decays" through the process of spontaneous parametric down-conversion into two photons how can the spin be conserved?
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1answer
163 views

How to calculate the dispersion parameter of a Fiber?

I am writing a presentation about DCF Fibers. From many articles i am reading, the dispersion parameter of Fibers are given. But it is not shown how it has been calculated. For example ,in this ...
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95 views

When is the permittivity tensor not Hermitian?

I understand that a permittivity tensor is symmetric if there is no absorption. On the other hand is it always Hermitian? Under what cases would that not be the case?
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36 views

What is the gain control technique used in optics?

In optics, it is said that The gain bandwidth and gain flatness of Amplifiers are enhanced utilizing gain control techniques.What techniques are they referring to ? I know the automatic volume ...
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122 views

Difference-frequency generation: physical interpretation

Sum-frequency generation is easy for my to understand. Two photons combine their energies in a nonlinear medium and out comes one photon with the sum of both energies. But Difference-frequency ...
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101 views

Do radio beams self-focus in the interstellar medium?

Summary: In a plasma, electromagnetic waves create a ponderomotive force that pushes electrons and ions out of the way. Thus, in an intense laser beam, electrons tends to move away from the areas ...
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121 views

Higher-order dispersion in non-linear optics

In many cases, dispersion of an optical medium is presented by saying that the dependence of the wavenumber $k$ on the (angular) frequency $\omega$ can be expanded in Taylor series as: $$ k(\omega) = ...
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1answer
86 views

Paraxial approximation in nonlinear optics [closed]

I have a question about the paraxial approximation in nonlinear optics, it is different from the one in linear optics. and i'm confused about the difference between them, can anyone clarify this ...
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3answers
179 views

Frequency Chirp, Instantaneous Frequency and Photons

I understand ideas coming from Optics, such as the concept of frequency chirp and instantaneous frequency, and their use in nonlinear optics. However, I am struggling in giving them an intuitive ...
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89 views

Is second harmonic generation a special case of high harmonic generation?

That might be a strange question, but while I was researching for these topics, I never found an explicit statement that would answer that question. (That might be because of the different ...
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45 views

Observation of Strange Pattern with He-Ne Laser passing through a sample of Chlorophyll

We Designed in our lab an experiment with 5mW He-Ne laser, passing through Chlorophyll, which was extracted from Hibiscus rosa-sinensis leaves dipped in Ethanol. The resultant pattern we observed on ...
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1answer
188 views

Refractive index of Noble Gases at high pressure

How/where can I find(estimate) the refractive index of noble gases like argon and krypton? How does the refractive index of argon and krypton depend on the pressure, specifically high pressures of up ...
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1answer
100 views

Problem in derivation of nonlinear optics wave equation

Consider Maxwell's equations in a general medium without free charges or currents: $$\nabla\cdot\vec{D} = 0 \tag{1}$$ $$\nabla\cdot\vec{B} = 0 \tag{2}$$ $$\nabla\times\vec{E} = -\frac{\partial \vec{B}...
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47 views

Can light of different frequencies interfere with each other?

In principle I'm aware of superposition and how it works. Nevertheless I'm not really able to answer the following: Will two light beams of different frequencies interfere with each other? More ...
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143 views

Why non-linear fiber capacity limit decrease for higher signal-noise ratios?

In fiber optics communication, there is the concept of nonlinear Shannon limit (see e.g. this article), implying that the communication capacity of an optical fiber decreases for high SNR. I don’t ...
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1answer
160 views

What is difference between transmission and transparency?

I learned about the spectral hole burning. On Wikipedia, it said Spectral hole burning is the frequency-selective bleaching of the absorption spectrum of a material, which leads to an increased ...
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1answer
67 views

How does “coherence” contribute to inverting a two-level system?

In laser physics I am told that inverting a two-level system is not possible, since it will become transparent once the inversion reaches 50% and no longer be able to absorb more photons. This makes ...
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1answer
81 views

Plasma in solids

One way to create plasma is to focus a very powerful laser pulse to a small beam waist. In gaseous atoms, ionization will occur, yielding a soup of ions and electrons, which we call a plasma. But ...
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120 views

Pockels Cell reverse propagation

Pockels Cells are called "voltage controlled waveplates", since the voltage changes the birefringence of the material, leading to the same birefringence induced change of total polarisation plane than ...
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1answer
129 views

Purity of a quantum state in the Heisenberg picture

The purity of a quantum state is defined as $$ \gamma = \mathrm{Tr}(\rho^2) $$ In the Schrödinger picture, it's easy to use this formula to see how the purity of the system changes as the system ...
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43 views

Footage of SHG in smoke/fog

I am looking for a footage of second harmonic generation performed with laser and a non-linear crystal in which infrared light is converted to visible light. But I also want that to be performed in ...
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88 views

How is 'nonlinear optics' related to 'nonequilibrium'?

According to what I found, nonlinear optical process is related to nonequilibrium physics - nonequilibrium green's function (Keldysh green's function/formalism) appears in nonlinear optics. However, ...