physics

Parametric process (optics)

Parametric process (optics) is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Parametric process (optics) rather than just read about it. In short: A parametric process is an optical process in which light interacts with matter in such a way as to leave the quantum state of the material unchanged. As a direct consequence of this there can be no net transfer of energy, momentum, or angular momentum between the optical field and the physical system.

Key takeaways

Parametric process (optics) belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Parametric process (optics) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Parametric process (optics) from memory before moving on to harder problems.

Reference excerpt

A parametric process is an optical process in which light interacts with matter in such a way as to leave the quantum state of the material unchanged. As a direct consequence of this there can be no net transfer of energy, momentum, or angular momentum between the optical field and the physical system. In contrast a non-parametric process is a process in which any part of the quantum state of the system changes.

Temporal characteristics Because a parametric process prohibits a net change in the energy state of the system, parametric processes are "instantaneous". For example, if an atom absorbs a photon with energy E, the atom's energy increases by ΔE = E, but as a parametric process, the quantum state cannot change and thus the elevated energy state must be a temporary virtual state. By the Heisenberg Uncertainty Principle we know that ΔEΔt~ħ/2, thus the lifetime of a parametric process is roughly Δt~ħ/2ΔE, which is appreciably small for any non-zero ΔE.

Parametric versus non-parametric processes

Linear optics In a linear optical system the dielectric polarization, P, responds linearly to the presence of an electric field, E, and thus we can write

P = ε 0 χ E = ( n r + i n i ) 2 E , {\displaystyle {\mathbf {P} }=\varepsilon _{0}\chi {\mathbf {E} }=(n_{r}+in_{i})^{2}{\mathbf {E} },}

where ε0 is the electric constant, χ is the (complex) electric susceptibility, and nr(ni) is the real(imaginary) component of the refractive index of the medium. The effects of a parametric process will affect only nr, whereas a nonzero value of ni can only be caused by a non-parametric process. Thus in linear optics a parametric process will act as a lossless dielectric with the following effects:

Refraction Diffraction Elastic scattering Rayleigh scattering Mie scattering Alternatively, non-parametric processes often involve loss (or gain) and give rise to:

Absorption Inelastic scattering Raman scattering Brillouin scattering Various optical emission processes Photoluminescence Fluorescence Luminescence Phosphorescence

Nonlinear optics

In a nonlinear media, the dielectric polarization P responds nonlinearly to the electric field E of the light. As a parametric process is in general coherent, many parametric nonlinear processes will depend on phase matching and will usually be polarization dependent. Sample parametric nonlinear processes:

Second-harmonic generation (SHG), or frequency doubling, generation of light with a doubled frequency (half the wavelength) Third-harmonic generation (THG), generation of light with a tripled frequency (one-third the wavelength) (usually done in two steps: SHG followed by SFG of original and frequency-doubled waves) High harmonic generation (HHG), generation of light with frequencies much greater than the original (typically 100 to 1000 times greater) Sum-frequency generation (SFG), generation of light with a frequency that is the sum of two other frequencies (SHG is a special case of this) Difference frequency generation (DFG), generation of light with a frequency that is the difference between two other frequencies Optical parametric amplification (OPA), amplification of a signal input in the presence of a higher-frequency pump wave, at the same time generating an idler wave (can be considered as DFG) Optical parametric oscillation (OPO), generation of a signal and idler wave using a parametric amplifier in a resonator (with no signal input) Optical parametric generation (OPG), like parametric oscillation but without a resonator, using a very high gain instead Spontaneous parametric down-conversion (SPDC), the amplification of the vacuum fluctuations in the low gain regime Optical Kerr effect, intensity dependent refractive index Self-focusing Kerr-lens modelocking (KLM) Self-phase modulation (SPM), a χ ( 3 ) {\displaystyle \chi ^{(3)}} effect Optical solitons Cross-phase modulation (XPM) Four-wave mixing (FWM), can also arise from other nonlinearities Cross-polarized wave generation (XPW), a χ ( 3 ) {\displaystyle \chi ^{(3)}} effect in which a wave with polarization vector perpendicular to the input is generated Sample non-parametric nonlinear processes:

Stimulated Raman scattering Raman amplification Two-photon absorption, simultaneous absorption of two photons, transferring the energy to a single electron Multiphoton absorption Multiple photoionisation, near-simultaneous removal of many bound electrons by one photon

Worked examples

Example 1 — a first encounter with Parametric process (optics)

Start with the simplest possible case. Write down what Parametric process (optics) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Parametric process (optics) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Parametric process (optics) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Parametric process (optics)

In research: Parametric process (optics) appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Parametric process (optics) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Parametric process (optics) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Nonlinear optics, Quantum optics, so understanding it makes those chapters shorter.
In everyday life: Look for Parametric process (optics) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Parametric process (optics) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Parametric process (optics) means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Parametric process (optics) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Parametric process (optics) in simple terms?

Why does Parametric process (optics) matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Parametric process (optics)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Parametric process (optics).