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  2. Michelson–Morley experiment - Wikipedia

    en.wikipedia.org/wiki/Michelson–Morley_experiment

    (b) The fringes have been shifted to the left by 1/100 of the fringe spacing. It is extremely difficult to see any difference between this figure and the one above. (c) A small step in one mirror causes two views of the same fringes to be spaced 1/20 of the fringe spacing to the left and to the right of the step.

  3. Two-photon absorption - Wikipedia

    en.wikipedia.org/wiki/Two-photon_absorption

    Schematic of energy levels involved in two photons absorption. In atomic physics, two-photon absorption (TPA or 2PA), also called two-photon excitation or non-linear absorption, is the simultaneous absorption of two photons of identical or different frequencies in order to excite an atom or a molecule from one state (usually the ground state), via a virtual energy level, to a higher energy ...

  4. Isosbestic point - Wikipedia

    en.wikipedia.org/wiki/Isosbestic_point

    Isosbestic points are also used in clinical chemistry, as a quality assurance method, to verify the accuracy in the wavelength of a spectrophotometer. This is done by measuring the spectra of a standard solution at two different pH conditions (above and below the pK a of the substance).

  5. Interferometry - Wikipedia

    en.wikipedia.org/wiki/Interferometry

    The nonlinear combination of the input signals creates two new signals, one at the sum f 1 + f 2 of the two frequencies, and the other at the difference f 1 − f 2. These new frequencies are called heterodynes. Typically only one of the new frequencies is desired, and the other signal is filtered out of the output of the mixer.

  6. Wavelength - Wikipedia

    en.wikipedia.org/wiki/Wavelength

    The wavelength of a sine wave, λ, can be measured between any two points with the same phase, such as between crests (on top), or troughs (on bottom), or corresponding zero crossings as shown. In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats.

  7. Electromagnetic spectrum - Wikipedia

    en.wikipedia.org/wiki/Electromagnetic_spectrum

    However, there are certain wavelength ranges ("windows") within the opaque range that allow partial transmission, and can be used for astronomy. The wavelength range from approximately 200 μm up to a few mm is often referred to as Submillimetre astronomy, reserving far infrared for wavelengths below 200 μm.

  8. Rydberg–Ritz combination principle - Wikipedia

    en.wikipedia.org/wiki/Rydberg–Ritz_combination...

    Also, a transition from an initial to a final energy level involves the same energy change whether it occurs in a single step or in two steps via an intermediate state. The energy of transition in a single step is the sum of the energies of transition in two steps: (E 3 – E 1) = (E 2 – E 1) + (E 3 – E 2).

  9. Bragg's law - Wikipedia

    en.wikipedia.org/wiki/Bragg's_law

    Bragg diffraction [9]: 16 Two beams with identical wavelength and phase approach a crystalline solid and are scattered off two different atoms within it. The lower beam traverses an extra length of 2dsinθ. Constructive interference occurs when this length is equal to an integer multiple of the wavelength of the radiation.