## Help

### Here you find a few instructions and hints

On this page you can easily convert between the different ways to quantify spectral characteristics of waves. Conversions take place between wavelength, wavenumber, frequency, and energy. For your information also the maximal coherence length and the coherence time will be calculated if two waves are given.

Please enter the wavelength, wavenumber, frequency, or energy of a wave into one of the two fields, choose the physical unit (take care of the order of magnitude and the unit!) and push the enter key or one of the "calculate" buttons. Instantaneously all possible variants to quantify this kind of light will be given.

If you are interested in the spectral distance to a second wave, you may enter a second wave into the second field or alternatively pick and enter a relative distance. Again, upon pressing the enter key or the "calculate" button the conversion will be performed.

These calculations can be performed in different media. You can chose via the drop-down menu for the index of refraction. Two indices are predefined: n=1 for vacuum and n=1.000292 for air under normal conditions. If you pick "manually" you may enter you own arbitrary index of refraction into the field next to the menu.

The conversions are based upon the following formulae:

- E=h*f in units of Electronvolts [eV]
- k
_{chem}=1/λ in inverse units of length [cm^{-1}] - k
_{phys}=2π/λ in inverse units of length [m^{-1}] - f=c*k in Hertz [Hz]
- Coherence time: τ= 1/πΔf (Details)
- Coherence length: L
_{coh}= c*τ

**Attention:** Please note that the variant k=1/λ is common for spectroscopy. The variant k=2π/λ mostly used in physics differs by a factor of 2π.

Here, both are given. For a distinction the "spectroscopic" variant will carry the unit cm^{-1} which is not really common anymore in physics. The "physical" variant will carry the unit m^{-1}.

If the input fields carry a correct unit for their values ("m", "Hz", "eV", or for the wavenumber "cm1" or "icm") and possibly an SI-prefix for the decade (a=10^{-15}, f, p, n, ?=y=u, m, 1, k, M, G, T, P=10^{15}), the corresponding drop-down menu will be fully ignored (and later on adapted).

For instance enter "990.778 GHz" or "1.23 keV" into one of the fields. Spaces will be ignored and now also the technical notation "1.2e-6m" be accepted.

If the input contains a capital "D" then the second input will be interpreted as a differential value.

If, for instance, the first wave reads "1000.1 THz" then the following inputs for the second wave will be equivalent: "-100 GHzD", "D -0.1 THz", "1000 THz", "1PHz" etc.

For a distinction of the "spectroscopic" and the "physical" wavenumber, if the unit for the input is given as icm or cm1 it is considered "spectroscopic" and otherwise for im or m1 it is considered "physical".

If you like to enter values directly or have them calculated by scrips you can also modify the address line as e.g."http://.../?typn=nv&n=1&typ1=wellep&typ2=lambda&wert1=1064nm&wert2=1064.5nm"

We happily receive feedback regarding this page!

Do you experience problems, do you have comments or suggestions, or did you even find a bug? Please let us know.