The refractive index of a material generally varies with respect to wavelength, a phenomenon known as dispersion.
The way light interacts with a material, including how much it bends (refractive index), depends on the wavelength of the light.
Normal Dispersion
In most common situations, particularly in regions of the spectrum where the material does not absorb light, the relationship between refractive index and wavelength follows a predictable pattern:
- The refractive index tends to decrease with increasing wavelength.
- This means that shorter wavelengths (like blue light) are bent more than longer wavelengths (like red light) when passing through the material.
- Conversely, the refractive index tends to increase with frequency, as frequency and wavelength are inversely related.
This behavior is referred to as "normal dispersion".
Anomalous Dispersion
While normal dispersion is typical, there are situations, often near wavelengths where the material does absorb light strongly, where the behavior is different. This is called "anomalous dispersion":
- Anomalous dispersion is in contrast to normal dispersion.
- In regions of anomalous dispersion, the refractive index increases with wavelength.
Key Takeaways
- The variation of refractive index with wavelength is called dispersion.
- Normal dispersion (most common in non-absorbing regions): Refractive index decreases as wavelength increases.
- Anomalous dispersion: Refractive index increases as wavelength increases, typically near absorption bands.
