What Is Wavelength Standard? Advantages Of Wavelength Standards and Disadvantages of Material Standards

In the line and end standard, the working standard is derived by successive comparison of a physical standard. This may lead to an unacceptable error of the standard itself. The dependency of working standard on physical standard is eliminated by using wavelength of monochromatic radiation as a natural and invariable unit of length. By doing so, the definition of standard length relative to the meter is expressed in terms of the accurately known wavelength of light.

The wavelength produced by the element depends on the amount of isotope impurity present in the standard. So the pure isotopes of natural element, Krypton 86, is considered the most suitable source of pure monochromatic light (if used in hot cathode discharge lamp maintained at 68K). Using wavelength standard, the meter is defined as the 1650763.73 x wavelength of a Krypton86 atom in a vacuum. Since it is not physical, there is no need to preserve the wavelength standard. This standard length is reproducible, and replication error can be of the order of 1 parts in 10⁹. It's accessible to any laboratory.

The modern meter is defined as the length of the path travelled by the light in a vacuum in a time interval of 1/299792458 seconds. This is more accurate than the standard using Krypton-86. Here accuracy is about 3 parts in 10¹¹.

🔗Difference between line standard and end standard in metrology

Comparison between material standard and wavelength standard in metrology

What are the disadvantages of material standards?

1. It is difficult to reproduce the material standard.
2. Material standards are subjected to ageing. Environmental factors like temperature, pressure, humidity, etc. also affected them., resulting in variations in length.
3. Difficulty while comparing and verifying the size of the gauge.
4. The material standards must have appropriate protection to avoid damage. So, the preservation of material standards is challenging.
5. The replicas of the standard are not available for use in other places.
6. A conversion factor is necessary for changing the material standards to metric systems.

Advantages of wavelength standard

1. It virtually independent of the ambient conditions such as temperature, pressure and humidity
2. Not subjected to wear and tear. 
3. Readily available in laboratories and industries.
4. Comparing and verifying the standard is simplified.
5. When compared to material standard, wavelength standard ensures higher accuracy.
6. Wavelength standard is easily and accurately reproducible.
7. It can easily transfer into other standards.
8. Since wavelength standard is not physical, there is no need for preservation. There is no fear of being destroyed.