Second harmonic generation (SHG) method is an official moisture content determination technique that involves irradiating a material with a laser beam and observing the second harmonic (SH) light that is generated. This SH light is a result of the material’s nonlinear optical response to the laser beam.
The procedure involves shining a laser beam of known wavelength and polarization at the material sample. The SH light generated by the material is then collected and measured. The intensity of the SH light is proportional to the square of the moisture content in the material. This relationship can be used to determine the moisture content of the material.
* Non-destructive: The SHG method does not require any physical contact with the material sample, making it a non-destructive method.
* Rapid: The SHG method is a very rapid method, providing results in a matter of seconds.
* Accurate: The SHG method is a highly accurate method, with accuracies of up to 0.1% being reported.
* Versatile: The SHG method can be used to measure the moisture content of a wide range of materials, including paper, wood, textiles, and food.
* Line of sight: The SHG method requires the laser beam to directly strike the material sample, which may not be possible for all situations.
* Texture: The texture of the material sample can affect the accuracy of the SHG method, as it can alter the interaction between the laser beam and the material.
* Moisture distribution: The SHG method only measures the moisture content at the surface of the material sample, which may not be representative of the moisture content throughout the entire material.
The SHG method is a valuable tool for moisture content determination. Its advantages include its non-destructive nature, speed, accuracy, and versatility. However, its limitations, such as the need for line of sight, sensitivity to texture, and inability to measure moisture content throughout the entire material, must be considered when choosing this method.