Ammonium dihydrogen phosphate NH4H2PO4 ADP

Ammonium dihydrogen phosphate, with the chemical formula NH₄H₂PO ₄, is commonly referred to as ADP. It is an important artificially grown water-soluble crystal, on par with its "brother" potassium dihydrogen phosphate, and is an indispensable functional material in the field of optoelectronics.

ADP crystals belong to the tetragonal crystal system and have excellent nonlinear optical and electro-optic effects, which make them play a key role in multiple high-tech fields.

1、 Main application scope

The application of ADP crystals mainly focuses on utilizing their unique optical and electrical properties.

1) Nonlinear Optics Field - Laser Frequency Conversion

This is one of the core applications of ADP. When high-intensity laser passes through ADP crystal, the crystal can change the frequency of the laser and output a new wavelength of laser.

Doubling: Doubling the frequency of the incident laser (halving the wavelength). For example, converting 1064nm infrared laser into 532nm green laser. This is the most common application.

Sum frequency and difference frequency: Mix two lasers of different frequencies to produce a third laser with a frequency equal to their sum or difference.

Application scenarios: Used in scientific research, industrial processing, medical (such as laser therapy), military (such as LiDAR), and other systems that require specific wavelength lasers.

2) Electro optic modulation field

Under the action of an external electric field, the refractive index of ADP crystals will change (i.e., the electro-optic effect). By utilizing this characteristic, various devices for controlling lasers can be produced.

Electro optic modulator: precise control of laser intensity, phase, or polarization state through electrical signals. This is a core component in high-speed optical communication, laser printing, and display technology.

Q-switch: A "switch" used to generate high-energy, short pulse lasers. ADP crystals can be used as Q-switches in pulsed lasers.

3) X-ray and nuclear technology field

X-ray spectroscopic crystal: The lattice constant of ADP crystal matches well with the wavelength range of X-rays, and can monochromatize X-rays like a "grating" (separating X-rays of specific wavelengths). Widely used in scientific research and industrial equipment such as X-ray fluorescence analyzers and X-ray diffractometers.

Cherenkov radiation: ADP crystals can be used to detect high-speed charged particles in high-energy physics experiments.

4) Piezoelectric application field

ADP crystals also exhibit piezoelectric effects, which generate electrical signals under mechanical pressure. Although not as widely used as quartz crystals in this regard, they are still used in certain specific sensors and transducers.

2、 Performance advantages

Compared with similar materials (especially its close relative KDP crystal), ADP crystal has the following significant advantages and characteristics:

1) High laser damage threshold

ADP crystals can withstand high power laser irradiation without being damaged. This is crucial for high-power laser systems, ensuring the stability and lifespan of the device in harsh environments.

2) Excellent UV transmittance performance

ADP crystals have high transmittance in the ultraviolet spectral region, typically ranging from about 180nm (vacuum ultraviolet) to about 1200nm (infrared). This makes it particularly suitable for nonlinear optical and electro-optical applications that generate or manipulate ultraviolet lasers, which is an advantage that many other crystals do not possess.

3) Moderate nonlinear optical and electro-optic coefficients

Although ADP's nonlinear optical and electro-optic coefficients are not the highest, it is at a "sufficient and balanced" level, combined with its other excellent properties such as high damage threshold and UV transmittance, making it a very reliable and practical choice.

4) Easy to grow large, high optical quality single crystals

ADP crystals can be relatively easily grown into high-quality single crystals with large size, high optical uniformity, and few internal defects through aqueous solution method. This is very advantageous for industrial production and manufacturing of large optical components, as it can effectively control costs.

5) Stable physical and chemical properties

ADP crystals have moderate hardness and are easy to cut, grind, and polish. Its chemical properties are also relatively stable, making it easy to store and use.