Refractive index database

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Optical constants of KH2PO4 (Potassium dihydrogen phosphate, KDP)
Zernike et al. 1964: n(o) 0.214–1.53 µm

Wavelength: µm

Complex refractive index (n+ik)[ i ]

n   k   LogX   LogY   eV

Derived optical constants

Dispersion formula [ i ]



24.8 °C. Ordinary ray (o).


F. Zernike, Jr. Refractive Indices of Ammonium Dihydrogen Phosphate and Potassium Dihydrogen Phosphate between 2000 Å and 1.5 µ, J. Opt. Soc. Am. 54, 1215-1219 (1964). Cited in Handbook of Optics, 3rd edition, Vol. 4. McGraw-Hill 2009.


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Potassium dihydrogen phosphate, KH2PO4 (KDP)

Potassium dihydrogen phosphate, commonly known as KDP (KH2PO4), is a widely used nonlinear optical crystal, especially esteemed for its applications in laser technology. It serves as an efficient frequency converter and is often deployed for second and third harmonic generation, as well as for electro-optical modulation. KDP's transparency range is quite broad, extending from the ultraviolet to the infrared spectrum. Another advantage of this material is its relatively low cost and ease of large-scale production, which makes it particularly useful for high-power laser systems. It does, however, have lower damage thresholds compared to some other nonlinear optical materials. KDP is also hygroscopic, requiring careful handling to prevent moisture-related degradation. Overall, KDP remains a cornerstone material in nonlinear optics and laser science.

Other names

  • Monopotassium phosphate
  • Monobasic potassium phosphate (MKP)

External links