Investigation on Improving ADP Crystals’ Thermal Stability for Noncritical Phase‐Matching Fourth Harmonic Generation Application

Abstract

Ammonium dihydrogen phosphate (ADP) crystals have higher fourth harmonic generation (FHG) efficiency than deuterated potassium dihydrogen phosphate (DKDP) crystals, because of the higher nonlinear optical coefficient. However, the narrower full-width at half-maximum (FWHM) temperature bandwidth and poor thermal stability limited the application in the noncritical phase-matching (NCPM) FHG. In this article, ADP and a series of deuterated ADP (DADP) crystals are grown through point-seed rapid growth method to investigate a feasible experimental condition on improving ADP crystals' thermal stability for NCPM FHG application. The deuterium doping experiment results indicate that the 60% DADP crystal could accommodate more laser-induced heat capacity during FHG processing and could achieve higher FHG output, but with poor thermal stability. Therefore, 60% DADP crystal's FHG stability measured by air indirect heating method. About 7% more stable FHG output is obtained than direct heating by copper, which is more suitable for FHG stability of ADP/DADP crystals.

Homogeneity of large rapidly grown ADP crystals

“…Angular acceptance and temperature acceptance are critical parameters for frequency multiplication materials for NCPM FHG. Previous studies based on the NCPM FHG in ADP crystals could give estimation of external angular bandwidth of ADP is 50.5 mrad·cm 1/2 , which corresponds to an angular phase-mismatch sensitivity, ∂κ/Δ2Θ, of 4.36×10 −3 mrad −2 ·cm −1 [29]. This value is superior to those in a rapid growth DKDP crystal.…”

Study on defects during Fe3+ doping and annealing in ADP crystals

“…Thus, research institutions worldwide are dedicated to enhancing the performance of ADP crystals to expand their applications in higher harmonic generation. [6][7][8] The growth of ADP crystals typically employs the "point-seed crystal" method, which offers faster growth rates and improved crystal quality compared to traditional large cross-section slice seed methods. 9,10 To further optimize crystal quality, researchers adjust key growth parameters, such as incorporating organic (e.g., amino acids and dyes) and inorganic (e.g., metal ions) additives, to enhance the optical and dielectric properties of ADP crystals.…”

“…Thus, research institutions worldwide are dedicated to enhancing the performance of ADP crystals to expand their applications in higher harmonic generation. 6–8…”