Single crystals of L‐alanine have been grown from buffered aqueous solutions and characterised as to their optical quality via wavefront distortion analysis, electrooptical response and harmonic ...generation efficiency. Refraction indices as well as phase matching loci were found in satisfactory agreement with previously published data for crystals grown in non buffered solution. Estimates for the electro‐optical response are reported for the first time. The experimentally observed crystal habit is discussed in terms of morphological importance (M.I.), which was found to be in disagreement with the predictions of crystallographic criteria based on the interplanar distance dhkl, on the periodic bond chains (PBC) and the attachment energy Eatt. This disagreement is tentatively attributed to the presence of impurities and non‐appropriate supersaturation conditions.
Looking for compounds with optical properties comparable or better than those of urea we have performed crystallization tests on phenylurea, 1,1-dimethylurea and 1,3-dimethylurea. Appreciable results ...have been obtained for 1,3-dimethylurea grown by the normal freezing method. The ingots display good keeping and mechanical properties. Phase matching has been achieved with an encouraging doubling efficiency.
Urea is an excellent nonlinear optical (NLO) medium. However, growth of large high-quality crystals for practical use still remains a challenge due to its unfavourable growth properties. Improved ...crystalline and optical quality could be expected in derivatives of urea. In this contribution we report on the growth of urea and its derivatives: monomethylurea (NMU), 1,1-dimethylurea (1,1-DMU), and 1,3-dimethylurea (1,3-DMU). Satisfactory quality and reasonable size of both urea and monomethylurea crystals have been achieved. Some evaluation of the quality of the grown crystals is reported. This work shows that NMU exhibits a better crystal habit than urea does, while preserving almost the same transparency window. This would suggest that NMU is a potentially promising material in nonlinear optical applications.
Monomethylurea (NMU), a methyl derivative of urea, has been focused recently as promising nonlinear optics (NLO) material. We grew NMU using long thin seeds capped at both ends. This kind of growth ...was successful, and gave crystals of high structural and optical quality. However, the useful cross section was limited due to the presence of a defected region surrounding the seed. For this reason, we tested an alternative growth method by which larger (25 × 25 mm) cross sections have been obtained. Here we report on this growth procedure, on morphological studies, and on some linear and nonlinear optical characterizations.
It was previously reported on the growth of monomethylurea (NMU) single crystals from methanol solution by a mechanical limitation‐direction (MLD) technique in which long (100) oriented seeds, capped ...on their extremities, were employed. The crystals obtained by this technique, in spite of their good structural and optical quality, presented their core region, in which the seed was located, with a higher density of structural defects and henceforth a reduced cross section useful for optical applications. It is here referred to a new, top‐seeded growth configuration, devised on the basis of a preliminary PBC analysis for assessing the morphological importance of the crystal faces experimentally observed during crystal growth, which allows to grow NMU crystals in which the defected core region is removed for almost the entire length of the crystal.
A new growth method, based on a vapour‐liquid‐solid (VLS) mechanism, is reported for preparing single crystals of N‐methylurea (NMU), a material which appears to be a good alternative to urea for ...non‐linear optical applications in the “near UV‐visible” region of the spectrum. Details of the growth procedure are given and it is shown that large single crystals, with volumes up to 7 ÷ 10 cm3, can be obtained with satisfactory reproducibility and very fast growth rate. Structural and optical characterisation, still preliminary, are reported, which evidence a crystalline quality comparable to that of urea and N‐methylurea as previously grown with other growth techniques. Cryst. Res. Technol., Vol. 32, No. 1.
