The new nonlinear optical (NLO) crystal BaGa4S7 for the mid-infrared (IR) has been grown by a Bridgman-Stockbarger technique. Polycrystalline materials with stoichiometric composition were synthesized from BaS, Ga, and S as the initial materials by solid-state reactions. The ultraviolet (UV) and IR transmittance of the crystal was determined with polished crystal pieces. The UV and IR optical absorption edges were found to be at 350 nm and 13.7 μm, respectively. From optical measurements of second harmonic generation on powders, the NLO coefficient d 33 was determined to be 12.6 pm/V. The laser damage threshold of a single crystal reached about 1.2 J/cm2 at 1.064 μm. The Vickers-hardness value of the crystal is 327.5 HV5, which is equivalent to Mohs’ hardness of about 5.

Current image captioning methods are usually trained via (penalized) maximum likelihood estimation. However, the log-likelihood score of a caption does not correlate well with human assessments of quality. Standard syntactic evaluation metrics, such as BLEU, METEOR and ROUGE, are also not well correlated. The newer SPICE and CIDEr metrics are better correlated, but have traditionally been hard to optimize for. In this paper, we show how to use a policy gradient (PG) method to directly optimize a linear combination of SPICE and CIDEr (a combination we call SPIDEr): the SPICE score ensures our captions are semantically faithful to the image, while CIDEr score ensures our captions are syntactically fluent. The PG method we propose improves on the prior MIXER approach, by using Monte Carlo rollouts instead of mixing MLE training with PG. We show empirically that our algorithm leads to easier optimization and improved results compared to MIXER. Finally, we show that using our PG method we can optimize any of the metrics, including the proposed SPIDEr metric which results in image captions that are strongly preferred by human raters compared to captions generated by the same model but trained to optimize MLE or the COCO metrics.

A new series of alkaline beryllium borates NaBeB(3)O(6), alpha-KBe(2)B(3)O(7), beta-KBe(2)B(3)O(7), gamma-KBe(2)B(3)O(7), and RbBe(2)B(3)O(7) were synthesized by spontaneous crystallization with molten fluxes based on A(2)O-B(2)O(3) (A = Na, K, Rb) solvent. For KBe(2)B(3)O(7), three polymorphous phases were found and are referred to as alpha-, beta-, and gamma-KBe(2)B(3)O(7) relative to their crystallization temperature from high to low. All of the materials are noncentrosymmetric except alpha-KBe(2)B(3)O(7). NaBeB(3)O(6) and alpha-KBe(2)B(3)O(7) consist of a new anionic group [Be(2)B(3)O(11)](9-), which is similar to a naphthalene molecule that is rarely found in inorganic matter. beta-KBe(2)B(3)O(7), gamma-KBe(2)B(3)O(7), and RbBe(2)B(3)O(7) consist of 2D alveolate beryllium borate layers [Be(2)BO(5)](infinity), which are connected by strong covalent bonds. The UV-vis diffuse reflectance spectroscopy on powder samples indicated that the short-wavelength absorption edges of noncentrosymmetric materials are all below 200 nm. Second-harmonic generation (SHG) on powder samples was measured using the Kurtz and Perry technique, which indicated that NaBeB(3)O(6), beta-KBe(2)B(3)O(7), gamma-KBe(2)B(3)O(7), and RbBe(2)B(3)O(7) are all phase matchable materials, and their measured SHG coefficients were approximately 1.60, 0.75, 0.68, and 0.79 times as large as that of d(36) (KDP), respectively.

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A novel mixed alkali hydro-isocyanurate, KLi­(HC3N3O3)·2H2O was first prepared in AOH-BOH-H3C3N3O3 (A/B = Li/Na/K/Rb/Cs) system via a solvent-drop grinding method. KLi­(HC3N3O3)·2H2O shows a large second harmonic generation response (5.3 × KH2PO4) with an ultraviolet cutoff edge of 237 nm. More importantly, the bulk single crystal can be readily grown through water solution technique. Characterization of these crystals indicates that KLi­(HC3N3O3)·2H2O has a high laser damage threshold (LDT) (4.76 GW/cm2) and exhibits a large birefringence (Δn = 0.186@514 nm), which reduces Type I phase-matching to 246 nm.

The nonlinear optical crystal KBe2BO3F2 has been used to produce vacuum ultraviolet second-harmonic generation with an output range of 200–184.7 nm. The Sellmeier equation further indicates that this new crystal can generate the sixth harmonic from Nd-based laser systems.

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A scientifically valid test process to measure polycrystalline birefringence was proposed and confirmed as an effective method for screening anisotropic microcrystals.