Bruce G. Tiemann

The Effect of varying Ground-state Aromaticity on the First Molecular Electronic Hyperpolarizabilites of Organic Donor-Acceptor Molecules

A series of compounds of the form 4-dimethylaminophenyl–polyene–acceptor, where the polyene ranges from nothing to all-trans-1,3,5-hexatriene and the acceptor is 2-nitrovinyl, formyl, or 2,2-dicyanovinyl has been prepared and their β values measured by solution electric-field-induced second-harmonic generation; these molecules, which lose only one aromatic resonance upon charge-transfer excitation, show enhanced β compared to bi-aromatic molecules with the same substitution and total conjugation length, such as 4-dimethylamino-4′-nitrostilbene (DANS), a well-known benchmark for high β organic molecules.

20-W and 50-W solid-state sodium beacon guidestar laser systems for the Keck I and Gemini South telescopes

Lockheed Martin Coherent Technologies (LMCT) is developing 20 W and 50 W commercial solid-state sodium beacon Guidestar Laser Systems (GLS) for the Keck I and Gemini South telescopes, respectively. This work represents a critical step toward addressing the need of the astronomical adaptive optics (AO) community for a standardized, robust, turn-key, commercial GLS that can be configured for different observatory facilities and for different AO formats - including multi-conjugate AO (MCAO) and future extremely large telescopes. These modular systems build on the proven laser technologies, user-friendly interface, and low maintenance design that were developed for the successful 12 W GLS delivered by LMCT to the Gemini North telescope in February 2005. This paper describes the GLS requirements for the Keck I and Gemini South telescopes, the design of the laser oscillators, amplifiers, sum-frequency generator, and diagnostics; the functionality of the automated remote laser control system; size, weight, power, and performance data; and the current status of the programs.

20 W and 50 W Guidestar Laser System Update for the Keck I and Gemini South Telescopes

Lockheed Martin Coherent Technologies has developed 20 W and 50 W commercial solid-state sodium beacon Guidestar Laser Systems (GLS) for the Keck I and Gemini South telescopes, respectively. This work represents a critical step toward addressing the need of the astronomical adaptive optics (AO) community, including multi-conjugate AO and AO tomography for future extremely large telescopes. This paper describes the status of GLS for the Keck I and Gemini South telescopes. The design and experimental results of the laser oscillators, amplifiers and sum-frequency generator will be discussed.

System overview of 30 W and 55 W sodium guide star laser systems

We report on the successful delivery of a 30 W solid-state sodium Guide Star Laser System (GLS) to the W. M. Keck Observatory in 2009, and the demonstration of a 55 W GLS delivered to the Gemini South Observatory in 2010. This paper describes the GLS performance results of both the Keck I and Gemini South GLSs with an emphasis on the system design and delivered performance. The 589 nm output was generated via Sum Frequency Mixing (SFM) of 1064 nm and 1319 nm Nd:YAG lasers in a LBO (Lithium Triborate) nonlinear crystal. The Keck GLS underwent extensive testing and has demonstrated consistent performance with a CW mode-locked output of > 30 W and measured beam quality of M2 < 1.2 while locked to the sodium D2a transition. The Keck GLS was installed on the telescope in late 2009 and first light on the sky was achieved in early 2010. Factory testing of the Gemini South GLS shows a CW modelocked output of > 55 W and measured M2 ~1.2 while locked to the sodium D2a line center. The Gemini South GLS has produced a maximum power of 76 W at 589 nm with 85 W of 1319 nm and 110 W of 1064 nm as inputs to the SFM, representing a single-pass conversion efficiency of 39%.

The dependence of the molecular first hyperpolarizabilities of merocyanines on ground-state polarization and length

We report here the dipole moment (µ) and first hyperpolarizability (β) determined by electric field-induced second harmonic generation, for several merocyanine dyes containing an 1,3,3-trimethylindoline heterocycle as a ‘donor’ in which the ‘acceptor’ end of the molecule and the polyene bridge length was systematically varied; dyes with hexamethine bridges gave positive β, while that with a dimethine bridge gave a negative β value.

Synthesis and first hyperpolarizabilities of acceptor-substituted β-apo-8′-carotenal derived compounds

The synthesis and second-order nonlinear optical properties of acceptor-substituted biologically derived β-apo-8′-carotenal compounds are reported; electric field-induced second harmonic generation (EFISH) measurements give values of β(0) which are 2–6 times greater than for 4-N,N-dimethylamino-4′-nitrostilbene (DANS).

Experimental demonstration of the relationship between the second- and third-order polarizabilities of conjugated donor-acceptor molecules

The dependence of the second- and third-order polarizabilities ((beta) and (gamma) ) on ground-state polarization was measured for a series of donor-acceptor polyenes using electric field induced second harmonic generation and third harmonic generation, respectively. The changes in ground-state polarization, associated with the donor/acceptor strength or solvent polarity, were probed by x-ray crystallography, 1H-NMR, electronic absorption, and Raman spectroscopies. The observed behavior of (beta) and (gamma) as a function of ground- state polarization agrees well with theoretical predictions. In particular, positive and negative peaks, as well as sign changes, were observed for both (beta) and (gamma) . The dependences for (beta) and (gamma) are consistent with a derivative relationship between them. In addition, the third-order polarizability of a series of molecules possessing zero bond length alternation was found to be negative, in agreement with predictions based on the relationship between the polarizabilities and ground-state geometry.

The first molecular electronic hyperpolarizabilities of highly polarizable organic molecules : 2,6-di-tert-butylindoanilines

The first molecular hyperpolarizabilities (β) of a series of 2,6-di-tert-butylindoanilines, measured by electric-field-induced second harmonic generation are somewhat more sensitive to donor strength than was found for analogously substituted nitrostilbenes, and dimethylindoaniline has a β roughly twice that of its 2,6 di-tert-butylated analogue, measured in chloroform; solvatochromic measurements on the former compound suggest that this decrease in hyperpolarizability is consistent with a bound-solvent effect.

Structure/property relationships for molecular second-order nonlinear optics

Using a two-state model, it was recently shown that there is an optimal combination of donor and acceptor strengths for a given bridge that will maximize the first molecular electronic hyperpolarizability ((beta) ). To date, molecules with sufficiently strong donors and acceptors have not been synthesized to reach this ideal point. Here we outline synthetic strategies that lead to molecules where (beta) is optimized by tuning the degree of bond alternation in the (pi) -electron system between the donor and acceptor. Implementation of this strategy relies on the realization that molecules with strongly aromatic end groups will not have the correct balance of two limiting charge transfer resonance forms in the ground state to achieve the degree of bond alternation required to optimize the molecular hyperpolarizability. Electric field induced second harmonic generation studies on organic molecules with various bridge structures support our hypothesis.