Frequency-upconverted Lasing Research Articles

Manipulating four-photon absorption of ZnO via Ga doping.

Multi-photon absorption in the second near-infrared (NIR-II) regime has attracted extensive attention due to biological imaging and frequency-upconverted lasing applications. We report the dispersion of four-photon absorption (4 PA) response in pristine and Ga-doped ZnO single crystals over the spectral range 1180-1350 nm. Femtosecond Z-scan results demonstrate that Ga doping can significantly enhance the 4 PA coefficient β4 of ZnO. Interestingly, the wavelength dependency of β4 in Ga-doped ZnO shows a strong resonance around 1215-1250 nm, which is correlated with the PL peak of Ga-doped ZnO at 405 nm. Femtosecond pump-probe measurements validate that Ga doping has no profound impact on the ultrafast carrier relaxation of ZnO, indicating Ga doping leads to a shallow state rather than a deep trap within the bandgap. The possible mechanism of 4 PA enhancement induced by degeneracy with multi-photon absorption resonance to the Ga-doped state is discussed. Our results verify the strong potential of Ga-doped ZnO with tunable nonlinear optical properties as a promising candidate for nonlinear optical and nanophotonic devices in the NIR-II region.

Stable and enhanced frequency up-converted lasing from CsPbBr3 quantum dots embedded in silica sphere.

Perovskites have emerged as a class of cutting-edge light-emitting materials; however, their poor stability, due to the high sensitivity to moisture in the ambient environment, severely hinders their further application. Here, to obtain stable perovskite-based laser with excellent optical performance, all-inorganic perovskite CsPbBr3 quantum dots (QDs) evenly distributed into sub-micro silica sphere (CsPbBr3-SiO2) have been used as laser gain medium. The single silica sphere embedded by plentiful CsPbBr3 QDs demonstrates frequency up-converted lasing with compounded mode of random and whispering-gallery-mode (WGM) at room temperature. Furthermore, by incorporating the CsPbBr3-SiO2 spheres into a microtubule, the frequency up-converted WGM lasing has been successfully achieved under two-photon excitation. Notably, the CsPbBr3-SiO2 microtubule resonator exhibits a low lasing threshold of 430 μJ/cm2, mostly due to the enhanced gain for CsPbBr3 QDs inside the silica sphere. Moreover, stable WGM lasing is observed under continuous optical pump for 140 min, benefited from the protection of silica shells, which isolate the QDs from the environmental conditions. The enhanced lasing performance provides an effective way for further exploration and application of perovskite-based micro/nano photonic devices.

Multiphoton harvesting metal-organic frameworks.

Multiphoton upconversion is a process where two or more photons are absorbed simultaneously to excite an electron to an excited state and, subsequently, the relaxation of electron gives rise to the emission of a photon with frequency greater than those of the absorbed photons. Materials possessing such property attracted attention due to applications in biological imaging, photodynamic therapy, three-dimensional optical data storage, frequency-upconverted lasing and optical power limiting. Here we report four-photon upconversion in metal–organic frameworks containing the ligand, trans, trans-9,10-bis(4-pyridylethenyl)anthracene. The ligand has a symmetrical acceptor–π–donor–π–acceptor structure and a singlet biradical electronic ground state, which boosted its multiphoton absorption cross-sections. We demonstrate that the upconversion efficiency can be enhanced by Förster resonance energy transfer within host–guest metal–organic frameworks consisting of encapsulated high quantum yielding guest molecules. Using these strategies, metal–organic framework materials, which can exhibit frequency-upconverted photoluminescence excited by simultaneous multiphoton absorption, can be rationally designed and synthesized.

Upconversion Lasers: Stable and Low‐Threshold Optical Gain in CdSe/CdS Quantum Dots: An All‐Colloidal Frequency Up‐Converted Laser (Adv. Mater. 17/2015)

An all-colloidal vertical-cavity surface-emitting laser (VCSEL) is reported by C. Dang, H. Sun, H. V. Demir and co-workers on page 2741, which offers high performance and stability while being fully solution processed. This all-colloidal laser is based on a stacked architecture of dielectric mirrors, based on metal oxide nanoparticles sandwiching semiconductor nanocrystals as the optical gain medium, forming an all-solution-processed VCSEL structure. Here, using tailored core-shell quantum dots that have suppressed non-radiative Auger recombination enables the achievement of sub-mJ cm−2 frequency up-converted lasing thresholds, which make these all-colloidal devices highly promising for optoelectronic and biomedical applications.

Multiphoton Excited Fluorescent Materials for Frequency Upconversion Emission and Fluorescent Probes

Recent progress in developing various strategies for exploiting efficient MPA fluorophores for two emerging technological MPA applications including frequency upconversion photoluminescence and lasing as well as 2PA fluorescence bioimaging and biosensing are presented. An intriguing application of MPA frequency-upconverted lasing offers opportunity for the fabrication of high-energy coherent light sources in the blue region which could create new advantages and breakthroughs in various laser-based applications. In addition, multiphoton excitation has led to considerable progress in the development of advanced diagnostic and therapeutic treatments; further advancement is anticipated with the emergence of various versatile 2PA fluorescence probes. It is widely appreciated that the two-photon excitation offers significant advantages for the biological fluorescence imaging and sensing which includes higher spatial resolution, less photobleaching and photodamage as well as deeper tissue penetration as compared to the one-photon excited microscopy. To be practically useful, the 2PA fluorescent probes for biological applications are required to have a site-specificity, a high fluorescence quantum yield, proper two-photon excitation and subsequent emission wavelengths, good photodecomposition stability, water solubility, and biocompatibility besides large 2PA action cross-sections.

Frequency up-converted lasing in polymeric composites with two-photon absorbing antenna

Energy-transfer-coupled polymeric composites with donors of two-absorbing dyes and acceptors of polymer gain medium are introduced for up-converted laser applications. The two-photon pumped hybrid polymer lasers show significant performance improvement with nearly 10 times reduction of lasing threshold and over 100 times extension of lifespan.

Highly Efficient Multiphoton‐Absorbing Quadrupolar Oligomers for Frequency Upconversion

Two series of quadrupolar diphenylamino-endcapped oligofluorenes, PhN-OF(n)-NPh (n=2-5) and PhN-OF(n)-TAZ-OF(n)-NPh (n=1-4), which have an electron-withdrawing 1,2,4-triazole (TAZ) moiety as central core, with D-π-A-π-D structural motif (D=donor, A=acceptor), have been synthesized by palladium-catalyzed Suzuki cross-coupling of 9,9-dibutyl-7-(diphenylamino)-2-fluorenylboronic acid and the corresponding (1,2,4-triazole-based) aryl halide as key step. On pumping with infrared femtosecond lasers, these oligomers showed very strong multiphoton-excited blue photoluminescence. These D-π-D and D-π-A-π-D quadrupolar oligofluorenes exhibit superior three-photon absorption properties compared to the respective D-π-A counterparts with a highest three-photon absorption cross-section (σ(3)) of up to 2.72×10(-77) cm(6) s(2) . Despite the comparable linear and multiphoton absorption properties of the two types of quadrupolar oligomers PhN-OF(n)-NPh and PhN-OF(n)-TAZ-OF(n)-NPh, only the former exhibit remarkably intense and highly efficient multiphoton-excited frequency-upconverted deep blue lasing, which gives rise to record high lasing efficiency of 0.097% and very narrow of full width at half-maximum of the lasing spectra. Our findings suggest that quadrupolar-type molecules/oligomers are superior for multiphoton excited frequency upconverted lasing to their dipolar counterparts and also provide important guidelines to design highly efficient three-photon absorption molecules for photoluminescence and lasing applications.

Frequency upconverted lasing of nanocrystal quantum dots in microbeads

Stable, frequency upconverted lasing of semiconductor nanocrystal quantum dots was demonstrated in silica microbeads under two-photon pumping conditions. Upon infrared excitation, the stimulated emission of the nanocrystal-doped microbeads exhibits sharp peaks at λ∼610 nm with narrow line widths of ≤1 nm. The lasing action has been attributed to the biexciton gain coupled to the whispering gallery modes in spherical cavities, as confirmed by time-resolved photoluminescence spectra. The lasing lifetime characterized in term of pulse numbers (∼106 pulses) was two orders of magnitude longer than that of the dye salt-based two-photon lasers.

Frequency-upconverted whispering-gallery-mode lasing in ZnO hexagonal nanodisks

Low threshold, frequency-upconverted lasing in the two-photon absorption regime was observed in hexagonal ZnO nanodisks. Upon near-IR excitation, the ZnO nanodisk resonators produced UV laser emission with a remarkably low threshold (approximately 1 mJ/cm(2)) as well as a resolved lasing linewidth of approximately 0.1 nm. Modal analysis and far-field photoluminescence imaging of the nanolasers have suggested the dominance of whispering-gallery modes in the two-photon pumped microcavity lasing process.

Frequency Up-Converted Lasing of Nanocrystal Quantum-Dots in Microbeads

not Available.

Design, crystal structures and enhanced frequency-upconverted lasing efficiencies of a new series of dyes from hybrid of inorganic polymers and organic chromophores

A new series of hybrid dyes, trans-4-(4′-N,N-dialkylaminostyryl)-N-methyl pyridinium [Cd(SCN)3−]n [alkyl = Me(1), Et(2), Pr(3) and n–Bu(4)] have been successfully synthesized from hybrids of inorganic polymers and organic chromophores. The structures of four new hybrid dyes were characterized by single-crystal X-ray diffraction first. The particular features of the hybrid dyes are (1) the inorganic anions form isolated polymeric one-dimensional zig-zag chains of [Cd(SCN)3−]n with an extended π-conjugation system within the polymeric –[M–S–C≡N]–M… chain and high polarizabilities; and (2) the organic cationic chromophores determine their optical properties. Experimental results revealed that the TPA cross-section values and overall energy conversion efficiencies of hybrid dyes with different alkyl pendant groups have obviously increased from 1 to 4, and in particular, have been substantially enhanced compared to their corresponding iodide analogues 1′–4′. Therefore, we speculate that such increases are attributable to arrangements of infinite anionic [Cd(SCN)3−]n chains and synergic effects with chromophore cations.

LASING PROPERTIES OF A NEW TWO-PHOTON-ABSORBING MATERIAL TRANS-4-[p- (N-HYDROXYETHYL-N-ETHYLAMINO)STYRYL]- N-METHYLPYRIDINIUM p-TOLUENE SULFONATE

A new dye trans-4-[p-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridinium p-toluene sulfonate (HEASPS) has been synthesized. The two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped (TPP) frequency up-converted lasing properties of this new dye were experimentally studied. This new dye has a TPA cross-section of σ2 = 4.7 × 10-48 cm4 · s/photon at 1064 nm, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 625 nm up-converted lasing energy is 3.6% at the pump energy level of 4 mJ.

Synthesis and Properties of a New Two-photon-absorbed Material Heasps

A new dye Trans-4-[p-(N-hydroxyethyl-N-ethyiamino)styryl]-N-methylpyridinium p-toluene sulfonate (HEASPS) was synthesized, and the two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped (TPP) frequency up-converted lasing properties of this new dye were experimentally studied. This new dye has a moderate TPA cross-section of\\sigma2 = 4.7 × 10−48 cm4 .s/photon at 1064nm, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 626 nm up-converted lasing energy is 18.2% at the pump energy level of 1.9 mJ.

Studies on the lasing properties of a new two-photon absorbing material HEASPI

A new dye, trans-4-[ p-( N-ethyl- N-hydroxyethylamino)styryl]- N-methylpyridinium iodide has been synthesized, and the two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped frequency up-converted lasing properties of this new dye were experimentally studied. This new dye has a TPA cross-section of σ 2=7.0×10 −48 cm 4 s/photon at 1064 nm, and exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 632 nm up-converted lasing energy is 4.3% at the pump power of 4 mJ.

Optical properties of a new two-photon absorbing chromophore

A new dye, trans-4-[p-(pyrrolidinyl)styryl]-N-methylpyridinium iodide, has been synthesized, and the two-photon-absorption (TPA), TPA-induced frequency upconversion emission, and two-photon-pumped (TPP) frequency upconverted lasing properties of this new dye were experimentally studied. This new dye has a moderate TPA cross section of varsigma(2) = 5.7 x 10(-48) (cm(4) s(-1))/photon at 1064 nm but exhibits high lasing efficiency. The slope efficiency of the TPP cavity laser with this new dye as the laser medium is 1.6%.

Studies on two-photon pumped frequency up-converted lasing properties of a new material HMASPS

Abstract A new dye trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium p-toluene sulphonate (abbreviated as HMASPS) was synthesized, the two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped (TPP) frequency up-converted lasing properties of HMASPS were experimentally studied. This new dye has a moderate TPA cross-section of σ2 = 6.0 × 10−48 cm4 s photon−1, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 630 nm up-converted lasing energy is 4% at a pump energy level of 4mJ.

Two-photon pumped frequency up-converted lasing properties of a new material DEASMPI

A new dye Trans-4-[p-(N,N-diethylamino) styryl]-N- methylpyridinium iodide (abbreviated as DEASMPI) has been synthesized. The two-photon absorption (TPA), TPA-induced frequency up- conversion emission, and two-photon pumped (TPP) frequency up- converted lasing properties of this new dye have also been experimentally studied. This new dye has a moderate TPA cross section of ?2 = 6.9x 10-48 cm4.s/photon at 1064-nm, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064-nm pump pulse energy to the 628-nm up-converted lasing energy is 3.2% at the pump energy level of 3 mJ.

Studies on two-photon pumped frequency up-converted lasing properties of a new material HMASPS

A new dye trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium p-toluene sulphonate (abbreviated as HMASPS) was synthesized, the two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped (TPP) frequency up-converted lasing properties of HMASPS were experimentally studied. This new dye has a moderate TPA cross-section of σ2 = 6.0 × 10−48 cm4 s photon−1, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 630 nm up-converted lasing energy is 4% at a pump energy level of 4mJ.

Heterocycle-based materials for frequency-upconverted lasing

We report on the synthesis and characterization of a novel series of heterocycle-based chromophores for third order non-linear optics (NLO), showing enhanced two-photon absorption activity and frequency-upconverted lasing efficiency. The parent compound is a push-pull system where a pyridinium ion acts as acceptor group and N-methylpyrrole as a donor. Its efficiency in the two-photon-pumped lasing conversion from 800 to 543 nm is one of the highest ever reported. We show here the role of the position and nature of substituents in the tuning and optimization of the lasing wavelength and conversion efficiency.

Push-Pull Organic Chromophores for Frequency-Upconverted Lasing

Properly designed organic molecules where a π-conjugated bridge is end-capped by an electron-donor and electron-withdrawing group (push–pull chromophores) can show, under specific conditions, frequency-upconverted lasing emission. Materials based on these dyes are therefore able to convert the emission of a cheap and easily available infrared (IR) laser (e.g., 800 nm radiation) into more useful visible (vis) laser emission via a two-photon absorption induced fluorescence phenomenon. The design of the molecular structure, the substituent effect, and modulation of the electronic and geometric parameters can be used in order to optimize and tune frequency emission and conversion efficiency. Examples of some of the best dyes reported to-date and organic design strategies employed are discussed in this article.