Dye IR144 Research Articles

Directional coupling with parity-time symmetric Bragg gratings.

Parity-time symmetric Bragg gratings produce unidirectional reflection around the exceptional point. We propose and explore directional coupling of gain and loss modulated waveguide Bragg gratings operating at around 880 nm with long-range surface plasmon polaritons. Step-in-width modulation of a Ag stripe supporting long-range plasmons combined with a periodic modulation of the cladding were used to balance the real and imaginary index perturbation of the gratings. IR140 dye molecules in solvent forms a portion of the uppercladding, providing gain under optical pumping. We investigate directional coupling between a pair of parity-time symmetric waveguide Bragg gratings operating near their exceptional point, arranged in various configurations - duplicate, duplicate-shifted and duplicate-flipped. We also investigate coupling to a bus waveguide and to a conventional waveguide Bragg grating. Unidirectional multi-wavelength reflection and coupled supermode conversion are predicted.

Magnetic on–off switching of a plasmonic laser

The nanoscale mode volumes of surface plasmon polaritons have enabled plasmonic lasers and condensates with ultrafast operation. Most plasmonic lasers are based on noble metals, rendering the optical mode structure inert to external fields. Here, we demonstrate active magnetic-field control over lasing in a periodic array of Co/Pt multilayer nanodots immersed in an IR-140 dye solution. We exploit the magnetic nature of the nanoparticles combined with mode tailoring to control the lasing action. Under circularly polarized excitation, angle-resolved photoluminescence measurements reveal a transition between lasing action and non-lasing emission as the nanodot magnetization is reversed. Our results introduce magnetization as a means of externally controlling plasmonic nanolasers, complementary to the modulation by excitation, gain medium, or substrate. Further, the results show how effects of magnetization on light that are inherently weak can be observed in the lasing regime, inspiring studies of topological photonics.

Plasmonic crystal with independently tunable double resonances

This paper reports the design and fabrication of large-area periodic arrays of metal nanostructures that can support dual-wavelength resonance with spatially overlapping hot spots. Gold films with protruding posts arranged in a rectangular lattice are stripped from silicon templates containing shallow hole arrays, defined by laser interference lithography. The plasmonic resonances at the band edges for the two orthogonal linear polarizations can be tuned independently by changing the corresponding lattice spacing. WSe2 monolayers and IR-140 dye molecules demonstrate directional and linearly polarized photoluminescence when coupled with such plasmonic crystals. The anisotropic lattice can enable enhancements at both the excitation and emission wavelengths. The emission is preferentially coupled to the first diffraction orders of the plasmonic crystals, resulting in a directional beam.

Drop-in two-dimensional electronic spectroscopy based on dual modulation in the pump-probe geometry

We report a compact design of two-dimensional electronic spectrometer (2DES) which can be built from any femtosecond broadband transient absorption setup using only a few optical elements and dual beam modulation by a single chopper blade. The dual pulse modulation design provides automatic extraction of the third order response as well as effective scatter suppression. Self-phasing of the 2D absorptive spectra is enabled directly by the pump-probe geometry. This passively stabilized instrument achieves interferometric phase stability of λ/300 at 800 nm. The laser dye IR140 was used as a model chromophore to demonstrate the function of the instrument. Two ground state conformers of IR140 are observed in the 2D spectra. The presented simple modification of standard transient absorption spectrometer grants a wider access to a next generation research tool with advantages of low cost, simple operation, and data extraction. Our report presents an alternative solution of bringing the ultrafast research in chemistry, biology, and physics to the forefront of modern science.

Design, fabrication and testing of gain SPR sensor chip

The gain Surface plasmon resonance (SPR) chip can compensate for the SPR loss, which can improve the sensitivity of the SPR analysis system. In this paper, we design an SPR chip that includes a glass substrate, a gain layer, and a metal layer. Wherein the gain layer is a film obtained by adding IR-140 fuel to different concentrations of methylene chloride in which polymethyl methacrylate (PMMA) is dissolved. Then, we prepared a series of chips with a specific gravity of 0.4%, 0.8%, 1.2%, and 1.6% for the IR-140 in the gain dielectric layer. The fitting effect of the 2nd to 11th order polynomial fitting on the SPR curve is studied, and the SPR curve in this paper is processed by the preferred ninth order polynomial fitting. Finally, by studying the relationship between the thickness of the gain layer and the absorption peak generated by the SPR chip, a chip having an IR-140 dye specific gravity of 0.4% is preferred. The gain layer of the gain SPR chip is also expected to be further studied to further increase its sensitivity.

Gain optimization, bleaching, and e-beam structuring of IR-140 doped PMMA and integration with plasmonic waveguides

The optimal IR-140 weight ratio concentration producing maximum gain in amplified spontaneous emission measurements in the near-infrared (~880 nm) is determined. The structures investigated consist of PMMA polymer thin films, doped with IR-140 dye molecules in 4 different concentrations (0.7%, 0.8%, 0.9% and 1.0%), spin-coated on a silica layer grown on silicon wafers. The maximum material gain was obtained for the 0.9% weight ratio sample. The polarization dependence of the gain medium was also investigated, and the gain found to be similar in the TE and TM orientations. Bleaching of the gain medium, characterized by a decrease in the material gain due to pumping, was also explored and found to be rapid for thin films. However, bleaching is reduced as the pump energy density is reduced, creating a trade-off between gain and film longevity. The bleaching disappears at a low pump repetition rate. The gain films were structured via e-beam lithography to demonstrate the feasibility of this method for integration of structured doped polymers within optical devices. Amplification of the long-range surface plasmon guided by a gold stripe covered by the gain medium is also demonstrated and the modal gain measured was measured (~65 cm−1) from which the material gain was deduced (~300 cm−1). The material should prove useful for demonstrating device ideas and concepts in plasmonics and nano-photonics.

Temporal resolution beyond the average pulse duration in shaped noisy-pulse transient absorption spectroscopy.

In time-resolved spectroscopy, it is a widespread belief that the temporal resolution is determined by the laser pulse duration. Recently, it was observed and shown that partially coherent laser pulses as they are provided by free-electron-laser (FEL) sources offer an alternative route to reach a temporal resolution below the average pulse duration. Here, we demonstrate the generation of partially coherent light in the laboratory like we observe it at FELs. We present the successful implementation of such statistically fluctuating pulses by using the pulse-shaping technique. These pulses exhibit an average pulse duration about 10 times larger than their bandwidth limit. The shaped pulses are then applied to transient-absorption measurements in the dye IR144. Despite the noisy characteristics of the laser pulses, features in the measured absorption spectra occurring on time scales much faster than the average pulse duration are resolved, thus proving the universality of the described noisy-pulse concept.

Moderately strong pump-induced ultrafast dynamics in solution

The transient transmittance spectra of laser dye IR144 in methanol were investigated experimentally in the moderately strong pump-probe field. Observed emission spectra in the red edge of the incident-field bandwidth, created by resonant impulsive stimulated Raman scattering (RISRS), display significant nonlinear intensity dependence as the pulse intensity increases. Dynamic perspectives of RISRS spectra can be understood well in a wavepacket picture. The excitation of high vibrational levels in the ground electronic state leading to the redshift of emissions presents high dependence of the pump-pulse intensity and ultrafast dynamical features, mapping the spatial overlap and separation of ground and excited wave functions and resolving the ultrafast vibrational relaxation in the femtosecond regime.

Single-mode lasers and parity-time symmetry broken gratings based on active dielectric-loaded long-range surface plasmon polariton waveguides.

Single-mode distributed feedback laser structures and parity-time symmetry broken grating structures based on dielectric-loaded long-range surface plasmon polariton waveguides are proposed. The structures comprise a thin Ag stripe on an active polymer bottom cladding with an active polymer ridge. The active polymer assumed is PMMA doped with IR140 dye providing optical gain at near infrared wavelengths. Cutoff top ridge dimensions (thickness and width) are calculated using a finite element method and selected to guarantee single-mode operation of the laser. Several parameters such as the threshold number of periods and the lasing wavelength are determined using the transfer matrix method. A related structure based on two pairs of waveguides of two widths, which have the same imaginary part but different real part of effective index, arranged within one grating period, is proposed as an active grating operating at the threshold for parity-time symmetry breaking (i.e., operating at an exceptional point). Such "exceptional point" gratings produce ideal reflectance asymmetry as demonstrated via transfer matrix computations.

Spatially nonreciprocal Bragg gratings based on surface plasmons

Using the concept of parity-time symmetry in optics, we propose a spatially non-reciprocal Bragg grating at near infrared wavelengths, operating with long-range surface plasmon polaritons, by employing balanced modulation of index and gain/loss in a step-in-width configuration. The index perturbation is created by stepping the width of an Ag stripe supporting long-range plasmons. Gain/loss modulation is generated by periodically doping the top polymer cladding of the structure with IR-140 dye molecules and pumping the grating optically from top. Loss exists inherently in the undoped regions due to plasmonic propagation loss. The transmission matrix method was employed as an accurate modeling technique to compute the reflectance and transmittance spectra of the proposed structures. Simulation results exhibit a strong reflectance from one end of the grating at about 880 nm as opposed to nearly no reflectance from the other end at the same wavelength.

A broadband ultrafast transient absorption spectrometer covering the range from near-infrared (NIR) down to green.

We present a new development for pump-probe absorption spectroscopy that allows the simultaneous measurement from the green part of the visible spectrum (510 nm) over the whole near-infrared range to >1600 nm, corresponding to 0.77-2.40 eV. The system is based on a sub-picosecond supercontinuum generated in bulk material used as a broadband probe that is dispersed with a custom-made prism spectrometer and detected by an InGaAs array with extended sensitivity to the visible. Two versions, with and without probe referencing, are implemented for operation at laser repetition rates of a few hertz and kilohertz, respectively. After presentation of the optical configuration of the spectrometer, its performance is characterized and further illustrated on two time scales, with the ultrafast radiolysis of isopropanol induced by a picosecond electron pulse and with the instantaneous response of a BK7 plate to a femtosecond light pulse. The photophysics of the dye IR-140 is resolved from the femto- to picosecond regime. Stable and easy day-to-day routine use of the spectrometer also can be achieved in non-optical laboratory surroundings. For operation in a hazardous environment, the optical probe beams can be transported to the detector unit by optical fibers.

Independent phasing of rephasing and non-rephasing 2D electronic spectra

Assigning absolute phase to two-dimensional (2D) third-order nonlinear optical signals generally requires acquiring both the rephasing and the non-rephasing signals and comparing the sum of the two to spectrally resolved pump-probe spectra. To date, however, Gradient Assisted Photon Echo Spectroscopy (GRAPES) has only been able to acquire rephasing spectra. Such a constraint requires a new phasing protocol. Here, we analytically prove that the rephasing and non-rephasing spectra can be phased independently using pump-probe signal. We verify this result holds even for finite duration pulses by simulation. This relationship holds for all 2D spectroscopies, not only GRAPES. In addition, we present improvements to GRAPES that enable acquisition of rephasing and non-rephasing signals in different phase-matched directions. We employ our phasing protocol to phase the data for laser dye IR-144, leading to reconstruction of purely absorptive 2D spectrum.

Sensitized near-infrared luminescence from erbium ion-associated complex with IR140 dye

In this study, the near-infrared luminescence emission of erbium ions is enhanced by 6-folds in intensity with an ion-associated erbium complex consisting of an IR140 dye cation. The energy-transfer process from the IR140 dye cation to the erbium ion has been modeled. Near-infrared luminescence of the erbium ion is sensitized intra-molecularly by the IR140 dye cation effectively, although the residual IR140 dye emission is still observed, indicating an incomplete energy transfer between the IR140 dye cation and the erbium ion. The main path of energy-transfer process is through the T1 → 4I11/2 transition with the operative mechanism to be Förster type.

Erratum: Aggregation Behaviors of Tricarbocyanine dye in Water and in AOT Reverse Micelles

The photophysical property of the tricarbocyanine dye IR144 has been extensively studied in non-aqueous solvents. However, as a potential near-infrared biomedical imaging probe, the photophysical property of IR144 in water is still little known. So, the aggregation behaviors of IR144 in water with steady-state absorption spectroscopy and integrated polarization dependent femtosecond pump-probe spectroscopy were investigated. Through comparing the absorption spectral bandshape of IR144 in water and in water pool of AOT reverse micelles, It is found that IR144 form dimer aggregates in water even at very low concentration (<1.0×10−7 mol·L−1). And the absorption spectrum of the IR144 aggregates always displays a bimodal feature, which is independent of the dye concentration ranging from 1.0×10−7 to 1.0×10−4 mol·L−1. For better understanding the aggregation behaviors of IR144 in water, we measured the ground state recovery kinetics and the reorientation kinetics of IR144 in water and in water pool of AOT reverse micelles (W0=[H2O]/[AOT], W0=40). It is found that the fluorescence quantum yield of IR144 in water is lower than that in water pool of AOT reverse micelles, and the reorientation time of IR144 in water is slower than that in water pool of AOT reverse micelles. Those kinetic measurements also verify that IR144 exists as dimer aggregates in water.

Aggregation Behaviors of Tricarbocyanine Dye in Water and in AOT Reverse Micelles

AbstractThe photophysical property of the tricarbocyanine dye IR144 has been extensively studied in non‐aqueous solvents. However, as a potential near‐infrared biomedical imaging probe, the photophysical property of IR144 in water is still little known. So, the aggregation behaviors of IR144 in water with steady‐state absorption spectroscopy and integrated polarization dependent femtosecond pump‐probe spectroscopy were investigated. Through comparing the absorption spectral bandshape of IR144 in water and in water pool of AOT reverse micelles, It is found that IR144 form dimer aggregates in water even at very low concentration (&lt;1.0×10−7 mol·L−1). And the absorption spectrum of the IR144 aggregates always displays a bimodal feature, which is independent of the dye concentration ranging from 1.0×10−7 to 1.0×10−4 mol·L−1. For better understanding the aggregation behaviors of IR144 in water, we measured the ground state recovery kinetics and the reorientation kinetics of IR144 in water and in water pool of AOT reverse micelles (W0=[H2O]/[AOT], W0=40). It is found that the fluorescence quantum yield of IR144 in water is lower than that in water pool of AOT reverse micelles, and the reorientation time of IR144 in water is slower than that in water pool of AOT reverse micelles. Those kinetic measurements also verify that IR144 exists as dimer aggregates in water.

Molecular quantum control landscapes in von Neumann time-frequency phase space

Recently we introduced the von Neumann representation as a joint time-frequency description for femtosecond laser pulses and suggested its use as a basis for pulse shaping experiments. Here we use the von Neumann basis to represent multidimensional molecular control landscapes, providing insight into the molecular dynamics. We present three kinds of time-frequency phase space scanning procedures based on the von Neumann formalism: variation of intensity, time-frequency phase space position, and/or the relative phase of single subpulses. The shaped pulses produced are characterized via Fourier-transform spectral interferometry. Quantum control is demonstrated on the laser dye IR140 elucidating a time-frequency pump-dump mechanism.

Dissecting Hidden Couplings Using Fifth-Order Three-Dimensional Electronic Spectroscopy

We report the demonstration of single-quantum 3D electronic spectroscopy. Utilizing the recently introduced gradient assisted photon echo (GRAPE) methodology, the fifth-order nonlinear polarization of the solvatochromatic dye IR144 corresponding to evolution through three sequential single-quantum coherences is measured. GRAPE, which allows a 2D slice of data to be acquired in parallel, permits a practical implementation of 3D spectroscopy at optical frequencies in a matter of minutes instead of hours. By spreading frequencies into a third spectral dimension, we can resolve features in the spectra that are otherwise obscured. For IR144, a previously unresolved cross peak originating from high frequency vibronic modes is observed in the spectrum. Theoretical modeling based on the cumulant expansion truncated at second order reproduces the main features of the experimental results. This experimental approach will enable further high dimensional spectroscopic experiments.

ChemInform Abstract: Synthesis and Characterization of InAs/InP and InAs/CdSe Core/Shell Nanocrystals.

The effect of the outer surface of core/shell nanocrystals on the fluorescence quantum yield was observed for InAs/InP and InAs/CdSe core/shells (see picture). For InAs/CdSe we observed substantial enhancement of the fluorescence quantum yield compared to the InAs core, and up to two times larger than the laser dye IR-140. Such core/shell nanocrystals have potential use as biological fluorescent markers in the near IR spectral range.

Optical dephasing in saturable-absorbing organic dye IR140

Room-temperature degenerate four-wave mixing in the forward two-pulse geometry, has been performed on ajet of organic saturable-absorbing laser dye IR140 dissolved in dimethylsulfoxide and ethylene glycol. Numerical solutions to the optical Bloch equation were fitted to the experimental data in order to extract a value of T2 = 50 +/- 5 fs for the homogeneous dephasing time; this value is comparable to those measured for similar organic dyes using other techniques.

Amplified spontaneous emission in the near infrared from a dye-doped polymer thin film

Although optical gain and lasing has been observed in the solid state for numerous organic molecules emitting at visible wavelengths, this is not the case in the infrared. Here, we show line-narrowing due to amplified spontaneous emission in the near infrared (960 nm) from a solid state organic thin film, made by spin-coating, a blend of the laser dye IR-140 and the polymer poly(methylmethacrylate). Line-narrowing becomes evident for excitation densities above 4.8 mJ cm −2, and is tunable between 920 and 970 nm, with a maximum gain value of 6.6 cm. Preliminary results using other near infrared-emitting dyes suggest that this may be a general approach.