Optical Properties of a New Two-photon Absorption Dye DEASPI

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｔｗｏ ｐｈｏｔｏｎａｂｓｏｒｐｔｉｏｎ (ＴＰＡ)ｉｓａｐｒｏｃｅｓｓｉｎｗｈｉｃｈｔｗｏｐｈｏｔｏｎｓａｒｅｓｉｍｕｌｔａｎｅｏｕｓｌｙａｂｓｏｒｂｅｄｔｏａｎｅｘｃｉｔｅｄｓｔａｔｅｉｎａｍｅｄｉｕｍｖｉａａｖｉｒｔｕａｌｓｔａｔｅ .ＴＰＡｉｎｔｅｎｓｉｔｙｉｓｃｈａｒａｃｔｅｒｉｚｅｄｂｙＴＰＡｃｒｏｓｓｓｅｃｔｉｏｎ .ＳｕｃｈｍａｔｅｒｉａｌｓｗｉｔｈｌａｒｇｅＴＰＡｃｒｏｓｓｓｅｃｔｉｏｎｈａｖｅｒｅｃｅｉｖｅｄｃｏｎｓｉｄｅｒａｂｌｅａｔｔｅｎｔｉｏｎｉ…     

Temporal and spectral properties of picosecond two-photon pumped cavity lasing of an organic dye HEASPS

The operation of cavity lasing of a two-photon absorption (TPA) organic dye, trans-4-[p-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridinium p-toluene sulfonate (abbreviated as HEASPS), by using a picosecond infrared laser as the pump source, is reported. The lifetimes of TPA fluorescence of this dye in different solvents were measured. Temporal profiles of cavity lasing show obvious oscillations and magnification of the feedback light. By using the difference of re-absorption coefficients at different conditions, we explained the blue shift for cavity lasing and superradiance compared with TPA-induced fluorescence. The long lifetime of fluorescence is helpful to the generation of cavity lasing. Received: 18 June 2001 / Revised version: 5 November 2001 / Published online: 17 January 2002     

Two-photon absorption-induced optical properties of a new lasing dye in two solvents

Pumped by an infrared lasing and its frequency-doubling source, the fluorescence and superradiance emission properties of a new lasing dye trans-4-[4^′-(N,N-diethylamino)styryl]-N-methyl pyridinium methyl sulfate (abbreviated DEASPS), have been studied in benzyl alcohol and chloroform. The two-photon absorption (TPA) and emission properties of DEASPSare influenced by the solvents used. The emission wavelength of the dye in benzyl alcohol is redshifted relative to that in chloroform. The lifetime of two-photon absorption-induced fluorescence is about 529 ps in benzyl alcohol, whereas it is 340 ps in chloroform. Correspondingly, the one-photon-excited fluorescence lifetimes in the two solvents are also given. The upconversion efficiency of DEASPS in chloroform is higher than in benzyl alcohol. Finally, the effective molecular two-photon absorption cross-sections were measured by the nonlinear transmittance method. It is found that the optical limiting effect of the dye in benzyl alcohol is stronger than that in chloroform. Received: 3 May 2001 / Revised version: 6 July 2001 / Published online: 19 September 2001     

Linear and nonlinear optical properties of two-photon absorption dye doped linear copolymer

2-hydroxyethyl methacrylate (abbreviated as HEMA) and acrylonitrile have been used as the monomers to form a trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium p-toluene sulfonate (abbreviated as HMASPS) doped linear copolymer. The spectra of one and two-photon excited fluorescence and two-photon pumped superradiance and two-photon pumped lasing of the polymer all shifted to short wavelengths compared with the solution sample of the dye. The copolymer shows much longer one- and two-photon excited fluorescence lifetimes of nanoseconds. When pumped by the picosecond Nd:YAG laser, the superradiance and lasing can be simultaneously obtained. The maximum two-photon pumped lasing conversion efficiency is 3.3%. The place of the maximum upconversion efficiency of the copolymer does not coincide with that of the maximum nonlinear absorption.     

Properties of two-photon absorption-induced cavity lasing of an organic dye HEASPI pumped by picosecond infrared laser beam

The first operation of cavity lasing of a two-photon absorption (TPA) organic dye, trans-4-[p-(N-ethyl-N-hydroxyethylamino) styryl]-N-methylpyridinium iodide (HEASPI), by using picosecond infrared laser as pump source is reported in this paper. Temporal profile of cavity lasing shows obvious oscillations, and magnification of the feedback light can be obtained. By using the difference of re-absorption coefficient at different conditions, we explained the blue shift for cavity lasing and superradiance compared with TPA-induced fluorescence. The lifetime of TPA-induced fluorescence is measured to be 134 ps.     

Two-photon induced optical-power limiting and upconverted superradiance properties of a new organic dye HEASPI

A new organic dye trans-4-[p-(N-ethyl-N-hydroxyethylamino)styryl]-N-methylpyridinium iodide (abbreviated as HEASPI hereafter) with large two-photon absorption (TPA) cross section and excellent upconverted superradiance properties was synthesized in our group recently. The TPA cross section was measured to be σ₂′=7.0×10⁻⁴⁸ cm⁴ s/photon by using an open aperture Z-scan system. Linear absorption, single-photon induced fluorescence, two-photon induced fluorescence and two-photon pumped (TPP) upconverted superradiance properties were systematically studied. The highest net upconversion efficiency from the absorbed pump energy to the output upconverted superradiance energy is as high as 19.6% at the pump energy of 2.07 mJ from a mode-locked Nd : YAG picosecond laser. The dye solution also shows a clear optical power limiting effect.     

Measurement of two-photon excitation cross-section of a new symmetric-type fluorene derivative

A new dye, 2,7-bis(4-methoxystyryl)-9,9-bis(2-ethylhexyl)-9H-fluorene, has been synthesized, which is a d-π-d symmetrical-type fluorene derivative. The two-photon absorption (TPA) of this new dye has been experimentally studied by comparable two-photon-induced fluorescence method. This new dye has a TPA cross-section of at 790 nm/13 fs.     

Two-photon excitation properties of a class of novel organic dye chloride

We present the two-photon excited (TPE) upconverted fluorescence and lasing efficiencies of a class of new pyridinium chloride having donor-π-acceptor (D-π-A) structure. Based on the excitation upon 40 ps laser pulses at 1064 nm, the experimental results showed that: the red-shift of TPE fluorescence emission peaks and the TPE fluorescence lifetime were gradually increased with the enhancement of electron-donating capability of the donor. To a certain extent, the enhanced donor would increase the two-photon pumped (TPP) upconversion lasing efficiencies, but the overlong alkyl chains would result in decreased lasing efficiencies. We could obtain TPE fluorescence lifetime of 754 ps, TPP upconversion lasing efficiency of ∼8.4%, and TPA cross-section of 6.14 × 10⁻⁴⁹cm⁴s/photon in these compounds.     

Nonlinear optical characteristics and lasing ability of merocyanine dyes having different solvatochromic behaviour

Lasing characteristics and two-photon absorption (TPA) of merocyanine dyes with solvatochromism of different types are first investigated. Efficient lasing is excited in solutions pumped by radiation of the 2nd harmonic of a Nd-YAG laser (532 nm) with the lasing efficiency exceeding 40% and by XeCl laser radiation (308 nm) with the lasing efficiency up to 19%. The TPA cross-section at a wavelength of 1064 nm is determined. It is established that for merocyanines possessing the highest positive and negative values of solvatochromism, the TPA cross-section reaches maximum values of 115 and 125 GM, respectively. Influence of the special features of the electronic structure, spectral and luminescent properties, solvatochromic behavior, and nature of the medium on the lasing characteristics and nonlinear absorption of merocyanine dyes is investigated. Prospects for merocyanine application in modern optical technologies are demonstrated.     

Two-photon absorption and nonlinear optical properties of a new organic dye PSPI

Trans-4-[p-(pyrrolidinyl)styryl]-N-methylpyridinium iodide (abbreviated as PSPI thereafter) is a two-photon absorption (TPA) dye newly synthesized by our research group. It possesses much larger TPA cross-section and much stronger upconversion fluorescence emission than those of common organic dye (such as rhodamine) when excited with near infrared (IR) radiation. TPA spectrum and upconversion efficiency spectrum of HEASPI solution at various wavelengths were measured. There is 34 nm blue shift for the central wavelength of the TPA induced absorption peak compared with two times of the linear absorption peak. The biggest molecular TPA cross-section σ₂^′ is 2.85×10⁻⁴⁷ cm⁴ s/photon at 930 nm. At 1064 nm, σ₂^′ is 3.12×10⁻⁴⁸ cm⁴ s/photon. The highest efficiency is 3.9% at 1010 nm, whereas 2.9% at 1064 nm. Its optical power limiting properties at 930 nm have also been illustrated.     

有机染料HEASPS在不同波长时的激发态吸收和双光子吸收性质研究

提出了有机染料反式 4 [4′ (N 羟乙基 N 乙基胺基 )苯乙烯基 ] N 甲基吡啶对甲苯磺酸盐 (简称HEASPS)非线性吸收的三态模型。认为在较短波长 (<1 0 0 0nm)时 ,双光子吸收和激发态吸收同时存在。成功地解释了该染料双光子吸收峰相对线性吸收峰的两倍的明显蓝移 ,以及最高上转换效率波长相对最强吸收波长的明显红移。提出了一种新的计算方法 ,利用不同波长的非线性透过率和不同波长的上转换效率 ,求出了该染料的双光子吸收截面和激发态吸收系数。     

Properties of two-photon fluorescence and superradiance of a new organic dye C46H51N2B

Linear and nonlinear optical properties of a new organic dye, trans-4-[p-(N-n-butyl-N-n-butylamino)-styryl]-N-methyl-pyridinium tetraphenylborate solution in dimethyl formamide (DMF) have been studied systematically. When excited with mode-locked picosecond 1 064 nm laser beam, intense upconversion fluorescence and superradiance can be obtained. The temporal behaviors of one-photon absorption and two-photon absorption (TPA) fluorescence and superradiance have been studied. The highest upconversion efficiency was found to be 4.1% at a pump energy of 4 mJ. By using an optical parameter amplifier (OPA) as the pump laser, the nonlinear transmittance and upconversion efficiencies of the dye solution at different wavelengths were measured. The strongest linear absorption was found at a wavelength of 930 nm whereas the highest upconversion efficiency was at 1 030 nm. The 100 nm red-shift for the highest upconversion efficiency wavelength compared with the strongest nonlinear absorption are caused by excited state absorption. Received 17 October 2001 and Received in final form 21 December 2001     

Nonlinear optical properties of a new two-photon-absorption organic dye: HEASPS

Trans-4-[p-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridinium p-toluene sulfonate (abbreviated as HEASPS) is a two-photon-absorption (TPA) dye newly synthesized by our research group. It possesses a much larger TPA cross-section and much stronger upconversion fluorescence emission than those of common organic dyes (such as rhodamine) when excited with near-infrared (IR) radiation. TPA spectrum and upconversion efficiency spectrum of HEASPS solution at different wavelengths have been measured. The largest molecular TPA cross-section σ₂ ^′ is measured to be 2.06×10^-47 cm⁴ s/photon at 930 nm. At 1064 nm, σ₂ ^′ is 2.71×10^-48 cm⁴ s/photon, which is only one-ninth of that at 930 nm. The upconverted lasing efficiency spectrum has been measured at different wavelengths. The highest efficiency is 5.1% at 1020 nm, whereas it is 3.5% at 1064 nm. Its optical-power-limiting properties at 930 nm have also been illustrated. Received: 30 November 2000 / Published online: 27 April 2001     

Two-photon-pumped amplified spontaneous emission and cavity lasing of an organic dye HEASPS in PHEMA polymer

Two-photon-absorption (TPA)-induced upconverted amplified spontaneous emission (ASE) and cavity lasing of a styrylpyridinium dye: trans-4-[p-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridinium p-toluene sulfonate (abbreviated as HEASPS) in poly(2-hydroxyethyl methacrylate) (abbreviated as PHEMA) polymer were observed under a picosecond pump condition. The spectral and temporal behaviors of TPA-induced fluorescence, ASE and cavity lasing were studied. The cavity lasing with a total oscillation time of more than 200 ps was achieved when pumped with 1064-nm, 50-ps laser irradiation. The population inversion could persist for three times longer than the duration of the pump pulse. The gain coefficients of the dye-doped polymer at various wavelengths were calculated based on cavity lasing spectra and one-photon fluorescence spectra. PACS 78.20.Ek; 42.65.Ky; 42.65.Re; 78.47.+p     

Simulating resonance-mediated two-photon absorption enhancement in rare-earth ions by a rectangle phase modulation

Improving the up-conversion luminescence efficiency of rare-earth ions via the multi-photon absorption process is crucial in several related application areas. In this work, we theoretically propose a feasible scheme to enhance the resonance-mediated two-photon absorption in Er~(3+) ions by shaping the femtosecond laser field with a rectangle phase modulation. Our theoretical results show that the resonance-mediated two-photon absorption can be decomposed into the on-resonant and near-resonant parts, and the on-resonant part mainly comes from the contribution of laser central frequency components, while the near-resonant part mainly results from the excitation of low and high laser frequency components.So, the rectangle phase modulation can induce a constructive interference between the two parts by properly designing the modulation depth and width, and finally realizes the resonance-mediated two-photon absorption enhancement. Moreover, our results also show that the enhancement efficiency of resonance-mediated two-photon absorption depends on the laser pulse width(or laser spectral bandwidth), final state transition frequency, and intermediate and final state absorption bandwidths. The enhancement efficiency modulation can be attributed to the relative weight manipulation of on-resonant and near-resonant two-photon absorption in the whole excitation process. This study presents a clear physical insight for the quantum control of resonance-mediated two-photon absorption in the rare-earth ions, and there will be an important significance for improving the up-conversion luminescence efficiency of rare-earthions.     

两个新合成化合物EPVPC和OPVPC非线性光学特性的理论研究

在杂化密度泛函理论（DFT/B3LYP）的水平上，研究了最新实验室合成的两个化合物分子9-乙烷基-3-{2-[4-2-吡啶-4-乙烯基苯]-乙烯基}-9氢咔唑（EPVPC）和9-十八烷基-3-{2-[4-2-吡啶-4-乙烯基苯]-乙烯基}-9氢咔唑（OPVPC）的非线性光学特性。理论结果与现有的实验测量结果符合得的较好。利用扩展的少态模型方法计算了分子的双光子吸收截面，结果表明三态模型可以很好地描述它们的最大双光子吸收截面。数值模拟显示这两个化合物都具有较大的双光子吸收截面，并且，在低频范围内，OPVPC分子比EPVPC分子显示出较强的双光子吸收特性。     

Up-conversion luminescence tuning in Er~(3+) -doped ceramic glass by femtosecond laser pulse at different laser powers

The up-conversion luminescence tuning of rare-earth ions is an important research topic for understanding luminescence mechanisms and promoting related applications. In this paper, we experimentally study the up-conversion luminescence tuning of Er~(3+)-doped ceramic glass excited by the unshaped, V-shaped and cosine-shaped femtosecond laser field with different laser powers. The results show that green and red up-conversion luminescence can be effectively tuned by varying the power or spectral phase of the femtosecond laser field. We further analyze the up-conversion luminescence tuning mechanism by considering different excitation processes, including single-photon absorption(SPA), two-photon absorption(TPA), excited state absorption(ESA), and energy transfer up-conversion(ETU). The relative weight of TPA in the whole excitation process can increase with the increase of the laser power, thereby enhancing the intensity ratio between green and red luminescence(I_(547)/I_(656)). However, the second ETU(ETU2) process can generate red luminescence and reduce the green and red luminescence intensity ratio I_(547)/I_(656), while the third ESA(ESA3) process can produce green luminescence and enhance its control efficiency. Moreover, the up-conversion luminescence tuning mechanism is further validated by observing the up-conversion luminescence intensity, depending on the laser power and the down-conversion luminescence spectrum under the excitation of 400-nm femtosecond laser pulse. These studies can present a clear physical picture that enables us to understand the up-conversion luminescence tuning mechanism in rare-earth ions, and can also provide an opportunity to tune up-conversion luminescence to promote its related applications.     

Nonlinear two-photon absorption properties induced by femtosecond laser with the films of two novel anthracene derivatives

Two novel anthracene derivatives containing 4-vinylpyridine (FPEA) and 2-vinylpyridine (TPEA) poly(methyl methacrylate) films are prepared on quartz glass substrates. Their nonlinear absorption properties are investigated by using a 120-fs, 800-nm Ti:sapphire femtosecond pulsed laser operating at a 1-kHz repetition rate. The unique nonlinear absorption properties of these new compounds are observed by utilizing a Z-scan system. These two-photon absorption (TPA) properties are proven by the two-photon fluorescence excited at 800 nm. The FPEA and TPEA films have nonlinear TPA coefficients of 0.164 and 0.148 cm/GW and the TPA cross sections of 3.345 × 10-48 and 3.081 × 10-48 cm4 ·s/photon, respectively. The influence of the chemical structures on the nonlinear TPA properties of the compounds is also discussed. The highly nonlinear TPA activities of the films implied that the new anthracene derivatives are suitable materials with promising applications in super-high-density three-dimensional data storage and nano- or microstructure fabrication.     

Ultrafast measurement of two-photon absorption by loss modulation

We demonstrate a direct and sensitive technique for measuring two-photon absorption (TPA). An intensity-modulated femtosecond laser beam passes through a sample exhibiting TPA. A TPA signal at twice the modulation frequency is then generated and subsequently measured by a lock-in amplifier. The absolute TPA cross section of Rhodamine 6G at 800nm is found to be (15.3+/-2.0)x10(-50) cm(4) s/photon and agrees well with previously published results obtained with much higher intensity [J.Chem.Phys.112, 9201 (2000)]. Our method may be especially useful in measuring nonlinear absorptions of nonfluorescent materials.     

Two-photon pumping of random lasers by picosecond and nanosecond lasers

We experimentally demonstrated two-photon pumping of random lasers using picosecond and nanosecond pump lasers. The picosecond laser pumping experiment was performed with 400 ps laser pulses at 770 nm, and the gain media was a Coumarin 480D dye solution doped with TiO₂ nanoparticles. Onset of laser action was observed at a pump laser pulse energy below 500 μJ. The nanosecond laser pumping experiment was performed with 7 ns laser pulses at 1064 nm, and the gain media was a Rhodamine 640 dye solution doped with TiO₂ nanoparticles. Onset of laser action was observed at a pump laser energy ∼18 mJ. Our results suggest that there exists an optimal pulse duration of the pumping laser in two-photon pumped random lasing that leads to minimum photodamage of the gain media and still keeps a high pumping efficiency. PACS 33.50.Dq; 42.55.Mv; 42.55.Zz