Study of organic dye lasers nanogold - Doped active medium for generation of short pulses by distributed feedback lasers

MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY ...*** NGUYEN THI MY AN STUDY OF ORGANIC DYE LASERS NANOGOLD-DOPED ACTIVE MEDIUM FOR GENERATION OF SHORT PULSES BY DISTRIBUTED FEEDBACK LASERS Major: Optics Code: 9440110 SUMMARY OF PHYSICS DOCTORAL THESIS Ha Noi – 2019 The work was completed at the Center for Quantum Electronics, Institute of Physics, Vietnam Academy of Science and Technology Supervisor: 1. Assoc. Prof. Dr. Do Quang Hoa 2. Dr. Nghiem Thi Ha Lien Referee 1: Referee 2: Referee 3: The thesis will be presented and defended at the Scientific Committee of Institute of Physics held in: ........................................................................................................... at........................................................................................................ The thesis can be found at the library: - National Library of Hanoi - Library of Institute of Physics, VAST 1 INTRODUCTION 1. Recent necessary of the topics Short pulse dye lasers recently become necessary instruments in many laboratories in Vietnam and in the world, also. However, the investigation for developing laser active medium is still attracted in many laboratories on optics and photonics. Moreover, the achievements in nanostructured materials have been bringing numerous applications in both the science and human life. Especially, gold nanoparticles (GNPs) with different sizes have become attractive subjects due to their distinguished properties. Thus, in this research, the study and preparation of new laser active medium to be used for the laser resonance cavity included the mixture of the dye and nanostructured metallic particles is focused. Research purpose: Preparation and characterization of GNPs-doped active medium based on dye molecules in PMMA applied to generate short pulses in the range of pico-seconds by using distributed feedback dye lases (DFDL) configuration are aimed. Research content: To fulfill the investigation purposes, the following work have been carried-out: - Researching technology of preparation of the active mediums for dye lasers with doped GNPs in solid states. - Characterization of optical properties of dye active mediums for doped GNPs. - Theoretical simulation of dynamic processes of emission of pulse DFDL, using the active doped mediums. - Testing performance of dye short-pulse lasers using dye active medium doped with GNPs. 2 CHAPTER 1. OVERVIEW OF THE DYE LASERS, LUMINESCENT ORGANIC DYES AND GOLD NANOPARTICLES 1.1. Dye lasers A dye laser is a typical laser which uses an organic dye as the lasing medium. Due to these laser dyes contained double bonds conjuncted to functional group, its could be strongly able to absorb in the wide spectral band from ultratviolet to visible. In this thesis, we used the dye DCM (4-(Dicyanomethylene)-2- methyl-6-(4-dimethylaminostyryl)-4H-pyran) for the study. It can be explained by special properties of DCM such as: the DCM molecule possesses both donor and acceptor behavior, leading to a large range of emission wavelengths (~ 100 nm) in visible light; DCM molecules strongly absorbs in shorter wavelengths than the peak of absorption resonance plasmon band of GNPs, therefore it is suitable for our research on the mixture medium of dyes and GNPs. Besides, the lasers having ability of the wavelength selectivity could be easy choose desired continuous wavelengths in the emission range of DCM. 1.2. Optical properties of nanostructured metallic materials, Gold nanoparticles As known, nanostructured materials possess most special properties. Due to a small size (much smaller than the wavelengths of ultra-violet and visible range), all the laws of classic optics used to explain the phenomena occured when light interacts with the materials are more unsatisfied. The resonance oscilation of the electron cloud on the surface of metallic nanoparticles (surface plasmon resonance - SPR) has been applied to the explaination of quantum confinement and quantum effect occured on the nanomaterials. 3 At the interface between nanostructure metals and vincinity medium, surface plasmonic effect exists in a smaller space than the typical optical materials. In other side, metallic nanoparticles strongly influence on the optical properties of the medium, like receiver and emitter “anten”. For example, a nanoparticles of the precious metal with 10 nm diameter possesses a extinction coefficient of ca. 107 M- 1cm-1 or larger in two orders of magnitude in comparison with a typical value of the organic laser dye. 1.3. Short pulse dye laser 1.3.1. Working principle of dye laser Dye laser performances on the gain medium having two large energy levels up-down, that can emit a large band. 1.3.2. Several types of configurations of dye lasers emiting pico- second pulses: In this section several configurations of dye lasers emiting pico- second pulses were presented. 1.3.3. Distributed feedback (DFB) dye laser Distributed feedback (DFB) dye laser is based on the Bragg reflect effect without mirrors in resonance cavity. The optic resonance occured when light beam propagates in a medium existed the modulation of gain and refractive index to be suitable to light wavelength, which leads to burn out the laser emission. Characteristics of DFDL lasers * Posibility to continuously tunable wavelengths * High monochromatic * Emission of single short pulses 4 Fig. 1.1: Schema of working principle of a DFDL laser. CHAPTER 2: PREPARATION OF ACTIVE MEDIUMS FOR DYE LASERS The difference of the mobility of the components in the active medium allows to investigate the characteristics and optical effects, as well as the interact between the components. Thus the medium for the dye laser in solutions (in ethanol) and in the solid state form (in PMMA) were prepared for study. 2.1. Initial materials and equipments used 2.1.1. Initial materials Organic dyes DCM, GNPs Au@PEG-COOH in spherical shape (d20 nm), Methyl methacrylate (MMA), Azobisisobutyronitrile (AIBN). 2.1.2. Equipments Ultrasonic stirrer ELMASONIC S30, Thermal oven with temperature T < 200oC), spincoating, etc. 2.1.3. Preparation of GNPs and attachment of HS-PEG-COOH. Sphere-shape GNPs were prepared by Turkevich method. 2.1.4. Changing active medium for Gold nanoparticles GNPs dispersed in water have been re-dispersed in MMA solvent for avoiding water, because water was not soluble MMA, moreover DCM molecules were easy decomposed in water. Laser lLLaser lL lp lp q q z L L Interference pattern Biến điệu gain )()( tT T n tn          Laser ra Laser ra Gain modulation Laser output Laser output 5 2.2. Active medium in solution for dye lasers 2.2.1. Preparation of DCM solutions Table 2.1: Concentration of DCM dye in ethanol. Sample DCM concentration (M) Sample 1 3.0×10-5 Sample 2 1.0×10-5 Sample 3 5.0×10-6 Sample 4 1.0x10-6 Table 2.2: Concentration of DCM dye in MMA solution Sample DCM concentration (M) Sample 1 2.5×10-6 Sample 2 2.0×10-6 Sample 3 1.5×10-6 Sample 4 2.0×10-7 Sample 5 5.0 10-7 2.2.2. Doped medium of DCM/GNPs dye Table 2.3: Concentration of DCM and GNPs in ethanol. Sample DCM concentration (mol/L) GNPs volume (particles/ml) Sample 1 1.0x10-4 M 5.0x109 Sample 2 1.0x10-4 M 1.0x1010 Sample 3 1.0x10-4 M 1.5x1010 Sample 4 1.0x10-4 M 2.0x1010 6 Table 2.4: Concentration of DCM and GNPs in MMA solution Sample DCM concentration (mol/L) GNPs volume (particles/ml) Sample 0 3.0x10-5 0 Sample 1 3.0x10-5 1.0x1010 Sample 2 3.0x10-5 1.5x1010 Sample 3 3.0x10-5 2.0x1010 Sample 4 3.0x10-5 3.3x1010 2.3. Preparation active medium for dye laser with doping GNPs in PMMA matrices (DCM/GNPs/PMMA) 2.3.1. Active medium with PMMA matrice Dye laser solid state active medium was prepared by polymerization of MMA monomers. 2.3.2. Template for preparation Solid state active medium was prepared in a cubic shape of 1x1x2,5 cm3 size (similar to cuvet). Synthesis process for polymers was carried-out at temperature of ~ 500C (Fig. 2.1). 2.3.3. Preparation of doped solid state active mediums Solid state active mediums were prepared by polymerization of MMA doped DCM dye. 2.2.3.1. Preparation of solid state active mediums DCM/PMMA a) Preparation of white samples Fig. 2.1. Template for preparation solid state active mediums. 7 The initial materials have been used: monomer MMA and catalytic AIBN. MMA solution for each experimental sample is 2000 µl. There are 5 samples with different weight of AIBN. Table 2.5: Materials and concentration. Sample AIBN (mg) MMA (µl) T1 1mg 2000 T2 2mg 2000 T3 3mg 2000 T4 4mg 2000 T5 5mg 2000 Solid state samples prepared with 3 mg of AIBN have a high homogeneity, best quality and without bubbles. They were used for all experiments in the thesis. b) Preparation of DCM/PMMA active medium The aim: Preparation of solid state samples for studying of the active mediums with different DCM concentration. Table 2.6: Initial materials and concentration of DCM/PMMA. Sample DCM/MMA (M) DCM/MMA (µl) AIBN (mg) D1 1x10-2 2000 3 D2 5x10-3 2000 3 D3 1x10-3 2000 3 D4 5x10-4 2000 3 D5 1x10-4 2000 3 D6 3x10-5 2000 3 D7 1x10-5 2000 3 8 2.2.3.2. Preparation of PMMA/DCM doped with GNPs The GNPs “Au@PEG-COOH” were dispersed in MMA such as introduced in the first step of the samples preparation. Table 2.7: DCM/GNPs/PMMA samples with DCM of 10-3 M. Sample DCM (mol/l) GNPs/MMA (µl) DCM/MMA (µl) AIBN (mg) DA1 10-3 0 2000 3 DA2 10-3 4 2000 3 DA3 10-3 8 2000 3 DA4 10-3 12 2000 3 DA5 10-3 20 2000 3 Table 2.8: DCM/GNPs/PMMA samples with DCM of 10-4 M. Sample DCM (mol/l) Au/MMA (µl) DCM/MMA (µl) AIBN (mg) DA6 10-4 0 2000 3 DA7 10-4 4 2000 3 DA8 10-4 8 2000 3 DA9 10-4 12 2000 3 DA10 10-4 20 2000 3 Fig. 2.1: Active DCM mediums dispersed in PMMA matrice used for lasers. 9 2.4. The determination of parameters of the samples and applied techniques In this section we listed the methods and equipments to detect different parameters of the samples for researching, such as the UV- Vis absorption, fluorescence spectra, fluorescence lifetime, autocorrelation etc. CHAPTER 3: INVESTIGATION OF ACTIVE MEDIUM OF GNPs-DOPED DYE MOLECULES In this chapter we presented recent results of the investigation on the quenching and enhancement effects of laser dye in the active medium of GNPs-doped DCM. 3.1. Optical properties of active mediums in dye laser with doping sphere-shape GNPs 3.1.1. Samples preparation The samples were prepared according to describing in Chapter 2. Nd:YAG laser was used for pumping DFDL, dye and GNPs-doped PMMA samples were prepared in a bulk with a size of 1×1×2.5 cm3. 3.1.2. Optical characteristics of DCM in solution and solid-state medium 3.1.2.1. Absorption spectra of DCM dye in ethanol and MMA Absorption spectra of DCM dye in ethanol and MMA without GNPs dopant are presented in Fig. 3.1a and Fig. 3.1b, respectively. These spectra have a similar shape, however the bandwidth of the absorption spectra of DCM in ethanol is narrower than that in MMA, and the spectral intensity fast decay in the long wavelength side. This can be explained due to the weak interaction between dye 10 molecules and the solvent, which did not expand or change the states of the upper and lower energy states of the DCM molecules. 3.1.2.2. Absorption spectra of the DCM dye in PMMA matrice In the solid state matrice of PMMA the mobility of the DCM molecules is smaller than in solution. Thus the absorption spectra are broaden in the long wavelength side (Fig. 3.3). 3.1.3. Fluorescent spectra of GNPs-doped DCM in ethanol (DCM/GNPs/ethanol) Fig. 3.3: Absorption spectra of DCM dye in PMMA. Fig. 3.1: Absorption spectra of DCM dye in ethanol (a) and in MMA (b) 400 500 600 700 0.0 0.7 1.4 1 1x10 -5 M 2 5x10 -6 M 3 3x10 -6 M 4 1x10 -6 M A b s o rp ti o n I n te n s it y ( a .u ) Wavelength (nm) 400 500 600 0.00 0.02 0.04 0.06 0.08 0.10 1 DCM 2.5 10 -6 M 2 DCM 2.0 10 -6 M 3 DCM 1.5 10 -6 M 4 DCM 2.0 10 -6 M 5 DCM 5.0 10 -7 M 1 2 3 4 5 N o rm a li z e d a b s o rp ti o n ( a .u .) Wavelength (nm) 11 The intensity of fluorescence attained a maximum value when the GNPs/DCM equal to 1/20 (solution of 1x1010 particles/ml of GNPs, d ≈ 16 nm; solution of DCM is 1x10-4 M). When the GNPs concentration increased (c.a. >1x1010 particles/ml), the fluorescence intensity slowly increases, and then started decreasing. (Fig. 3.6) This can be explained due to the fluorescence enhancement by near-field interaction between GNPs and DCM molecules. After reached a saturation value, the fluorescence quenching is occurred due to the Foster and SET energy transfer. 3.1.4. Optical properties of GNPs-doped DCM in PMMA matrice 3.1.4.1. Absorption spectra of DCM/GNPs/PMMA In this experiment, concentration of DCM was maintained at 1×10-4 M, and the concentration of GNPs was varied. The intensity of absorption spectra of the DCM slightly increased with the increase of GNPs Fig. 3.6: Fluorescent spectra of DCM/GNPs in ethanol. 450 500 550 600 650 700 0 50 100 150 200 250 300 350 400 450 (1) DCM 1x10 -4 M (2) DCM+5x10 9 hat/ml (3) DCM+1x10 10 hat/ml (4) DCM+1,5x10 10 hat/ml (5) DCM+2,0x10 10 hat/ml (1) (2) (3) (5) (4) F lu o re s c e n c e i n te n s it y (a .u .) Wavelength (nm) Fig. 3.7: Absorption spetra of the active medium DCM/GNPs/PMMA. 350 400 450 500 550 600 650 0.0 0.5 1.0 1 DCM+1.0x10 10 par/mLGNPs 2 DCM+1.5x10 10 par/mLGNPs 3 DCM+2.0x10 10 par/mLGNPs 1 2 3 Wavelength (nm) A b s o rp ti o n i n te n s it y ( a .u .) 12 concentration from 5 l/ml to 20 l/ml (or from 0.5x1010 particles/ml to 2x1010 particles/ml) (Fig. 3.7). At low concentrations of GNPs, a slightly increase of the fluorescence intensity was also observed. This can be explained due to the appearance of the near-field interaction. Several molecules of DCM were adhered on the GNPs surface, resulting in higher absorption cross-section of DCM increased. With higher concentration of GNPs, the absorption intensity of the samples decreased. 3.1.4.2. Fluorescence of the dye of DCM/GNPs/PMMA Fluorescence spectra of DCM/GNPs/PMMA (DCM concentration of 3x10-4 M) vs. GNPs concentration under an excitation wavelength of 472 nm is shown in Fig. 3.8. From this figure one can see that the fluorescence intensity of DCM increased up to a maximum value at the GNPs concentration of 1.5x1010 particles/ml (Curve “2”), then decreased with increasing GNPs concentration (Curves “3, 4”). Fig. 3.8: Fluorescence spectra of DCM/GNPs/PMMA. The excitation wavelength l = 472 nm (DCM concentration is of 3x10-4 M). 500 600 700 800 0 20 40 1 1x10 10 par/ml 2 1,5x10 10 par/ml 3 2x10 10 par/ml 4 2,5x10 10 par/ml 1 2 3 4 F lu o re s ce n ce in te n si ty ( a .u .) Wavelength (nm) 13 This can be explained due to less mobility of the DCM molecules in the solid state host, thus the larger GNPs concentration, the smaller average distance between GNPs and DCM, resulting in clearer SET effect. This behavior of GNPs can be applied for controlling the emission of the dye centers around the particles. GNPs exhibited as an anten, emiting or detecting electromagnetic radiation. With low GNPs concentrations, when pumping source excited to fluorescence is presented, GNPs play a role of emitting energy, leading to the energy transfer from GNPs to DCM molecules. At higher GNPs concentration, the quenching of fluorescence radiation from DCM molecules occurred. With excitation wavelength of 532 nm, only fluorescence quenching was observed (Fig. 3.9). This can be explained as follows. When the excitation wavelength is closed to maximum of plasmonic absorption of GNPs, the bleaching occurred for the DCM molecules located on the GNPs surface. This result obtained is different from that observed in case when DCM solutions doped GNPs. Fig. 3.9: Fluorescence spectra of DCM/GNPs/PMMA. The excitation wavelength l = 532 nm (DCM concentration is 3x10-5 M). 14 3.1.5. Fluorescence lifetime of molecules of DCM/GNPs/PMMA For the solution samples, DCM molecules are easy affected by the polarization of the medium matrice. Therefore, the Fluorescence life time of DCM strongly dependent on both the solvent and doping materials (Fig. 3.10). Whereas, fluorescence lifetime of DCM in PMMA with different GNPs concentration (namely from 0 to 33 l of GNP solution of 1x1011 particles/ml) is presented in Fig. 3.11. The fluorescence of DCM molecules exhibited similarly to self-emission, the transition from higher energy levels almost did not change. Thus, solid state materials containing DCM doped with GNPs can be used for the active medium for lasers as they exist in solutions. 3.2. Influence of the light-to-heat of GNPs on DCM molecules 3.2.1. Thermal conversion of plasmonic effect of GNPs Fig. 3.10: Fluorescence lifetime of DCM doped with different GNPs in solution. Fig. 3.11: PL lifetime of DCM/GNPs/PMMA. 15 Light-to-heat effect between GNPs particles and around environment was simulated by Mie theory. This simulation can be applied for explanation of the experimental results obtained when GNPs particles with a diameter of 16 nm doped in the active medium of solid state DCM dye laser. 3.2.2. Fluorescence decay of DCM/GNPs/PMMA Light-to-heat effect strongly affected to the working time of the active medium of DFDL. Fig. 3.13 shows the decay of integrated fluorescence intensity over time of the active medium based on DCM/GNPs/PMMA pumped by secondary harmonic generation of the Nd:YAG laser. 3.2.3. The decay of dye laser intensity The stability of the DFDL is shown in Fig 3.15 at room temperature (RT) and 4 °C. At RT, the degradation curve of laser intensity is similarly to the fluorescence decay Fig. 3.13: Lowering process of photoluminescence vs time of the acive medium DCM/GNPs/PMMA at RT with cooling. 0 1000 2000 0 2000 4000 6000 1 1x10 -3 mol/l DCM 2 DCM/2x10 10 GNPs (T P ) 3 DCM/2x10 10 GNPs (T 4C ) 1 2 3 Pulses (x102) F lu o re s c e n c e n c e (a .u .) Fig. 3.15: The decay of laser intensity (532 nm, 140J, 5,6 ns, 10Hz). 0 500 1000 1500 2000 2500 0 3000 6000 9000 at 10 o C room temp. Pulses (x102) L a s e r in te n s it y ( a .u ) 16 curve. At temperature of (4 ± 1) °C, the unchanged laser intensity was maintained for a long time. CHAPTER 4. DISTRIBUTED FEEDBACK DYE LASER (DFDL) USING GNPs-DOPED SOLID STATE MEDIUM - Modeling theoretical simulation for solid-state DFDL laser used DCM/GNPs/PMMA. Calcultion of spectro-temporal evolution of the DFDL by Matlab language. - Studing the influence of the laser parameters on the laser properties for optimization of the performance of DFDL. - Experimentally researching the influence of some parameters of solid-state DFDL on laser properties. - Setup a DFDL equipment that can be applied in practice based on the results of both the theoretical and experimental research. 4.1. Theoretical research o