Summary of physics doctoral thesis: Study of organic dye lasers nanogold doped active medium for generation of short pulses by distributed feedback lasers

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.

MINISTRY OF EDUCATION VIETNAM ACADEMY OF AND TRAINING 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: Assoc Prof Dr Do Quang Hoa 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 INTRODUCTION 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 CHAPTER 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)-2methyl-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 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 M1 cm-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 picosecond pulses: In this section several configurations of dye lasers emiting picosecond 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 lp lp q q Laser Laseroutput Laser output Laser z Interference pattern Laser lL Gain Biếnmodulation điệu gain L Laser lL  n  n(t )   T (t )  T  L 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 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 3.0×10-5 Sample 1.0×10-5 Sample 5.0×10-6 Sample 1.0x10-6 Table 2.2: Concentration of DCM dye in MMA solution Sample DCM concentration (M) Sample 2.5×10-6 Sample 2.0×10-6 Sample 1.5×10-6 Sample 2.0×10-7 Sample 5.0 10-7 2.2.2 Doped medium of DCM/GNPs dye Table 2.3: Concentration of DCM and GNPs in ethanol DCM concentration GNPs volume (mol/L) (particles/ml) Sample 1.0x10-4 M 5.0x109 Sample 1.0x10-4 M 1.0x1010 Sample 1.0x10-4 M 1.5x1010 Sample 1.0x10-4 M 2.0x1010 Sample Table 2.4: Concentration of DCM and GNPs in MMA solution Sample DCM concentration GNPs volume (mol/L) (particles/ml) Sample 3.0x10-5 Sample 3.0x10-5 1.0x1010 Sample 3.0x10-5 1.5x1010 Sample 3.0x10-5 2.0x1010 Sample 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 Fig 2.1 Template for size (similar to cuvet) Synthesis process preparation solid state for polymers was carried-out at active mediums temperature of ~ 50 C (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 The initial materials have been used: monomer MMA and catalytic AIBN MMA solution for each experimental sample is 2000 µl There are 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 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 D2 -3 5x10 2000 D3 1x10-3 2000 D4 -4 2000 D5 -4 1x10 2000 D6 3x10-5 2000 D7 -5 2000 5x10 1x10 Fig 2.1: Active DCM mediums dispersed in PMMA matrice used for lasers 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 DCM GNPs/MMA DCM/MMA AIBN (mol/l) (µl) (µl) (mg) DA1 10-3 2000 DA2 10-3 2000 DA3 10-3 2000 DA4 10-3 12 2000 DA5 10-3 20 2000 Sample Table 2.8: DCM/GNPs/PMMA samples with DCM of 10-4 M Sample DCM Au/MMA DCM/MMA AIBN (mol/l) (µl) (µl) (mg) DA6 10 -4 2000 DA7 10-4 2000 DA8 10-4 2000 DA9 10-4 12 2000 -4 20 2000 DA10 10 The intensity of maximum value when the GNPs/DCM equal to 1/20 (solution of 1x1010 particles/ml of GNPs, d ≈ 16 nm; 450 Fluorescence intensity (a.u.) fluorescence attained a (3) (1) 350 300 -4 (1) (2) (3) (4) (5) (2) 400 DCM 1x10 M DCM+5x10 hat/ml 10 DCM+1x10 hat/ml 10 DCM+1,5x10 hat/ml 10 DCM+2,0x10 hat/ml (5) 250 (4) 200 150 100 50 solution of DCM is -4 M) When the GNPs concentration 1x10 increased (c.a >1x1010 particles/ml), 450 500 550 600 650 700 Wavelength (nm) Fig 3.6: Fluorescent spectra of DCM/GNPs in ethanol 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 concentration of DCM was maintained at 1×10-4 M, and the concentration of GNPs was varied The intensity spectra of of the of 0.5 350 400 450 500 550 600 650 Wavelength (nm) DCM GNPs 1.0 DCM+1.0x10 par/mLGNPs 10 DCM+1.5x10 par/mLGNPs 10 DCM+2.0x10 par/mLGNPs 0.0 absorption slightly increased with the increase Absorption intensity (a.u.) In this experiment, 10 3 Fig 3.7: Absorption spetra of the active medium DCM/GNPs/PMMA 11 concentration from 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 concentration of 3x10 -4 of DCM/GNPs/PMMA (DCM 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”) Fluorescence intensity (a.u.) 2 40 10 1x10 par/ml 10 1,5x10 par/ml 10 2x10 par/ml 10 2,5x10 par/ml 20 500 600 700 800 Wavelength (nm) Fig 3.8: Fluorescence spectra of DCM/GNPs/PMMA The excitation wavelength l = 472 nm (DCM concentration is of 3x10-4 M) 12 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) 13 3.1.5 Fluorescence lifetime of molecules of DCM/GNPs/PMMA For the solution samples, DCM molecules are easy affected by the polarization of medium matrice Therefore, the the Fluorescence life time of DCM strongly dependent on both the solvent and doping Fig 3.10: Fluorescence lifetime of DCM doped with different GNPs in solution materials (Fig 3.10) Whereas, fluorescence lifetime of DCM in PMMA with different GNPs concentration (namely from 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 Fig 3.11: PL lifetime of with GNPs can be used DCM/GNPs/PMMA 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 14 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 effect strongly affected to the working time of the active medium of DFDL Fig 3.13 shows the decay of integrated fluorescence Fluorescencence (a.u.) Light-to-heat intensity over time of the 6000 DCM/2x10 GNPs (T4C) 10 2000 0 1000 2000 Pulses (x102) Fig 3.13: Lowering process of DCM/GNPs/PMMA by 1x10 mol/l DCM 10 DCM/2x10 GNPs (TP) 4000 active medium based on pumped -3 secondary harmonic generation of the photoluminescence vs time of the acive medium DCM/GNPs/PMMA at RT with cooling Nd:YAG laser 3.2.3 The decay of dye laser intensity o Fig 3.15 at room temperature (RT) and °C At RT, intensity similarly fluorescence to 6000 3000 the degradation curve of laser Laser intensity (a.u) the DFDL is shown in at 10 C room temp 9000 The stability of 0 decay 1000 1500 2000 2500 Pulses (x102) is the 500 Fig 3.15: The decay of laser intensity (532 nm, 140J, 5,6 ns, 10Hz) 15 curve At temperature of (4 ± 1) °C, the unchanged laser intensity was maintained for a long time CHAPTER 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 on the solid-state DFDL dye laser 4.1.1 Rate equations of two dissimilar components It is suggested that the peformance of a dye laser can be described by two broad energy levels (corresponding to a laser with four energy levels, as shown in Fig 4.1) S1 GNP p e 00 GNP S0 Fig 4.1: Schematic draw of energy levels in a laser doped with GNPs 16 To describe the energy levels transition in a dye laser doped GNPs, the rate equations has been shown in Ref [126], it consists of four equations describing spectro-temporal evolution of the laser emission of DFDL with intrinsic quenching parameters: 𝑑𝑛𝐴𝑢 𝑑𝑡 𝑑𝐸𝑖 (𝑡) 𝑑𝑡 𝑑𝑛𝑎 𝑑𝑡 = (𝐼𝑝 𝜎𝑝𝐴𝑢 + 𝜎𝑎𝐴𝑢 𝑐𝐼𝑎𝑖 (𝑡))(𝑛0𝐴𝑢 − 𝑛𝐴𝑢 (𝑡)) − 𝑛𝐴𝑢 (𝑡) −𝑛𝐴𝑢 [∑𝑘𝑖=1 𝜎𝑎𝑖𝐴𝑢 𝐸𝑖 (𝑡)], 𝜏𝐴𝑢 𝜎𝑠𝐴𝑢 𝑐 𝐸 (𝑡) 𝑛𝑎𝑢 (𝑡)𝐸𝑖 (𝑡) − 𝜏𝑖 , 𝜂 = 4.1) (4.2) 𝐴𝑢 = 𝐼𝑝 (𝑡)𝜎𝑝𝑎 [𝑁𝑎 − 𝑛𝑎 (𝑡)] + 𝐾𝑠 𝜎𝑎𝐴𝑢𝑎 𝑛𝐴𝑢 𝑐𝐸𝑖 𝜂 − 𝜎𝑒𝑎 𝑐𝑛𝑎 (𝑡)𝐼𝑎 (𝑡) − 𝜂 𝑛𝑎 (𝑡) 𝜎 𝑐[𝑁 −𝑛 (𝑡)]𝐼 (𝑡) + 𝑎𝑎𝑙 𝑎 𝜂 𝑎 𝑎 , 𝜏𝑎 𝑑𝐼𝑎𝑖 (𝑡) 𝑑𝑡 = (𝜎𝑒𝑎𝑖 −𝜎𝑎𝑎𝑖 )𝑐 𝜂 (4.3) 𝑛𝑎 (𝑡)𝐼𝑎𝑖 (𝑡) − 𝐼𝑎𝑖 (𝑡) Ω𝑛 (𝑡) 𝐾 𝜎 𝑐𝐼 (𝑡) + 𝜏𝑎 − 𝐹 𝑎𝐴𝑢𝜂 𝑎𝑖 , 𝜏𝑐 (𝑡) 𝑎 (4.4) where n0Au, na are the densities of GNP and DCM molecula in 1cm , respectively; nAu(t), na(t) – the average densities of GNPs and DCM at above energy level in 1cm3, respectively; τc – life time of a photon in the active medium equivalent that is considered as follows: 𝜏𝑐 = 𝜂𝐿3 [𝑛𝑎𝑖 (𝑡)𝜎𝑒𝑎𝑖 𝑉]2 8𝑐 𝜋2 = 𝜂𝐿3 𝜋 ∆𝜂(𝑡)) [( 2𝑐 𝜋 𝜆𝑖 𝑛𝑡ℎ = 𝛾𝑖 (𝑡) ) ] +( (4.5) 𝜋 ( ) 𝜎𝑒𝑎𝑖 𝐿 𝑉 (4.6) Equation (4.1) describes the changing rate of GNPs at the excited state by energy pumping and laser emission energy of the DCM molecules The change of resonance surface plasmon energy of GNPs is shown in equation (4.2) The energy transfer from/to molecules of dye DCM is described by equation (4.3) with KF and Ks – coefficients of the energy transfer This value is positive when the energy transfer 17 from GNPs to the dye molecule and – negative when energy transfer on opposite direction The change rate of the photon density in the active medium is shown in equation (4.4) 4.1.2 The influence of pumping rate At a pumping rate that is appropriate to the threshold, the single pulses can be observed When the pumping rate increases corresponding r/rth increases from 1.5 to above the ngưỡng, the pulse width decreases and then the secondary pulse occured due to the relaxation of the population at the higher energy level (Fig 4.2) 2.00E+015 (a) 4.00E+015 (b) 1.00E+015 2.00E+015 0.00E+000 0.00E+000 A19 635 635 A18 A24 640 A23 640 645 A28 A29 645 4.00E-012 8.00E-012 A33 650 1.20E-011 4.00E-012 X Time Axis (s) 8.00E-012 XTime Axis (s) 1.5 times above threshold Appr Threshold 6.00E+015 DCM = 1x10-3 M GPs = 1x1010par/ml 4.00E+015 (c) 2.00E+015 0.00E+000 A17 635 640 A22 A27 645 A32 650 4.00E-012 8.00E-012 Time (s) times above threshold Fig 4.2: Procedure of the DFDL spectrum according to the change of pumping rate 4.1.3 Influemce of GNPs concentration With increase of the GNPs concentration, the energy transfer from DCM molecules to GNPs increases, leads to quench secondary pulses in the output laser, which generate by oscillation relaxation of population in upper laser level (Fig 4.3) 18 645 (a) 4.00E+015 4.00E+015 (b) 2.00E+015 2.00E+015 0.00E+000 0.00E+000 A16 635 635 A16 A21 640 A21 640 A26 645 A26 645 A31 650 A31 650 4.00E-012 4.00E-012 8.00E-012 8.00E-012 Time (s) Time n(s) GNPs 8x1010 par/ml GNPs 9,5x1010 par/ml 4,00E+015 times above threshold DCM =1X10-3 M (c) 2,00E+015 0,00E+000 635 640 645 650 4,00E-012 8,00E-012 Time (s) GNPs 1,1x1010 par/ml Fig 4.3: Procedue of laser emission spectrum according to the change of GNPs concentration at the pumping rate larger times of the threshold 4.2 Distribute feedback dye laser adjusting wavelengths (DFDL) 4.2.1 Experimental configuration of DFDL To post amplification Nd:YAG laser 532 nm, 10 Hz, 5.6 ns To multipass amplifier 160 J BS M6 L2 M CM M L4 M5 M1 L3 M M M7 M C2 M1 M M2 M2 M M C3 M 560 – 610 nm 12 ps, mJ M M5 M3 DC M4 Fig 4.8: Scheme of a distributed feedback dye laser: Oscillater, Amplification with six passed times and Power amplification 19 4.2.2 Configuration of the wavelength control The wavelength control unit consists of an electronic system connected to a computer for controlling step motor through a pair of conducting bars, that rotates mirrors to adjust the wavelength selection Motor performance is controled by the software of the computer 4.2.3 Experimental results 4.2.3.1 Pulse width Experimental approaches of the influence of the doped-GNPs concentration in the laser medium on the laser pulse width are shown in Fig 4.10 Two shoulders in the autocorrelation trace of the laser pulse were observed when the active laser medium without GNPs and low concentration of GNP were used This shows that there is an overlap of the secondry pulses in the autocorrelation trace a) Intensity (normalized) 1.0 0.5 0.5 0.0 0.0 b) 1.0 30 60 30 60 30 60 1.0 1.0 c) d) 0.5 0.5 0.0 0.0 30 60 Delay time (ps) Fig 4.10: Autocorrelation spots of intensity of laser pulses concentration of GNPs: (a) 2.5×109 particles/cm3, (b) 5×109 particles/cm3, (c) 1×1010 particles/cm3 and (d) 2.5×1010 particles/cm3 20 With increase of the GNPs concentration up to 2.5×1010 particles/mL, there was observed a narrower pulse and the secondary pulses was quenched Finaly, a single pulse corresponding to the concentration of 2.5×1010 particles/mL has been obtained 4.2.3.2 The investigation of laser intensity vs GNPs concentration The peak laser intensity with different GNPs concentration in the active medium of DCM/PMMA is presented in Fig 4.12 0.6 0.2 0.0 Intensity (a.u) 0.4 laser (a.u) độ đỉnhintensity(a.u.) Cường lasser Peak 1.0 2x10 5x10 10 1x10 10 1.5x10 10 2x10 Cường độ (a.u) 5 600 620 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 640 0.00E+000 Bước sóng (nm) Wavelength (nm) 1.00E+010 2.00E+010 GNPs concentration (par/ml) Nồng độ GNPs (hạt/mL) Fig 4.12: Intensity of laser emission of DCM at the wavelength of 626 nm with different GNPs concentration With the increase of GNPs concentration, the peak intensity of laser emission at 5×109 particles/cm3 increases to maximal value When GNPs concentration is increased, the laser intensity started decreasing 4.2.3.3 The range of wavelength adjusting It is observed that the adjusting wavelength range of the DCM laser is almost unchanged (590 – 620 nm) when GNPs concentration is ranging from 2.5 × 109 to 2.5 × 1010 particles/cm3 (Fig 4.13) 21 1: GNPs 2: GNPs 3: GNPs 4: GNPs Normalized Intensity 1,0 2,5x109 par/ml 5x109 par/ml 1x1010 par/ml 2,5x1010 par/ml 0,5 0,0 570 580 590 600 610 620 630 640 Wavelength (nm) Fig 4.13: Range of adjusting laser wavelength with use of GNPs-doped DCM CONCLUSION The thesis titled “Study of organic dye lasers nanogolddoped active medium for generation of short pulse by distributed feedback lasers” is presented new results of the research in the field of developing active medium for the dye laser doped spherical gold nanoparticle in the polymeric host of PMMA The research on the spectro-temporal evolution of the distributed feedback laser using manufactured active medium The main new contribution are obtained as following: 1.1 Setup a technological process and sucessfully manufacture an dye doped-GNPs active medium in the PMMA The results showed that in order to attain mono-dispersive GNPs in PMMA medium, firstly, it is necessary to remove water from GNPs, and then disperse them in MMA solution contained DCM with desired concentrations Manufactured samples possess a high optical homogenity and limited the damage of the DCM dye centers 22 1.2 Investigated and recorded of the significant optical properties of the hybrid active medium made for dye lasers In detail, the fluorescence intensity and absorption spectra of DCM molecules in PMMA host doped GNPs deacreased with the increase of GNPs concentration, whereas fluorescence lifetime of the DCM molecule was almost unchanged In particular, the fluorescence enhancement was observed when the excittion wavelength near the peak of the absorption spectrum of DCM molecule (about 470 nm) was rather far from the peak of the absorption spectrum of GNPs (namely 530nm) 1.3 Research results showed that the stability of the DFDL laser using active medium of DCM/GNPs/PMMA has been improved due to the high thermal conversion coefficient of GNPs with the thermal controling mechanism by the Peltier cell 1.4 Establishing calculation modelization for the spectro-temporal evolution of the hybrid active medium of solid state DCM/GNPs (weak mobility) Bi-direction energy transfer process between two components is a new theoretical model of the energy transfer in the active medium based on DCM/GNPs 1.5 The study has shown that single picosecond laser pulses of can be detected at a high pumping rate above threshold in a DFDL structure with the active medium of DCM/PMMA/GNPs The secondary pulses were quenched due to the energy transfer from DCM molecules to GNPs, whereas the first pulses were almost not affected 1.6 Experimental results by using the DFDL configurations are rather closed to the theoretically modeling calculations In detail, the width of laser pulse of (122) ps was measured by intensity autocorrelation technique at the length of the active volume of 0.5 cm The tuning 23 wavelength range of DFDL laser was not changed for the active medium of DCM/PMMA/GNPs 1.7 The DFDL laser system using active medium of DCM/GNPs/PMMA, that is able to continuoslly tuning wavelengths controlled by a software written in Labview language was successfully performanced The experimental results showed that this laser system operates with a good stability, a high repeat and high degree of confidence 24 PUBLICATIONS - 03 papers published on international ISI journals: [1] N.T.M AN, N.T.H LIEN, N.D HOANG, and D.Q HOA, “Improving the performance of gold -nanoparticle-doped solid-state dye laser using thermal conversion effect”, Journal of Electronic Materials 47, pp 2237–2240 (2018) SCI Q2 [2] N.T.M An, N.T.H Lien, N.T Nghia, and D.Q Hoa, “Spectral evolution of distributed feedback laser of GNPs doped solid-state dye laser medium”, Jourrnal of Applied Physics 122, pp 133110 (2017) SCI Q2 [3] D Q Hoa, N T H Lien, V T T Duong, V Duong & N T M An, “Optical features of spherical gold nanoparticle-doped solid- state dye laser medium”, Journal of Electronic Materials 45, pp 24842489 (2016) SCI Q2 - 02 papers in the national journals [1] Nghiem Thi Ha Lien, Do Thi Hue, Nguyen Thi My An, Do Quang Hoa, Nguyen Trong Nghia, Tran Hong Nhung, “Biofunctionalization of gold nanoshells monitored by surphase plasmon resonance”, Vietnam Journal of Science and Technology 56, pp 604-611 (2018) [2] Nguyen Thi My An, Nghiem Thi Ha Lien, Vu Duong, Nguyen Thanh Thuy, Do Quang Hoa, “A short pulse, narrow band distributed feedback dye laser using nanoparticle-doped dye solution active medium”, Communications in Physics 24, pp.24-28 (2014) - 07 reports published in Proc Conferences and workshops ... Range of adjusting laser wavelength with use of GNPs -doped DCM CONCLUSION The thesis titled Study of organic dye lasers nanogolddoped active medium for generation of short pulse by distributed feedback. .. 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 CHAPTER OVERVIEW OF THE DYE LASERS, LUMINESCENT... 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