Passively Mode-Locked Er-Doped Fiber Laser Based on Sb2S3-PVA Saturable Absorber

In this paper, antimony trisulfide (Sb₂S₃) was successfully prepared with the liquid phase exfoliation method and embedded into polyvinyl alcohol (PVA) as a saturable absorber (SA) in a passively mode-locked Er-doped fiber laser for the first time. Based on Sb₂S₃-PVA SA with a modulation depth of 4.0% and a saturable intensity of 1.545 GW/cm², a maximum average output power of 3.04 mW and maximum peak power of 325.6 W for the stable mode-locked pulses was achieved with slope a efficiency of 0.87% and maximum single pulse energy of 0.81 nJ at a repetition rate of 3.47 MHz under a pump power of 369 mW. A minimum pulse width value of 2.4 ps with a variation range less than 0.1 ps, and a maximum signal to noise ratio (SNR) of 54.3 dB indicated reliable stability of mode-locking, revealing promising potentials of Sb₂S₃ as a saturable absorber in ultrafast all-fiber lasers.     

Generation of High Peak Power Mode-Locked Green Pulses Based on WS2 and EOM: Experiment and Theory

Based on an as-prepared high-quality WS₂ film and an electro-optic modulator (EOM), a dual-loss-modulated low repetition rate mode-locking laser at 0.53 μm with high peak power is presented for the first time. The laser characteristics versus the pump power are investigated experimentally and theoretically. At a pump power of 10.67 W, the shortest pulse duration of 305 ps can be measured, corresponding to the highest peak power of 931 kW, which is much higher than those of the single passive modulated lasers with WS₂-SA. A simple rate equation simulation was used to describe this dual-loss-modulated mode-locking green laser based on WS₂ and EOM. The results of the numerical simulation are basically in accordance with the experimental values.     

Experimental and Theoretical Study of an Actively Q-Switched Tm:YLF Laser with an Acousto-Optic Modulator

We report the characteristics of a diode-end-pumped, high-repetition-rate, acoustic-optic (AO) Q-switched Tm:YLF laser operating from 5 kHz to 10 kHz. In the continuous-wave (CW) regime, a maximum average output power of 8.5 W was obtained with a slope efficiency of 30.7%. Under the AO Q-switching regime, a maximum output power of 7.32 W was obtained at a repetition frequency of 5 kHz with a pulse width of 68 ns and a pulse energy of 1.4 mJ, corresponding to a peak power of 21.5 kW. A time-dependent rate equation model is introduced to theoretically analyze the results obtained in the experiment, in which the cross-relaxation phenomenon, upconversion losses and ground-state depletion are taken into account. Additionally, the evolution processes of population inversion density and intracavity photon number density with time are also presented. The theoretical results well predict the dependence of laser output characteristics of Tm:YLF crystal on the incident pump powers.     

Synthesis and laser application of the dithiolene nickel complex compounds

A series of dithiolene nickel complex compounds with a general formula (RCSCSR′)₂Ni that have an intense absorption band in near-IR region were successfully synthesized and the maximum IR absorption wavelengths of these dyes vary from 875 to 1495 nm in different solvents. Their characteristics of Q-switching and mode-locking for different lasers were investigated. Q-switched 1064 and 1079 nm laser with a polymer film or organic solution work satisfactorily and the pulse widths are 4–10 ns. The dyes in a variety of solutions show excellent properties in mode-locking the 1079 nm laser, particularly in mode-locking the 1340 nm laser. The pulse widths are 90–120 ps. The experimental results show that the choice of different ring substitutes and solvents will greatly influence the corresponding dye laser properties. It is also implied that BDN16 and BDN17 as the mode-locking dyes for the 1500 nm laser are satisfactory.     

The Investigation on Ultrafast Pulse Formation in a Tm–Ho-Codoped Mode-Locking Fiber Oscillator

We experimentally investigate the formation of various pulses from a thulium–holmium (Tm–Ho)-codoped nonlinear polarization rotation (NPR) mode-locking fiber oscillator. The ultrafast fiber oscillator can simultaneously operate in the noise-like and soliton mode-locking regimes with two different emission wavelengths located around 1947 and 2010 nm, which are believed to be induced from the laser transition of Tm³⁺ and Ho³⁺ ions respectively. When the noise-like pulse (NLP) and soliton pulse (SP) co-exist inside the laser oscillator, a maximum output power of 295 mW is achieved with a pulse repetition rate of 19.85-MHz, corresponding to a total single pulse energy of 14.86 nJ. By adjusting the wave plates, the fiber oscillator could also deliver the dual-NLPs or dual-SPs at dual wavelengths, or single NLP and single SP at one wavelength. The highest 61-order harmonic soliton pulse and 33.4-nJ-NLP are also realized respectively with proper design of the fiber cavity.     

Investigation of Nonlinear Optical Modulation Characteristics of MXene VCrC for Pulsed Lasers

We report the surface morphology and the nonlinear absorption characteristics of MXene VCrC nanosheets prepared by the liquid-phase exfoliation method. The self-made MXene VCrC was applied as a saturable absorber in the Tm:YAP laser experiments, performing excellent Q-switching optical modulation characteristics in infrared range. With this absorber, a stable passively Q-switched 2 μm laser was achieved. Under an incident pump power of 3.52 W, a maximum output power of 280 mW was obtained with a T = 3% output coupler at a repetition frequency of 49 kHz. The corresponding pulse energy and peak power were 5.7 μJ and 6.6 W, respectively. The shortest pulse duration was 658 ns at the repetition rate of 63 kHz with a T = 1% output coupler.     

Synthesis of silver nanoparticles for remote opening of polyelectrolyte microcapsules

Silver nanoparticles of 10, 18, and 23 nm were synthesized in aqueous medium by chemical reduction of silver nitrate in excess of sodium borohydride. Modification of polyelectrolyte shells with synthesized silver nanoparticles was performed using the layer-by-layer approach. Remote opening of the polyelectrolyte/silver capsules was performed with a CW Nd:YAG FD laser with an average incident power output up to 70 mW. Capsules with a mixture of 10 and 18 nm silver nanoparticles in its polyelectrolyte shell were ruptured after less than 7 s of laser irradiation, while microcapsules with 23 nm silver nanoparticles in the shell were broken after 11 s of laser treatment and 10 nm silver nanoparticles were broken after 26 s.     

Visible fluorescence spectrometry using second harmonic emission self-induced in semiconductor laser as a light source

Second harmonic emission (416 or 453 nm) self-induced in a nearinfrared semiconductor laser (832 or 906 nm) is used as a light source for excitation of the fluorescent molecules which have absorption bands in the visible region. The conversion efficiency from fundamental to second harmonic emission is 1.7 × 10^–11 (0.5 pW) for a continuous wave (CW) laser, when it is operated at 30 mW. This value is further improved for a pulsed laser operated at a peak power of 10 W. Perylene is used as a standard sample for construction of an analytical curve. The detection limit is 10^–6 M for CW laser excitation. The present fluorimetric system is used for measurements of pH dependence of the fluorescence intensity for 8-hydroxy-1,3,6-pyrenetrisulfonic acid (HPTS). Neutralization titration is demonstrated by using HPTS as a pH indicator.     

Pressure and laser intensity effects on kinetic rates in binary reactive gas mixtures

The irradiation of binary reactive gaseous mixture by a CW CO₂ laser at changing pressure of absorber or transparent reactant have been performed at over-all pressures of several hundreds torrs with a maximum laser intensity of 680 W.cm⁻². A radial thermodiffusion effect leading both to a transient depletion of absorber concentration in the irradiation zone and a decrease of the rate of decomposition have been shown. The maximum yield of decomposition which appears at a given intensity and pressure of absorber when the pressure of reactant is changed is general for the binary gas mixtures tested ; it may be understood in terms of laser energy deposited in the mixture and distributed between the absorber and reactant partners. A rate decomposition dependent on the square of incident laser intensity and proceeding from this distribution is also exhibited.     

Line patterning of (Sr,Ba)Nb2O6 crystals in borate glasses by transition metal atom heat processing

Some NiO-doped Bi₂O₃,La₂O₃-SrO-BaO-Nb₂O₅-B₂O₃ glasses giving the formation of strontium barium niobate Sr_0.5Ba_0.5Nb₂O₆ (SBN) crystals with a tetragonal tungsten-bronze structure through conventional crystallization in an electric furnace have been developed, and SBN crystal lines have been patterned on the glass surface by heat-assisted (250-300 °C) laser irradiation and scanning of continuous-wave Nd:YAG laser (wavelength: 1064 nm). The surface morphology and the quality of SBN crystal lines are examined from measurements of confocal scanning laser micrographs and polarized micro-Raman scattering spectra. The surface morphology of SBN crystal lines changes from periodic bump structures to homogeneous structures, depending on laser scanning conditions. It is suggested that the line patterned at the laser irradiation condition of laser power P=1 W and of laser scanning speed S=1 μm/s in 2NiO-4La₂O₃-16SrO-16BaO-32Nb₂O₅-30B₂O₃ glass has a possibility of the orientation of SBN crystals along the laser scanning direction. The present study demonstrates that the transition metal atom heat processing (i.e., a combination of cw Nd:YAG laser and Ni²⁺ ions) is a novel technique for spatially selected crystallization of SBN crystals in glass.     

Sampling modulation technique in radio-frequency helium glow discharge emission source by use of pulsed laser ablation

An emission excitation source comprising a high-frequency diode-pumped Q-switched Nd:YAG laser and a radio-frequency powered glow discharge lamp is proposed. In this system sample atoms ablated by the laser irradiation are introduced into the lamp chamber and subsequently excited by the helium glow discharge plasma. The pulsed operation of the laser can produce a cyclic variation in the emission intensities of the sample atoms whereas the plasma gas species emit the radiation continuously. The salient feature of the proposed technique is the selective detection of the laser modulation signal from the rest of the continuous background emissions, which can be achieved with the phase sensitive detection of the lock-in amplifier. The arrangement may be used to estimate the emission intensity of the laser ablated atom, free from the interference of other species present in the plasma. The experiments were conducted with a 13.56 MHz radio-frequency (rf) generator operated at 80 W power to produce plasma and the laser at a wavelength of 1064 nm (pulse duration:34 ns, repetition rate:7 kHz and average pulse energy of about 0.36 mJ) was employed for sample ablation. The measurements resulted in almost complete removal of nitrogen molecular bands (N₂⁺ 391.44 nm). Considerable reduction (about 75%) in the emission intensity of a carbon atomic line (C I 193.03 nm) was also observed.     

Development of a multi-frequency laser for use in MALDI-TOFMS

The application of a multi-frequency laser source for the use in matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) is described. An elliptically polarized beam of a Nd:YAG laser emitting at 355 nm (200 mJ) is focused into a Raman shifter, filled with high pressure hydrogen. As a result, numerous Raman lasers (including vibrational and rotational Raman emissions for hydrogen; 4155 and 587 cm⁻¹ shifts, respectively) were generated with a total power of ∼100 mJ. Using this multi-frequency laser as an ionization source, methionine enkephalin (MW 573.7), angiotensin I (MW 1296.5) and oxidized insulin chain B (MW 3495.9) were examined, as model compounds using α-cyano-4-hydroxycinnamic acid (CHCA), sinapinic acid (SA) and activated charcoal as the matrix, respectively. As a result, the S/N ratios were improved when the multi-frequency laser was used, compared to the single light source of the Nd:YAG laser (355 nm), irrespective of the type of matrix used. This is because the multi-frequency laser provides multi-line for absorption, where the traditional N₂ laser only provides single wavelength (at 337 nm) for absorption.     

Lasers used in analytical micropyrolysis

Laser micropyrolysis gas chromatography mass spectrometry (GC-MS) allows analytical pyrolysis to be conducted with micro-spatial resolution. Despite the large range of contemporary laser sources, most previous laser pyrolysis studies have been conducted with continuous wave (CW) infrared irradiation. Here, the laser micropyrolysis analysis of a Sydney torbanite was conducted with three different laser sources - 1. CW 532 nm; 2. Q-Switched (QSw) pulsed 1064 nm; and 3. QSw pulsed 266 nm - to compare the molecular analyses attributes of different laser types (λ: 266-1064 nm; CW or QSw). The CW 532 nm laser irradiation consistently produced high concentrations of n-hydrocarbons, with lesser amounts of cyclic and aromatic hydrocarbons, similar to previous analyses with both CW 1064 nm laser pyrolysis and conventional analytical pyrolysis [1]. In contrast, both the IR and UV QSw pulsed irradiation sources provided poor and varied data. Relatively low concentrations of n-hydrocarbons were occasionally produced, but most often no structurally significant products were detected. The poor maintenance of hydrocarbon structural units by the short pulse lasers can be attributed to the very high power density delivered, leading to excessive degradation of the irradiated macromolecule.     

延时提取正交发射MALDI技术研究

An orthogonal injection (OI) home-made reflectror type time-of-flight (TOF) mass spectrometer has been constructed with a matrix-assisted laser desorption/ionization (MALDI) source. Ions generated by MALDI are measured using a pulsed voltage delayed extraction method. The laser used is a frequency quadrupled Nd:YAG laser with output at wavelength of 266 nm, the matrix used here is 2,5-dihydroxybenzonic acid (DHB), and the analytes are Malachite green and peptides. Measurements of resolving power and statistical evaluation of the mass accuracy are reported here. The results indicate that resolving power in the range of 3400 to 4000 (full width at half maximum), the average error of the mass accuracy is below 0.0075%, A perfectly linear (m/z)1/2 versus t plot is found. Finally, the initial velocity distribution of analyte and matrix ions in the range of 400~1000 m/s is measured.     

Non-linear effects by continuous wave cavity ringdown spectroscopy in jet-cooled NO2

A new method of high resolution cavity ringdown spectroscopy (CRDS) was recently developed in our laboratory, where a narrow line, continuous wave (CW) single-frequency laser is used instead of a pulsed laser. Here, we will first discuss the main differences between the `traditional' pulsed CRDS and CW-CRDS. Then, we will describe our results exploiting the high intracavity power that can be achieved with CW-CRDS. Using a single-mode Ti:Sa laser, we obtained CRDS spectra where the excitation power of a single cavity mode is close to 20 W. In the virtually collisionless regime of a supersonic slit jet, we observed saturation in some of the weak rovibronic transitions of NO₂ around 796 nm, as evidenced by loss of absorption intensity and formation of Doppler-free Lamb dips. In addition, in coincidence with absorption by these near infrared transitions, an appreciable fluorescence signal was detected in the visible range. According to our interpretation, this fluorescence is from NO₂ levels excited by two photons in a stepwise incoherent process, with a strongly allowed second step. Since the fluorescence spectrum has the same lineshapes as the CRDS absorption spectrum, it seems that the first transition step is the one limiting the overall two-step process. In addition, we also observed very narrow fluorescence features, not coincident with any absorption feature. These must be coherent (non-stepwise), Doppler-free, two-photon transitions. Interesting new questions arise from these preliminary data, and we believe that more measurements of this kind will provide new information about the rovibronic states of NO₂ in the dissociation region.     

Formation of nonlinear optical KSm(PO3)4 crystals in phosphate glasses by YAG laser irradiation

Some glasses such as 15K₂O·15Sm₂O₃·70P₂O₅ giving the formation of the nonlinear optical KSm(PO₃)₄ phase through the usual crystallization in an electric furnace and through Nd:YAG laser (1064 nm) irradiation have been developed. The crystallization of the KSm(PO₃)₄ phase showing a second harmonic generation (SHG) is confirmed from X-ray diffraction analysis and micro-Raman scattering spectra. The lines consisting of the KSm(PO₃)₄ phase are constructed by YAG laser irradiation with a power of 0.8 W and a moving speed of 0.5 μm s⁻¹. It is suggested that the crystal growth rate of KSm(PO₃)₄ during laser irradiation is extremely low. The micro-photoluminescence spectra for Sm³⁺ in the crystal lines show the Stark splitting and large intensities compared with the glass part. It is demonstrated that the samarium atom heat processing is effective in the spatially selected crystallization even in phosphate glasses.     

Energy transfer distributed feedback dye laser using Rhodamine B-Acid blue 7 dye mixture

The characteristics of energy transfer distributed feedback dye laser (ETDFDL) are studied both theoretically and experimentally in a mixture of Rhodamine B and Acid blue 7 dyes pumped by 532 nm Nd:YAG laser. The behaviour of donor and acceptor DFDL, the dependence of their pulse width and output power on pump power and donor-acceptor concentrations are studied. Experimentally, the tunability is achieved over the spectral range 565-680 nm using a prism dye cell arrangement. The output energy of DFDL is measured at the emission peaks of donor and acceptor for different pump powers and donor-acceptor concentrations. The output pulse of DFDL is found to be as narrow as 40-ps duration, which is nearly 100-fold shorter than the pump pulse. The pulse linewidth is of the order of 0.1 A.     

Features of Laser-Induced Modification of Sclera and Cornea

Results are presented from studying collagen degradation in scleral and corneal tissues upon CW IR laser irradiation at a wavelength of 1.56 μm and powers of 1.4 and 7 W. The exposure time is such that the radiometrically determined maximum tissue temperature ranges from 55 to 70°C. It is shown that at a power of 1.4 W, laser-induced collagen denaturation in sclera and cornea starts at 55 and 60°C, respectively. When the power is increased to 7 W, the temperature of denaturation onset rises by 2°C. These findings are discussed from the viewpoint of the joint photothermal and photomechanical effects of laser irradiation.     

Comparison of the effects of visible femtosecond laser pulses and continuous wave laser radiation of low average intensity on the clonogenicity of Escherichia coli

To evaluate the contribution of local pulsed heating of light-absorbing microregions to biochemical activity, irradiation of Escherichia coli was carried out using femtosecond laser pulses (λ = 620 nm, τ_p=3 × 10⁻¹³ s, f_p = 0.5 Hz, E_p = 1.1 × 10⁻³J cm⁻², I_av = 5.5 × 10⁻⁴ W cm⁻², I_p = 10⁹ W cm⁻²) and continuous wave (CW) laser radiation (λ = 632.8 nm, I = 1.3 W cm⁻²). The irradiation dose required to produce a similar biological effect (a 160%–190% increase in the clonogenic activity of the irradiated cells compared with the non-irradiated controls) is a factor of about 10³ lower for pulsed radiation than for CW radiation (3.3 × 10⁻¹ and 7.8 × 10² J cm⁻² respectively). The minimum size of the microregions transiently heated on irradiation with femtosecond laser pulses is estimated to be about 10 Å, which corresponds to the size of the chromophores of hypothetical primary photoacceptors—respiratory chain components.     

From green algae to calcium inside buckyballs

Coorongite and carbonaceous residues from coorongite pyrolysis at 450 and 500°C were studied by laser ablation Fourier transform mass spectrometry. Raw coorongite gave positive-ion spectra having mainly protonated species of m/z 80–300 when laser ablated with a high laser power density. Endohedral fullerene positive ions of calcium were observed during the laser ablation of coorongite pyrolysis residues. Pyrolysis of the raw coorongite at 450 and 500°C produced residues which on laser ablation using the fundamental frequency of an Nd: YAG laser (1064 nm) gave a series of calcium fullerides. These ions were observed using low laser power densities (100–600 kW cm^–2) Mixing the coorongite pyrolysis residue with barium sulphate gave M@C_n⁺ ions

1 The symbol ‘@’, as in Ca@₆₀, is used to represent an endohedral complex, i.e. the adduct is located inside the carbon cage.

where M = calcium or barium. Mixing the coorongite pyrolysis residue with strontium oxalate also gave M@C_n⁺ ions where M = calcium or strontium. No ions containing two or more metals were detected.