Pulse colliding in a self-mode-locked ring-cavity ti:sapphire laser

A new self-mode-locked ring-cavity Ti:sapphire laser is described that is self-mode locked in both unidirectional and bidirectional operations. We found that clockwise and counterclockwise pulses collide with each other at the Ti:sapphire rod when the laser is mode locked in a bidirectional operation. Spectrum narrowing and pulse broadening were found in bidirectional rather than unidirectional mode-locked operation. This is explained by the performance of a transient grating in the gain medium that restricts oscillation to a narrow spectral range.     

2R optical regenerator in As2Se3 chalcogenide fiber characterized by a frequency-resolved optical gating analysis

We present a detailed analysis of a 2R optical regenerator based on self-phase modulation in As(2)Se(3) chalcogenide glass fiber using frequency-resolved optical gating (FROG). We obtain good agreement between the FROG measurements and theory, and confirm that the output pulses are near-transform limited. We show that two-photon absorption improves the profile of the power transfer function while not degrading the temporal performance.     

Measurement for optical arbitrary waveforms using cross-phase modulation cross-correlation frequency-resolved optical gating in a single-mode fibre

A novel scheme of cross-correlation frequency-resolved optical gating (X-FROG) measurement for optical arbitrary waveforms based on the photo-elastic effect and cross-phase modulation (XPM) effect in a single-mode fibre is proposed. In this scheme, a variable delay is generated in the former part of the single-mode fibre by a uniform lateral pressure, and the XPM effect is achieved in the latter part of the fibre. The proposed scheme is very simple and easy to be realized. The amplitude and phase of optical arbitrary waveform to be measured is retrieved from the X-FROG trace using principal component generalized projects algorithm based on matrix. The impacts of the shape of gate pulse, fibre length, relative intensity between gate pulse and optical arbitrary waveform and the complexity of the optical arbitrary waveform on the accuracy of retrieved amplitude and phase are investigated. Simulation results show that, rectangular pulse is a better gate pulse due to lower errors. The accuracy of measurement is improved with the increase in fibre length, and relative intensity between gate pulse and optical arbitrary waveform. Moreover, this scheme also can be used to measure extremely complex optical arbitrary waveforms.     

Experimental study of the geometric group-delay dispersion in graded-index media

We use the highly sensitive method of spatially coherent white-light interferometry to measure the geometric group-delay dispersion in graded-index media. Our measurements confirm previous analyses that the geometric dispersion produced by off-axis beam propagation is anomalous (negative), hence may be used to eliminate the ubiquitous positive dispersion in optical systems. Fabrication of large index-gradient waveguides optimal for dispersion compensation is discussed.     

Bound states of dispersion-managed solitons in a fiber laser at near zero dispersion

We report on the observation of various bound states of dispersion-managed (DM) solitons in a passively mode-locked erbium-doped fiber ring laser at near zero net cavity group velocity dispersion (GVD). The generated DM solitons are characterized by their Gaussian-like spectral profile with no sidebands, which is distinct from those of the conventional solitons generated in fiber lasers with large net negative cavity GVD, of the parabolic pulses generated in fiber lasers with positive cavity GVD and negligible gain saturation and bandwidth limiting, and of the gain-guided solitons generated in fiber lasers with large positive cavity GVD. Furthermore, bound states of DM solitons with fixed soliton separations are also observed. We show that these bound solitons can function as a unit to form bound states themselves. Numerical simulations verified our experimental observations.     

Operation of a Ti:sapphire laser pumped by a 499-nm green laser

We report, for the first time, to our knowledge, the operation of a tunable Ti:sapphire laser pumped by a third-order Raman XeCl-H(2) laser system at 499 nm with a 60-ns pulse duration. The slope efficiency is 59% for this laser, producing pulses of 20-ns duration. The highest conversion-energy efficiency obtained is 41%, with an output energy of 1.2 mJ. The tuning range for a single set of cavity mirrors is 680-834 nm and is limited mainly by the mirror reflectivity. This study shows that a combined laser system based on a XeCl excimer laser can offer wavelength diversity.     

Complete characterization of optical pulses by real-time spectral interferometry

We demonstrate a simple method for complete characterization (of amplitudes and phases) of short optical pulses, using only a dispersive delay line and an oscilloscope. The technique is based on using a dispersive delay line to stretch the pulses and recording the temporal interference of two delayed replicas of the pulse train. Then, by transforming the time domain interference measurements to spectral interferometry, the spectral intensity and phase of the input pulses are reconstructed, using a Fourier-transform algorithm. In the experimental demonstration, mode-locked fiber laser pulses with durations of approximately 1 ps were characterized with a conventional fast photodetector and an oscilloscope.     

Fluorescence anisotropy by use of optical kerr gating with incoherent laser light

Incoherent fluorescence optical Kerr gating can in principle be used to measure fluorescence anisotropies and determine molecular reorientational times. A novel method for fluorescence anisotropy by use of optical Kerr gating with incoherent laser light is presented. Incoherent optical Kerr signals have been obtained for parallel and perpendicular fluorescence polarization for a 10(-3)-M solution of Rhodamine 6G in ethanol.     

Surface polish characterization of industrial Ti: sapphire laser crystal rods by photopyroelectric scanning imaging

Photopyroelectric scanning imaging of a Ti:sapphire crystal with three different surface polishes was carried out using a novel non-contact experimental configuration. Bulk optical absorption coefficient, surface optical absorptance and theoretically normalized quadrature (Q) signal images were obtained. In addition to growth defects in the crystal, the photothermal Q images revealed variations due to the quality of surface polishes in terms of surface optical absorptance, and thermal resistance and homogeneity of each polish. Purely optical-transmission scanned images exhibited lower sensitivity to the degree of the defective state of the Ti:sapphire rod surface due to polishing. It is concluded that photopyroelectric scanning imaging can be used in the quality control of both crystal growth and surface processing of Ti:sapphire crystals.     

Design and characterization of a femtosecond fluorescence spectrometer based on optical Kerr gating

Design and characterization of a general-purpose spectrometer for recording time-resolved emission spectra of typical fluorescent species is described. The system is based on a high repetition rate amplified Ti : sapphire system, an optical Kerr shutter for gating the emission, and a polychromator plus charge-coupled device (CCD) detection system. Using 1 mm of liquid benzene as the Kerr medium, and optics designed to provide high polarization quality, emission spectra of dilute solutions of solutes with nanosecond lifetimes can be recorded with good signal-to-noise ratios. The current spectrometer uses excitation wavelengths near 390 nm and provides spectra over the wavelength range 400-650 nm with 4 nm resolution and instrument response times of 450 fs (full width at half-maximum, FWHM). Selected applications are described to demonstrate the utility of this instrument.     

Simultaneous operation of a dual-channel optical filter in zero dispersion and low-loss optical fiber windows based on a special double-cavity photonic crystal

In this paper, photonic crystal (PC)-based filters with perfect transmittance and narrow-channels located synchronously in zero dispersion (1300 nm) and low-loss (1550 nm) optical fiber communication windows have been introduced. The results demonstrate the potential of 1D photonic crystals for designing of PC-based optical filters with capability of simultaneous filtration of the second and third optical fiber windows even in the presence of oblique incidence angles of light and for both TE- and TM-waves.     

Efficient pulsed 946-nm laser emission from Nd:YAG pumped by a titanium-doped sapphire laser

Efficient pulsed room-temperature laser emission at 946 nm is obtained from a Nd:YAG rod pumped by a Ti-doped sapphire laser in the free-running mode. Three bonded YAG rods of 3-mm diameter with different Nd concentrations and active lengths were tested. A maximum output energy of 83.5 mJ at 3 Hz was obtained with a slope efficiency of 32.3% in an end-pumping configuration.     

Self-seeding of a pulsed double-grating Ti:sapphire laser oscillator

A self-seeded pulsed double-grating Ti:sapphire laser oscillator consisting of a grazing incidence cavity geometry with a pair of gratings and a standing-wave cavity pumped by a frequency-doubled Nd:YAG laser was developed and characterized. With self-seeding, narrow-linewidth single-longitudinal-mode (SLM) operation and SLM scanning were possible with a reduced lasing threshold, which was desirable for the intended applications.     

Synthesis and optical characterization of copper nanoparticles prepared by laser ablation

The remarkable size-tunable properties of nanoparticles (NPs) make them a hot research topic with applications in a wide range of fields. Hence, copper (Cu) colloidal NPs were prepared using laser ablation (Nd:YAG, 1064 nm, 7 ns, 10 Hz, 6000 pulses) of a copper metal plate at different laser fluences (LFs) in the range of 1–2.5 J cm^?2 in ethylene glycol (EG), at room temperature. Analysis of NPs was carried using different independent techniques such as ultraviolet–visible (UV–vis) spectroscopy; transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. TEM analysis showed that the NPs were spherical with a bimodal distribution and an average particle size of 5 and 16 nm influence of 1.2 J cms^?2, and 9 and 22 nm at 2 J cm^?2. The UV–vis spectra of colloidal NPs revealed the maximum absorbance at around 584 nm, indicating the formation of Cu NPs, which supported using FTIR spectra. Furthermore, the absorption spectra confirmed the metallic nature of Cu NPs. FTIR spectroscopy was utilized to verify information about the NPs surface state and chemical bonds constructed in the atom groups apparent on their surface.     

Demonstration of a 1-W injection-locked continuous-wave titanium:sapphire laser

We report on a 1-W injection-locked cw titanium:sapphire ring laser at 846 nm. Single-frequency operation requires only a few milliwatts of injected power. This relatively simple and inexpensive system can be used for watt-level single-frequency lasers across most of the titanium:sapphire gain region. A brief review of injection-locking theory is given, and conclusions based on this theory indicate ways to improve the performance of the system.     

Tuning of a Ti3+:sapphire laser by an electro-optic beam deflection method

A wavelength-switching method for tuning a self-injection-seeded Ti3+:sapphire laser that uses an electro-optic beam deflection technique is reported. A LiNbO3 prism was employed in a tuning arm of the dual-cavity Ti3+:sapphire laser, and wavelength tuning of approximately 94 pm was attained by altering the deflection angle with the application of an electric field of 10 kV/cm to the prism. The spectral characteristics of the output laser were mainly determined by the diffraction grating in the dual-cavity laser, and the electro-optic prism just behaved as a light-beam deflector for the wavelength tuning purpose. This configuration can allow a simple tuning approach where fast and stable electronic wavelength switching is required in a narrow tuning range, on an order between a few tens of picometers to nanometers, without involving any mechanical movement.     

用飞秒Ti：sapphire激光测定对称型化合物的双光子吸收和上转换荧光

用800nm波长的飞秒Ti:sapphire激光测定了2个对称型噁二唑衍生物2,5-二[4-(2-N,N-二苯氨基苯乙烯基)苯基]-1,3,4-噁二唑(PASPO)与2,5-二[4-{2-N,N-二(4-溴代苯)氨基苯乙烯基]苯基}-1,3,4-噁二唑(BrPASPO)的双光子吸收和双光子激发荧光光谱,其飞秒双光子吸收截面为20.6和9.91GM,双光子泵浦上转换荧光最大波长分别在535和545nm.测定了紫外吸收、荧光光谱,研究了化合物在不同溶剂中的溶致变色效应.化合物PASPO和Br-PASPO在二氯甲烷溶液中的吸收峰分别位于412和403nm,荧光发射峰分别位于511和495nm,荧光量子产率分别为0.73和0.70.     

Experimental study of noise properties of a Ti:sapphire femtosecond laser

The fidelity of a coherent link between optical and microwave frequencies is largely determined by noise processes in a mode-locked femtosecond laser. This work presents an experimental study of the noise properties of a Ti:sapphire femtosecond laser. It includes measurements of pulse repetition rate fluctuations and shot noise exhibited by the Ti:sapphire femtosecond laser. Based on the results of noise measurements, the fractional frequency stability of a microwave signal produced by the femtosecond laser has been evaluated.     

Quantitative characterization of clay dispersion in polypropylene-clay nanocomposites by combined transmission electron microscopy and optical microscopy

This paper presents a novel method to describe the microstructure of polymer/clay nanocomposites quantitatively. Based on the image analyses of transmission electron microscopy (TEM) and optical microscopy micrographs, two parameters, degree of dispersion (χ) and mean interparticle distance per unit volume of clay (λ_V) are proposed to describe the level of clay dispersion. The degree of dispersion gives the percentage of exfoliation, and λ_V is a measure of spatial separation between particles relative to clay loading. A polypropylene/clay system was chosen as an example to show the effects of processing conditions and biaxial stretching on clay dispersion using the proposed quantifiers. It provides insights into the ‘real’ clay dispersion using a combination of both microscopical and macroscopical aspects.     

Detailed performance modeling of a pulsed high-power single-frequency Ti:sapphire laser

Differential absorption lidar (DIAL) is a unique technique for profiling water vapor from the ground up to the lower stratosphere. For accurate measurements, the DIAL laser transmitter has to meet stringent requirements. These include high average power (up to 10 W) and high single-shot pulse energy, a spectral purity >99.9%, a frequency instability <60 MHz rms, and narrow spectral bandwidth (single-mode, <160 MHz). We describe extensive modeling efforts to optimize the resonator design of a Ti:sapphire ring laser in these respects. The simulations were made for the wavelength range of 820 nm, which is optimum for ground-based observations, and for both stable and unstable resonator configurations. The simulator consists of four modules: (1) a thermal module for determining the thermal lensing of the Brewster-cut Ti:sapphire crystal collinear pumped from both ends with a high-power, frequency-doubled Nd:YAG laser; (2) a module for calculating the in-cavity beam propagations for stable and unstable resonators; (3) a performance module for simulating the pumping efficiency and the laser pulse energy; and (4) a spectral module for simulating injection seeding and the spectral properties of the laser radiation including spectral impurity. Both a stable and an unstable Ti:sapphire laser resonator were designed for delivering an average power of 10 W at a pulse repetition frequency of 250 Hz with a pulse length of approximately 40 ns, satisfying all spectral requirements. Although the unstable resonator design is more complex to align and has a higher lasing threshold, it yields similar efficiency and higher spectral purity at higher overall mode volume, which is promising for long-term routine operations.