We investigate the optical bistability (OB) in a duplicated two-level system contained in a ring cavity. The atoms are driven by two orthogonally polarized fields with a relative phase. The OB behavior of such a system can be controlled by the amplitude and the relative phase of the coupling field, and it is possible to switch between bistability and multistability by adjusting the relative phase.

Using the classical Mie scattering theory, we compute the energy density of an arbitrary partial wave (e.g., the nth order) and then determine that the interaction between an incident planar wave and a sphere of radius a is the one between the sphere and those partial waves the order of which satisfies n 6 ka. We also provide a simple expression to describe the diffracted wave in which the angle-dependent functions are employed. The difference between the accurate and the approximate expressions is demonstrated by numerical calculation.

We report a nanosecond-pulse amplification system based on an Yb-doped, 100-\mu m core, rod-type photonic crystal fiber. Up to 10W of average power with pulse energy of 1 mJ and peak power of 450 kWis obtained at the repetition rate of 10 kHz. The high-power nanosecond pulse has a good pulse shape and spectral characteristics. The usage of rod-type fibers provides a novel structure for nanosecond pulse amplification.

An improved optoelectronic oscillator scheme for an optical time division multiplexing (OTDM) system based on cascaded Mach–Zehnder modulator (MZM) and polarization modulator (PolM) is experimentally investigated. The system can simultaneously realize clock recovery and demultiplexing. With the MZM working at peak point to generate return-to-zero-33 optical pulses and the PolM working as an equivalent intensity modulator, a high-quality clock signal with 35-fs timing jitter is extracted from the 160-GBaud OTDM-differential quaternary phase-shift keying signal. Narrow short optical switch gates (4 ps) are also generated to demultiplex 160-GBaud signals to 40-GBaud signals. Error-free performance is achieved with 2.4-dB power penalty in the worst case.

A tunable optical rail is embedded into the cavity of a nonlinear-polarization-rotation (NPR) mode-locked fiber laser to generate a sampling pulse with different repetition frequencies and realize bit-rate-adaptive software synchronous optical sampling. Two ultrashort pulses (20.26677 and 20.22900 MHz) are derived, and a 100-MHz data signal is sampled twice with these pulses based on sum-frequency generation (SFG) in periodically poled lithium niobate (PPLN). The eye diagram is successfully recovered, and an estimated bit rate of 102.22 MHz is derived. This method is feasible for bit rates ranging from 200 MHz to 1 GHz, with <3% relative error.

We propose and demonstrate a photonic approach to instantaneous frequency measurement with an extended range based on phase modulation. In the measurement system, two optical wavelengths and two dispersion fiber segments are used to construct the frequency-dependent amplitude comparison functions (ACFs). Several ACFs can be utilized jointly to determine the microwave frequency without ambiguities beyond a monotonic region of the lone conventional ACF. The measurable range of microwave frequency can be extended and the accuracy can be improved by selecting an ACF with a large slope. The experimental results show that the errors are limited within +(-)140 MHz of a frequency measuremental range from 8 to 20 GHz.

We experimentally investigate an optimum scheme of coupling a collimated light from a Ti:sapphire laser source into a standard single-mode fiber (SMF). By adjusting the effective numerical aperture (NA) of coupling lens and eliminating the chromatic aberration, a coupling efficiency of around 70% is finally obtained. This result is close to the maximum value predicted by theoretical simulation. It is well demonstrated that high coupling efficiency between Ti:sapphire laser and SMF can also be obtained by optimizing certain parameters of a coupling lens, without employing any special optical components, or the specific fiber with complex structure.

A method for fast and low bit-rate compression of digital holograms based on a new vector quantization (VQ) method known as the skip-dimension VQ (SDVQ) is proposed. Briefly, a complex hologram is converted into a real off-axis hologram, and partitioned into a set of image vectors. The image vectors are passed into a graphic processing unit (GPU), and compressed through SDVQ into a set of code indices considerably smaller in data size than the source hologram. Experimental evaluation reveals that our scheme is capable of compressing a digital hologram to a compression ratio of over 500 times, in approximately 20–22 ms.

We demonstrate an end-pumped, c-cut Nd:YVO4 laser that emitted first-order Laguerre-Gaussian (LG01) beam by adjusting the position of focused pump beam relative to laser crystal. The pumping light reached the laser crystal has circular and solid intensity profile. The laser is compact and stable, and the obtained LG01 beam power reaches 202 mW with ~25% slope efficiency.

A novel design for a highly ecient 1-kHz single-frequency green laser is proposed. An ecient single-frequency laser pulse output at 532-nm wavelength may be obtained by combining the injection seeding with intracavity frequency doubling in a compact U-shaped cavity formed by two plano dichroic mirrors in an end-pumping arrangement. The laser is capable of producing green pulses with a total energy of 6.3 mJ at a pulse repetition rate of 1 kHz. The pulse width is about 10 ns and the optical–optical eciency from the 808-nm pump source to the 532-nm green output is around 12.7%.

We investigate the effects of a piece of zero-dispersion fiber (ZDF) on the pulse dynamics of a passively mode-locked fiber laser operating in the stretched-pulse regime. Numerical simulation suggests that the proper location and length of ZDF facilitate spectrum broadening and pulse shortening in fiber lasers while maintaining constant net cavity dispersion. A nonlinear polarization evolution mode-locked Er-doped fiber laser with a dispersion map is built based on the simulation. Larger optical spectrum broadening is obtained by inserting a longer ZDF after the active fiber during single-pulse operation, which well agrees with the simulation.

Yb3+ singly doped and Yb3+/Al3+co-doped high silica glass samples are prepared, and their luminescent properties are investigated. Al3+ is considered as a beneficial activator for Yb3+-doped glass. However, the experimental result shows that the addition of Al3+ results in the transformation from Yb3+ to Yb2+ and the improvement in the photon luminescence of Yb2+. These characteristics indicate the role of Al3+ in Yb3+-doped glass.

An asymmetric metamaterial exhibiting an analog of double electromagnetically induced transparency (EIT) in the middle-infrared region is reported. The metamaterial consists of two-layered arrays of U-shaped rings embedded in a medium, with the lower layer rotated by 90o. Our simulations demonstrate that both maximum group indexes are extremely high at the two EIT-like positions. The group index reaches about thrice the currently reported maximum value at the high-frequency EIT-like position. The transmittance at the two transparency positions also possesses extremely high Q factors, which is conducive to controlling the propagation of electromagnetic waves.

We evaluate the ablation thresholds of Er:YAG and Er,Cr:YSGG laser for enamel and dentin. A total of 140 dental slices is evenly divided into two groups: the dentin group and the enamel group. Dental tissues are irradiated with either an Er:YAG laser or an Er,Cr:YSGG laser with pulse widths in the order of 100 \mu s. The laser fluence is increased gradually until the ablation crater is formed. The laser ablation threshold is calculated using probit analysis. The ablation thresholds of the Er:YAG laser for dentin and enamel range from 2.88 to 3.36 J/cm2 and from 2.94 to 3.8 J/cm2, respectively, and the ablation thresholds of the Er,Cr:YSGG laser for dentin and enamel range from 2.92 to 4.2 J/cm2 and from 4.93 to 5.66 J/cm2, respectively.

A new type of silica optical micro-kayak cavity fabricated on a silicon chip is designed and demonstrated. This micro-kayak cavity with two straight sides and two semi-circle sides can be used to achieve a compact and flexible arrangement in the design of integrated photonic circuits. The micro-kayak cavity can also be embedded with a Bragg reflection grating in the straight sides for frequency selection using a micro-kayak cavity laser doped with a rare-earth ion. We describe the fabrication methods for the micro-kayak cavity, obtain its spectra, and discuss its potential applications.

A special-velocity-matched electro-optic (EO) phase modulator employing a microwave resonant design in lithium niobate is presented. Both the microwave property and phase-modulation performances of the 3.25-GHz modulator agree well with the numerical simulations. Using this modulator in a single-pass configuration with 1-kW microwave drive power, the spectral bandwidth of a 1 053-nm, 3-ns pulse-length laser is broadened to 0.13 nm. With a clear aperture of 5×5 (mm), the modulator is suited for two- dimensional smoothing by spectral dispersion in high power laser systems.

We present a method of both polarization and amplitude modulations on an incident beam to obtain a longitudinally polarized subwavelength-sized optical needle. A 4-f system with a spatial light modulator is used to generate experimentally a two-mode alternate cylindrical vector beam by polarization modulation, enhancing performance and facilitating implementation. We optimize the beam focusing properties after passing the beam through an annular aperture to obtain amplitude modulation by the simulated annealing algorithm. Numerical results indicate that a sharp focal spot (0.417\lambda) with a long focal depth (8\lambda) and a strong longitudinally polarized field can be easily achieved.

Noninvasive technology for measuring instantaneously two-dimensional (2D) temperature distributions of flame using two-color planar laser induced fluorescence (PLIF) of OH is investigated. A calibration method is researched and developed. This method is based on the calibration experiments with a laminar premixed flame and thermocouple, and avoids complex calculation and uncertainty of the spectrum parameters. Measurements for a flat burner at ambient temperature under atmospheric pressure are also presented; calibration results are used to diagnose a supersonic combustion in scramjet combustor. The conclusion indicates that this method is useful, and a better precision of calibration can be acquired by correcting the line shapes of the spectral lines and lasers.

Repetition rate-dependent absorbance measurements of synthetic fused silica at 193-nm irradiation are performed in the range of 50–1 000 Hz with an ArF laser calorimeter. The "apparent" single- and twophoton absorption coefficients are determined by measuring the laser fluence-dependent absorbance of fused silica samples with different thicknesses to separate the surface absorption and bulk absorption. The measurement results indicate a reversible nonlinear increase of both apparent single- and two-photon absorption coefficients with increasing repetition rate for the synthetic fused silica, whereas the surface absorption shows no dependence on the repetition rate.

We propose a new Fourier transform spectrometer based on programmable microelectromechanical systems (MEMS) micro-mirror and an improved Michelson interferometer. The principle of the spectrometer is theoretically analyzed. A signal acquisition unit and an experimental set-up are designed. The spectrum of the polychromatic light source is obtained at a slantwise reflector angle of 0.238o. The spectrum is analyzed by this system within the near infrared. The experimental results show that the spectral accuracy is less than 3 nm, and the signal-to-noise ratio (SNR) is 18 dB. The spectral resolution is less than 16 nm.

Laser-induced breakdown spectroscopy (LIBS) is used to determine the total nitrogen (TN) and total phosphorus (TP) in soil. Quantitative determinations are conducted using the line intensity of the analyte element and element concentration. Calibration models are obtained using ten samples for TN and seven samples for TP. The rest samples are used to validate the results. Strong linear correlations are obtained from the determined TN and TP concentrations. LIBS is a powerful tool for analyzing soil samples to determine nutrient elements by selecting calibration and validation samples with similar matrix composition.