The interaction of intense femtosecond laser pulses with rare gas clusters was studied experimentally, the time-of-flight spectra of ions from exploding clusters at different gas densities have been measured. It is found that while the relative components of ions in low and high energy of the ion energy spectrum decrease with the increase of the gas density, the average ion energies are the same for different gas densities, which indicates that the effect of gas density on laser-cluster interaction is not important under our experimental conditions.

In optical soliton propagation through a single mode optical fiber, it is established that self-phase modulation is maintained by the third order non-linearity of the silica-based glass material of the fiber. In this paper we show that the fifth order non-linearity has also some contribution in frequency variation of self-phase modulation.

The time and amplitude characteristics of the transient power overshoot caused by channels adding up are studied both experimentally and numerically in the backward-pumped Raman amplified wavelength division multiplexing (WDM) system. The results show that the shorter the signal wavelength is, the smaller the last time of the transient power overshoot will be. The maximal power overshoot is small and does not deadly damage the optical component, and the channel distribution of the maximal value of the power overshoot has similar curve in shape with that of the system ON-OFF gain.

In-line synchronous modulation as a way of mitigating the signal quality degradation induced by polarization mode dispersion (PMD) was experimentally studied using 10-Gb/s return to zero signal. Bit error rate of the degraded signal and the synchronously modulated signal under the differential group delay (DGD) values of 10, 20, 34, and 70 ps was measured and compared. The experimental results showed that in-line synchronous modulation is useful to mitigate the signal quality degeneration induced by PMD. 1-dB power penalty reduction was obtained even when the PMD was as high as 70% of the bit interval. The limitation of method is also discussed.

In this paper, a novel concept of multi-granularity p-cycle is proposed. In conventional p-cycle concept, all on-cycle spans have the same capacity. However, in multi-granularity p-cycle, each on-cycle span could have different capacity. Results show that multi-granularity p-cycles are much more capacity-efficient and cost-effective than conventional p-cycles. We also propose two protection switching schemes for all types of p-cycle networks. One is wrapping protection, in which only two end nodes do real-time switching when a span failure happens. The other is steering protection, in which at most four nodes do real-time switching when a span fails. In steering protection switching scheme, the restoration path for the failure traffic demand has the least hops.

By using orthogonal discrete wavelet transform (ODWT) and generalized cross validation (GCV), and combining with Luck-Richardson algorithm based on Poisson-Markov model (MPML), several new super-resolution image restoration algorithms are proposed. According to simulation experiments for practical images, all the proposed algorithms could retain image details better than MPML, and be more suitable to low signal-to-noise ratio (SNR) images. The single operation wavelet MPML (SW-MPML) algorithm and MPML algorithm based on single operation wavelet transform (MPML-SW) avoid the iterative operation of self-adaptive parameter in MPML particularly, and improve operating speed and precision. They are instantaneous to super-resolution image restoration process and have extensive application foreground.

In this paper a fusion method is proposed for merging a high-resolution panchromatic image and a low-resolution multispectral image. The algorithm is based on discrete wavelet transform (DWT). It uses correlation moment rule to the low frequency bands and local deviation rule to the high frequency bands separately. Experimental results indicate that the proposed approach outperforms the traditional methods.

A position sensor based on slit imaging is proposed and its measurement principle is described. An imaging slit is illuminated by a collimated laser beam with square-wave modulation and imaged on a detection double slit through a 4f system. A magnified image of the detection double slit is formed on a bi-cell detector. The position of the imaging slit is obtained by detecting light intensity on two parts of the bi-cell detector. In experiments, the feasibility of the sensor was verified. The repeatability was less than 40 nm.

The effect of speckle pattern on laser Doppler velocimeters is studied theoretically and experimentally. We have found that dynamic speckle patterns can cause error in velocity measurement. Increasing sampling time and using proper signal processing circuits can eliminate this bad effect caused by speckle pattern. The accuracy of velocity measurement is better than 2.1% in a wide velocity range (4.66-468.86 mm/s) when speckle effects are taken into account.

In order to realize variable contrast in the minimum resolvable contrast (MRC) measuring target in the visible imaging system, a novel technique is presented, which adopts two integrating spheres to illuminate two sides of target respectively and the different contrasts can be achieved by regulating the luminance in two integrating spheres. This technique can make the contrast be regulated more conveniently. Based on this technique, the MRC measuring device is developed. This device can be used in all kinds of trial fields. The expanded uncertainty of measuring MRC is less than 3%.

In the measurement of automobile body-in-white, it has been widely studied to position the two-dimensional (2D) visual sensors with high precision. In this paper a graphic positioning method is proposed, a hollow tetrahedron is used for a positioning target to replace all the edges of a standard automobile body. A 2D visual sensor can be positioned through adjusting two triangles to be superposed on a screen of the computer, so it is very important to evaluate the superposition precision of the two triangles. Several methods are discussed and the least square method is adopted at last, it makes the adjustment more easy and intuitive with high precision.

In conventional rational harmonic mode-locking, optical pulse trains with the repetition rate of (pn+1)f_(c) are generated when the modulation frequency of the in-cavity modulator is set at f_(m)=(n+1/p)f_(c), where n and p are both integers, f_(c) is the fundamental cavity frequency. In this paper, we report that rational harmonic mode locking phenomenon takes place in the fiber lasers when the modulation frequency is set at f_(m)=(n+2/p)f_(c). The pulse generations are experimentally demonstrated when the numerator of the rational corresponds to 2 in 5th and 7th order rational harmonic mode-locking.

A pre-pumped passively Q-switched Nd:YAG/Cr:YAG microchip laser is demonstrated with a peak power of 7.5 kW at pulse repetition rate of serveral kilohertzs. The full-width at half-maximum (FWHM) is 734 ps, and the pulse energy is 5.5 μJ with a fundamental spatial mode. In this system, the pre-pumped microchip laser of Nd:YAG/Cr:YAG wafer which is bonded through the thermal-bonding technique has achieved a time jitter value of 12 μs and a Q-switched amplitude instability of 1.26% (1δ) through the pre-pumped modulation technique.

The effects of main laser parameters, such as pulse energy, pulse duration, frequency, and work time on laser propulsion of "air-breathing mode", are investigated experimentally with a high power and high repetition frequency TEA-CO2 pulsed laser. The results show that the momentum coupling coefficient C_(m) decreases with increasing the pulse energy for single pulse tests and pulse duration of about 1 μs. Either higher or lower frequency will reduce C_(m) in multi-pulse tests, which suggests an optimal frequency for the maximum C_(m). As to the work time, the longer the work time is, the less the C_(m) will be.

A novel fusion bonding method between silicon and glass with Nd:YAG laser is described. This method overcomes the movable mechanical parts damage caused by the electrostatics force in micro-electronic machine-system (MEMS) device during the anodic bonding. The diameter of laser spot is 300 μm, the power of laser is 100 W, the laser velocity for bonding is 0.05 m/s, the average bonding tension is 6.3 MPa. It could distinctly reduce and eliminate the defects and damage, especially in movable sensitive mechanical parts of MEMS device.

Spectral characteristics of the amplified spontaneous emission (ASE) from a novel single mode Er3+ doped tellurite fiber with D-type cladding is reported in this letter. When pumped at 980 nm, an ASE source that has nearly a 100-nm flat FWHM bandwidth is obtained with a fiber length of 30-60 cm. Variation of ASE spectra with pump powers and fiber lengths are measured. Output power up to 2.0 mW is obtained with a launched pump power of 660 mW.

Nd3+-doped tellurite glass and a single mode tellurite glass fiber with a core diameter of 8 μm were prepared in this work. The 1.33-μm emission from the 4F_(3/2)-->4I_(13/2) transition of Nd3+ with a spectral bandwidth of 55 nm in tellurite glass fiber is observed. The lifetime of 164 $\mu $s of 4F_(3/2) level and quantum efficiency of about 100% are obtained.

By utilizing the cross polarization modulation effect in semiconductor optical amplifier (SOA), the extinction ratio of cross gain modulation (XGM) wavelength conversion was enhanced, the pattern effect was significantly reduced, and the power penalty of wavelength conversion was reduced by 5 dB simultaneously. Furthermore, by adjusting the settings of polarization controllers, both inverted and non-inverted wavelength conversion can be achieved right in the same wavelength converter.

This letter describes a novel optical method for wavelength fine-selection in the optical spectrum analysers (OSAs) for dense wavelength division multiplexing (DWDM) applications. The proposed new method employs a 'refractive optical lever' system consisting of a rotating optical wedge prism. A new OSA system based on Littman-type monochromator is proposed and the wavelength selection accuracy and resolution of OSA that has included such an optical lever system have been improved by a factor of 20 to 100 depending on the wedge angle and offset orientation angle of the optical wedge prism. This proposed 'refractive optical lever' may also simplify the rotation mechanism of the mirror in the commercially available OSAs.

Crystallization is induced by pulsed laser irradiation of as-deposited amorphous Ge2Sb2Te5 films. Changes of the irradiated areas have been analyzed with the reflectivity contrast. As laser fluences increasing, the reflectivity contrast increases from 0%-2% to 14%-16%, which indicates the structure of as-deposited films transforms from amorphous to crystalline phases. The process of crystallization driven by the movement and rearrangement of atoms is described. And also the influence of the pulse duration on the threshold of crystallization is discussed, the results show that a lower threshold of crystallization can be produced for as-deposited films irradiated by the laser with short pulse duration. However, by the laser with long pulse duration, crystallization can only be formed with a higher threshold. The crystallization of films by irradiation of laser pulses is studied by Raman spectra.

A novel tunable multi-wavelength fiber ring laser based on semiconductor optical amplifier (SOA) is proposed by using a high-birefringence (Hi-Bi) fiber loop mirror (FLM) as wavelength filter. With this configuration, the wavelength spacing of this laser can be varied by using the different lengths of Hi-Bi fiber. 8 wavelengths spacing on 450 GHz are experimentally obtained with more than 25-dB signal-to-noise ratio (SNR) for each channel using 1.28-m Hi-Bi fiber in Hi-Bi FLM. The output power variation between different channels is measured to be less than 5.9 dB. The linewidth of each channel is compressed from 0.347 to 0.186 nm by 1.5-m unpumped erbium-doped fiber (EDF). Meanwhile, 17 wavelengths spacing on ITU-gird (100 GHz) are also obtained with 5.9-m Hi-Bi fiber in Hi-Bi FLM. All these channels can be tuned together over 0.4 nm.