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A novel phase-sensitive scanning near-field optical microscope

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Chinese Physics B 2015年第5期24卷 346-351页

作者：武晓宇孙琳谭峭峰王佳 Department of precision instruments State Key Laboratory of Precision Measurement Technology and InstrumentsTsinghua University

Phase is one of the most important parameters of electromagnetic waves. It is the phase distribution that determines the propagation, reflection, refraction, focusing, divergence, and coupling features of light, and further affects the intensity distribution. In recent years, the designs of surface plasmon polariton （SPP） devices have mostly been based on the phase modulation and manipulation. Here we demonstrate a phase sensitive multi-parameter heterodyne scanning near-field opti- cal microscope （SNOM） with an aperture probe in the visible range, with which the near field optical phase and amplitude distributions can be simultaneously obtained. A novel architecture combining a spatial optical path and a fiber optical path is employed for stability and flexibility. Two kinds of typical nano-photonic devices are tested with the system. With the phase-sensitive SNOM, the phase and amplitude distributions of any nano-optical field and localized field generated with any SPP nano-structures and irregular phase modulation surfaces can be investigated. The phase distribution and the interference pattern will help us to gain a better understanding of how light interacts with SPP structures and how SPP waves generate, localize, convert, and propagate on an SPP surface. This will be a significant guidance on SPP nano-structure design and optimization.

关键词： phase detection scanning near-field optical microscope (SNOM) heterodyne interferometry surface plasmon polariton (SPP) devices

Artificial spectral filtering in dissipative soliton fiber lasers with invisible bandpass filters

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Chinese Physics B 2012年第9期21卷 309-314页

作者：孔令杰肖晓晟杨昌喜 state key laboratory of precision Measurement technology and instruments Department of Precision InstrumentsTsinghua University

We numerically study the artificial spectral-filtering effect in dissipative soliton fiber lasers without intracavity spectral filters. It is found that in dissipative soliton lasers with real saturable absorbers （SAs）, the dynamic spectral filtering of the real SAs serves as an artificial spectral filter and contributes to the pulse shaping. While in the dissi- pative soliton lasers with artificiM SAs, such as nonlinear polarization rotation, the spectrM filtering introduced by the intracavity polarization-dependent components acts as an artificial spectral filter and shapes the pulses to obtain mode- locking. An investigation of the artificial spectral-filtering effect reveals the operating mechanisms of the dissipative soliton fiber lasers without visible bandpass filters.

关键词： fiber laser mode locking

External-cavity birefringence feedback effects of microchip Nd:YAG laser and its application in angle measurement

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Chinese Physics B 2009年第8期18卷 3438-3443页

作者：任成谈宜东张书练 state key laboratory of precision Measurement technology and instruments Department of Precision Instruments & MechanologyTsinghua University

External-cavity birefringence feedback effects of the microchip Nd：YAG laser are presented. When a birefringence element is placed in the external feedback cavity of the laser, two orthogonally polarized laser beams with a phase difference are output. The phase difference is twice as large as the phase retardation in the external cavity along the two orthogonal directions. The variable extra-cavity birefringence, caused by rotation of the external-cavity birefringenee element, results in tunable phase difference between the two orthogonally polarized beams. This means that the roll angle information has been translated to phase difference of two output laser beams. A theoretical analysis based on the Fabry-Perot cavity equivalent model and refractive index ellipsoid is presented, which is in good agreement with the experimental results. This phenomenon has potential applications for roll angle measurement.

关键词： microchip laser external-cavity birefringence feedback orthogonally polarized lasers angle measurement

Uncertainty reevaluation in determining the volume of a silicon sphere by spherical harmonics in an Avogadro project

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Chinese Physics B 2011年第9期20卷 152-158页

作者：张继涛吴学健李岩 state key laboratory of precision Measurement technology & instruments Department of Precision Instruments and MechanologyTsinghua University

To determine the Avogadro constant with a target relative uncertainty of 2 x 10-s, the uncertainty component of the silicon sphere＇s volume introduced by the spherical harmonics method, which is usually used in determining the sphere＇s volume, is reevaluated. By means of representing the shape of the silicon sphere by an ellipsoid with Gaussian white noise in its diameters, the uncertainty of the current mapping methods based on the spherical harmonics theory can be estimated theoretically. It is evidenced that the uncertainty component attributed to the current mapping method is underestimated. To eliminate this effect as much as possible, the number of mapping points should be increased to more than before. Moreover, a new mapping method is proposed to accomplish the equal-area mapping with large number points on the silicon sphere.

关键词： metrology Avogadro constant silicon sphere spherical harmonics

Passive harmonic mode locked all-normal-dispersion Yb-doped fibre lasers

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Chinese Physics B 2011年第2期20卷 270-274页

作者：孔令杰肖晓晟杨昌喜 state key laboratory of precision Measurement technology and instruments Department of Precision InstrumentsTsinghua University

Passive harmonic mode-locking of dissipative solitons is demonstrated in all-normal dispersion Yb-doped fibre lasers.A difference equation model of the mode-locked fibre lasers is adopted to simulate the intra-cavity nonlinear *** phenomena around the mode-locking threshold,and the effect of introducing linear phase bias are *** passive harmonic mode-locking as one kind of multipulsing operations is ***,the simulation shows the bistability between multipulsing and single-pulse or period multiplication.

关键词： fibre laser mode-locking ytterbium

Low-repetition-rate, all-polarization-maintaining Yb-doped fiber laser mode-locked by a semiconductor saturable absorber

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Chinese Physics B 2017年第11期26卷 216-220页

作者：肖晓晟 state key laboratory of precision Measurement technology and instruments Department of Precision InstrumentsTsinghua University

A low-repetition-rate, all-polarization-maintaining（PM）-fiber sub-nanosecond oscillator is presented, which is simple and low-cost, composed of standard components. The ring cavity is elongated by 114-m-long standard PM fiber, and passively mode-locked by a fiber pigtailed semiconductor saturable absorber. Linearly polarized pulses with 1.66 MHz repetition rate and 22 dB polarization extinction ratio are generated at a wavelength of 1030 nm, which is determined by an intracavity filter. In addition, to demonstrate that the oscillator is a good seed for high energy pulse generation, an all-fiber master oscillator power amplifier is built and amplified pulses with energy about 2 μJ are obtained.

关键词： mode-locked fiber laser polarization maintaining master oscillator power amplifier

Time-division multiplexing holographic display using angular-spectrum layer-oriented method(Invited Paper)

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Chinese Optics Letters 2016年第1期14卷 16-20页

作者：赵燕曹良才张浩谭巍吴圣函王崝杨强金国藩 state key laboratory of precision Measurement technology and instruments Department of Precision Instruments Tsinghua University

A time-division multiplexing method for computer-generated holograms （CGHs） is proposed to solve the problem of the limited space-bandwidth product. A three-dimensional （3-D） scene is divided into multiple layers at different depths. The CGH corresponding to each layer is calculated by an angular-spectrum algorithm that is effective at a wide range of propagation distances. All of the CGHs are combined into several group-CGHs. These group-CGHs are sequentially uploaded onto one spatial light modulator at a high frame rate. The spacebandwidth product can be benefited by the time-division processing of the CGHs. The proposed method provides a new approach to achieve high quality 3-D display with a fast and accurate CGH computation.

关键词： Bandwidth Holograms Holographic displays Light modulators Multiplexing Spectrum analysis Time division multiplexing

Non-contact angle measurement based on parallel multiplex laser feedback interferometry

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Chinese Physics B 2014年第11期23卷 320-324页

作者：张松谈宜东张书练 state key laboratory of precision Measurement technology and instruments Department of Precision InstrumentsTsinghua University

We present a novel precise angle measurement scheme based on parallel multiplex laser feedback interferometry （PLFI）, which outputs two parallel laser beams and thus their displacement difference reflects the angle variation of the target. Due to its ultrahigh sensitivity to the feedback light, PLFI realizes the direct non-contact measurement of non- cooperative targets. Experimental results show that PLFI has an accuracy of 8＂ within a range of 1400＂. The yaw of a guide is also measured and the experimental results agree with those of the dual-frequency laser interferometer Agilent 5529A.

关键词： laser feedback angle measurement non-cooperative targets

All-normal-dispersion Yb-doped mode-locked fibre laser and its stability analysis

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Chinese Physics B 2010年第7期19卷 308-312页

作者：孔令杰肖晓晟杨昌喜 state key laboratory of precision Measurement technology and instruments Department of Precision InstrumentsTsinghua University

We experimentally demonstrate an all-normal-dispersion Yb-doped mode-locked fibre laser with no intentional spectral filter inserted. Pulses with 1.1 nJ pulse energy at a repetition rate of 20.4 MHz are achieved. A theoretical model of the fibre laser is derived, whose coefficients are explicitly dependent on the orientations of the wave plates and the polarizer. Based on the model, stability diagrams of both the mode-locking and the continuous wave regimes of the laser are presented. The influence of group-velocity dispersion （GVD） and cavity length on the stability of mode-locking is also discussed.

关键词： fibre laser mode-locking ytterbium