Enbang Li

Continuous-wave, 15.2 W diode-end-pumped Nd:YAG laser operating at 946 nm

A high-power continuous-wave (cw) Nd:YAG laser operating at 946 nm by utilizing a quasi-three-level transition is reported. The laser consists of a composite Nd:YAG rod end pumped by a fiber-coupled diode laser and a simple plane-concave cavity. At an incident pump power of 40.2 W, a maximum cw output of 15.2 W at 946 nm is obtained, achieving a slope efficiency of 45%. To the best of our knowledge, this is the highest output at 946 nm ever generated by diode-pumped Nd:YAG lasers. In addition, at an incident pump power of 15.2 W, a 1.25 W blue output at 473 nm is achieved with a simple compact three-element cavity and a type-I lithium triborate (LiB(3)O(5)) crystal as a frequency doubler.

Octave spanning supercontinuum in an As 2 S 3 taper using ultra-low pump pulse energy

An octave spanning spectrum is generated in an As2S3 taper via 77 pJ pulses from an ultrafast fiber laser. Chirp compensation allows the octave to be generated directly from the un-amplified laser output.

Photonic chip based tunable and reconfigurable narrowband microwave photonic filter using stimulated Brillouin scattering

We report the first demonstration of a photonic chip based dynamically reconfigurable, widely tunable, narrow pass-band, high Q microwave photonic filter (MPF). We exploit stimulated Brillouin scattering (SBS) in a 6.5 cm long chalcogenide (As2S3) photonic chip to demonstrate a MPF that exhibited a high quality factor of ~520 and narrow bandwidth and was dynamically reconfigurable and widely tunable. It maintained a stable 3 dB bandwidth of 23 ± 2MHz and amplitude of 20 ± 2 dB over a large frequency tuning range of 2-12 GHz. By tailoring the pump spectrum, we reconfigured the 3 dB bandwidth of the MPF from ~20 MHz to ~40 MHz and tuned the shape factor from 3.5 to 2 resulting in a nearly flat-topped filter profile. This demonstration represents a significant advance in integrated microwave photonics with potential applications in on-chip microwave signal processing for RADAR and analogue communications.

High-energy, kHz-repetition-rate, ps cryogenic Yb:YAG chirped-pulse amplifier

We demonstrate amplification of picosecond laser pulses to 40?mJ at a 2?kHz pulse repetition frequency (PRF) from a two-stage cryogenic chirped-pulse Yb:YAG amplifier, composed of a regenerative amplifier (RGA) and a two-pass booster amplifier. The RGA produces 8.2mJ of energy at 2kHz PRF and 13.2mJ at 1kHz PRF with excellent energy stability (approximately 0.3% rms) and beam quality (M(2)<1.1). Pulse stretching and compression are achieved by using a chirped fiber Bragg grating and a multilayer dielectric grating pair, respectively. Compressed 15?ps pulses from the RGA are obtained with a throughput efficiency of approximately 80% (approximately 6.5 mJ for 2kHz). The booster amplifier further amplifies the pulses to 40mJ at 2kHz PRF, and approximately 32 mJ, approximately 15 ps pulses are expected after compression. The amplifier chain seeded from a femtosecond Yb-fiber laser enables the optical self-synchronization between signal and pump in optical parametric chirped-pulse amplifier applications.

Temperature compensation of multimode-interference-based fiber devices.

Single-mode-multimode-single-mode (SMS) fiber structures have been demonstrated to be a simple and effective way to realize multimode interference (MMI) in optical fibers. The temperature dependence of the spectral characteristics of SMS devices is investigated. By utilizing the feature that the response spectra of SMS devices with opposite polarities to temperature and axial tensile strain, I demonstrate that temperature compensation of SMS devices can be realized by using materials with a proper coefficient of thermal expansion. A temperature stability of 1.0 pm/ degrees C has been experimentally demonstrated with a ceramic as the packaging material.

Multi-frequency and multiple phase-shift sinusoidal fringe projection for 3D profilometry

In this paper, we report on a laser fringe projection set-up, which can generate fringe patterns with multiple frequencies and phase shifts. Stationary fringe patterns with sinusoidal intensity distributions are produced by the interference of two laser beams, which are frequency modulated by a pair of acousto-optic modulators (AOMs). The AOMs are driven by two RF signals with the same frequency but a phase delay between them. By changing the RF frequency and the phase delay, the fringe spatial frequency and phase shift can be electronically controlled, which allows high-speed switching from one frequency or phase to another thus makes a dynamic 3D profiling possible.

Photonic Aharonov–Bohm effect in photon–phonon interactions

The Aharonov–Bohm effect is one of the most intriguing phenomena in both classical and quantum physics, and associates with a number of important and fundamental issues in quantum mechanics. The Aharonov–Bohm effects of charged particles have been experimentally demonstrated and found applications in various fields. Recently, attention has also focused on the Aharonov–Bohm effect for neutral particles, such as photons. Here we propose to utilize the photon–phonon interactions to demonstrate that photonic Aharonov–Bohm effects do exist for photons. By introducing nonreciprocal phases for photons, we observe experimentally a gauge potential for photons in the visible range based on the photon–phonon interactions in acousto-optic crystals, and demonstrate the photonic Aharonov–Bohm effect. The results presented here point to new possibilities to control and manipulate photons by designing an effective gauge potential.

Three-dimensional profilometry based on shift estimation of projected fringe patterns

This paper presents a new approach to fringe pattern profilometry. In this paper, a generalized model describing the relationship between the projected fringe pattern and the deformed fringe pattern is derived, in which the projected fringe pattern can be arbitrary rather than being limited to being sinusoidal, as are those for the conventional approaches. Based on this model, what is believed to be a new approach is proposed to reconstruct the three-dimensional object surface by estimating the shift between the projected and deformed fringe patterns. Additionally, theoretical analysis, computer simulation, and experimental results are presented, which show how the proposed approach can significantly improve the measurement accuracy, especially when the fringe patterns are distorted by unknown factors.

8.3 W diode-end-pumped continuous-wave Nd:YAG laser operating at 946-nm

This paper reports a diode-end-pumped continuous-wave (CW) Nd:YAG laser operating at 946-nm by utilizing the 4F3/2-4I9/2 transition. We demonstrated that at an incident pump power of 27.7 W, an output power of 8.3-W could be achieved with a slope efficiency of 33.5%. To the best of our knowledge, this is the highest CW output power at 946 nm generated by LD end-pumped Nd:YAG lasers. By using intracavity frequency doubling with an LBO crystal, we further obtained a 473-nm blue laser with an output power of 1.2 W, achieving an optical-to-optical conversion efficiency of 7.1% at a pump power of 16.9 W. The short-term power instability of the blue laser was less than 1 %.

Measurements in microscopic flow with a solid-state LDA

The application of a solid-state laser doppler anemometer (LDA) to laminar flow occurring in a 175 μm channel is reported. Details of the optical system are described.