Pulse picking by phase-coherent additive pulse generation in an external cavity

We have implemented a simple method for generating an "amplified" phase-coherent light pulse in which a pulse train of phase-coherent, equidistant input light pulses from a mode-locked Ti:sapphire laser is coupled into a ring cavity resonator whose length is matched to the mode-locked pulse repetition frequency at 82 MHz. Pulses are thus coherently superimposed and added inside the buildup cavity and form an intense pulse that is switched out from the cavity via a fast acousto-optic modulator. The method thus provides a pulse train at a reduced and controlled repetition frequency and with higher pulse energies than the original mode-locked pulses.     

基于色散不对称光纤环形镜的锁模光纤激光器

在理论上数值计算了各种常量对色散不对称非线性光纤环形镜透射特性的影响。并分析了它作为被动锁模器件用于光纤激光器压窄脉冲的物理机制。利用8字形主被动混合锁模的结构在调制频率为9．998748700 GHz，波长为1566．65nm处获得了11ps的稳定锁模脉冲输出．对应谱宽0．297nm．同时在重复频率为9．995792825 GHz和9．996778256 GHz时分别得到了振幅均匀的二阶和三阶谐波锁模输出。证明色散不对称非线性光纤环形镜可以有效消减脉冲的尾翼和噪声．得到脉幅稳定的脉冲序列。     

脉冲幅度均匀化的有理谐波锁模光纤激光器

提出并实现了一种脉冲幅度可均匀化的有理谐波锁模光纤激光器。该激光器采用主动有理谐波锁模机制,可获得重复频率为整数倍调制频率的锁模脉冲信号。通过在光纤激光器谐振腔中添加非线性光纤放大环镜,并利用其反射率对输入信号强度的开关特性,实现对锁模脉冲信号的整幅。在1 GHz的调制频率下,分别获得了4 GHz和5 GHz重复频率的锁模脉冲信号输出,并且在一定的980 nm抽运功率下,可通过调节电光调制器的直流偏置电压大小以及调制信号的调制深度,使得脉冲幅度具有较好的均匀性。     

Pulse energy modulation of the cw-mode-locked 1.32 μm Nd-YAG-laser by drive frequency detuning

The frequency of an acousto-optic mode-locker is detuned from the fundamental resonance frequency of the cavity resulting in undamped oscillations of the laser pulse energy. The envelope of the mode-locked pulse train consists of spikes 10 μs wide with a repetition time of 46 μs. The energy of the mode-locked pulses in a spike is increased by up to a factor of 50 compared to a cw-mode-locked pulse. The pulse width can be as short as 700 ps.     

Ultralow-jitter passive timing stabilization of a mode-locked Er-doped fiber laser by injection of an optical pulse train

The pulse timing of a mode-locked Er-doped fiber laser was stabilized to a reference pulse train from a Cr:forsterite mode-locked laser by all-optical passive synchronization scheme. The reference pulses were injected into a ring cavity of the fiber laser by using a 1.3-1.5 mum wavelength-division multiplexer. The spectral shift induced by cross-phase modulation between copropagating two-color pulses realizes self-synchronization due to intracavity group-delay dispersion. The rms integration of timing jitter between the fiber laser pulse and the reference pulse was 3.7 fs in a Fourier frequency range from 1 Hz to 100 kHz.     

Diode-laser pumped high-power and actively mode-locked Nd:YLF laser with fast switching

In an actively mode-locked laser, self-phase modulation can make pulse shorter at the expanse of causing instability at high pumping power. Using fast switching on the acousto-optic modulator, we can generate an actively mode-locked pulse train with shorter pulse width and higher average power than that driven by a sinusoidal signal. A 9-ps pulse train was generated in a mode-locked laser with an average power of 600 mW whose power level, to our knowledge, is the highest for diode-pumped and mode-locked Nd:YLF lasers.     

Single pulse extraction from a mode-locked pulse train using a dye-laser amplifier

A new method to generate high power, short light pulses with a moderate iteration frequency is described. The pulse train of the actively mode-locked Kr laser was sent into a dye-laser amplifier pumped by a N₂ laser. The trigger of the N₂ laser was generated by dividing the modulation frequency of the mode-locking into moderately low frequency (≈ 50 Hz). Only one pulse in the input train was largely amplified by one N₂ laser pulse and the intense short pulses were generated with ≈ 50 Hz iteration.     

Generation of chirp-free picosecond pulses

The frequency spectrum of moderately chirped laser pulses depends upon the portion of the beam which is accepted by the spectrometer. Observation of the development of the chirp in a mode-locked pulse train allows to determine the small incipient chirp of early pulses. A product, bandwidth times pulse duration, of 0.47 ± 0.03 is consistently observed for single pulses switched from a passively mode-locked Nd-glass system.     

Subfemtosecond compression of periodic laser pulses

It is shown that a recently proposed technique of molecular modulation can be used to compress mode-locked laser pulses into the subfemtosecond domain. The method relies on driving a molecular oscillation with a periodic pulse train. The coherent molecular motion, in turn, modulates the laser frequency and allows pulse compression by group-velocity dispersion of the same molecular medium.     

对撞锁模染料激光器中锁模脉冲列的耦合效应

论述了在对撞锁模染料激光器中必然存在锁模脉冲列耦合效应,此效应使输出脉冲较宽,且脉宽不稳定。用适当加厚锁模染料层等办法减弱该效应会使脉冲变窄且脉宽稳定。     

光学频率合成器

从光学频率合成器的基本原理出发,分析了飞秒锁模脉冲激光在时域和频域上的分布特征,并分别介绍了输出激光的两个重要参数即重复频率fr和零频fceo的几种控制方法,以及光学频率合成器实现频率连接和转换的过程,最后介绍了光学频率合成器两次国际比对研究与结果.     

高能量,长锁模脉冲序列的Nd：YLF激光器研究

首次利用ＧａＡｓ光电导开关构成的反馈回路，正、负反馈联合作用，动态控制Ｎｄ：ＹＬＦ被动锁模激光器腔内的Ｑ值，得到高能量、长序列的稳态锁模脉冲。稳态单脉冲的脉宽为４ｐｓ，能量为９μＪ，脉冲序列长１６μｓ，能量为２．５ｍＪ。     

Dual-polarization mode-locked Nd:YAG laser

A mode-locked solid-state laser containing a birefringent element is shown to emit synchronously two frequency combs associated to the two polarization eigenstates of the cavity. An analytical model predicts the polarization evolution of the pulse train, which is determined by the adjustable intracavity birefringence. Experiments realized with a Nd:YAG laser passively mode locked by a semiconductor saturable absorber mirror are in perfect agreement with the model. Locking between the two combs arises for particular values of their frequency difference, e.g., half the repetition rate, and the pulse train polarization sequence is then governed by the relative overall phase offset of the two combs.     

Subfemtosecond synchronization of microwave oscillators with mode-locked Er-fiber lasers

We synchronize an 8.06 GHz microwave signal from a voltage-controlled oscillator with an optical pulse train from a 77.5 MHz mode-locked Er-fiber laser using a fiber-based optical-microwave phase detector. The residual phase noise between the optical pulse train and the synchronized microwave signal is -133 dBc/Hz (-154 dBc/Hz) at 1 Hz (5 kHz) offset frequency, which results in 838 as integrated rms timing jitter [1 Hz-1 MHz]. The long-term residual phase drift is 847 as (rms) measured over 2 h, which reaches 4×10(-19) fractional frequency instability at 1800 s averaging time. This method has a potential to provide both subfemtosecond-level short-term phase noise and long-term phase stability in microwave extraction from mode-locked fiber lasers.     

40-gHz, 100-fs stimulated-Brillouin-scattering-free pulse generation by combining a mode-locked laser diode and a dispersion-decreasing fiber

A 40-GHz, 100-fs pulse train was successfully generated by soliton compression of a mode-locked laser diode (MLLD) pulse with a dispersion-decreasing fiber. The MLLD had a longitudinal mode linewidth as broad as 60 MHz, which made it possible to suppress stimulated Brillouin scattering and achieve stable, ultrahigh-speed pulse compression without applying external frequency modulation.     

全光纤主动锁模2 μm掺铥脉冲激光器

报道了全光纤结构主动锁模掺铥脉冲激光器,中心波长为1950 nm。利用电光相位调制器对光纤激光器进行腔内相位调制,获得了重复频率为11.884 MHz的主动锁模脉冲输出,脉宽为816 ps。改变泵浦功率、调制信号的频率和幅度,获得了重复频率为4~18 kHz的弛豫振荡调制稳定脉冲输出。锁模和弛豫振荡调制获得的输出脉冲能量波动低于7%。     

同步泵浦PML飞秒激光研究

采用CW锁模YAG倍频激光器同步泵浦PML飞秒染料激光器,产生了平均脉宽约55fs、功率为15mW的光脉冲。文章在理论和实验上还研究了同步泵浦飞秒激光脉冲产生技术。     

对采用BBO晶体锁模Nd：YAG激光器的实验研究

报道了在Nd:YAG激光器中使用BBO倍频晶体进行锁模运转的研究结果.获得的二次谐波单脉冲宽度为28ps.锁模序列脉冲能量为lnJ.     

Ultrahigh-resolution coherence spectroscopy by means of periodic excitation with picosecond pulses

The feasibility of ultrahigh-resolution coherence spectroscopy with a train of picosecond light pulses from a synchronously pumped mode-locked and cavity-dumped dye laser is demonstrated. Narrow resonances of periodic pulse excitation are observed whenever the pulse repetition rate of the laser of a higher harmonic coincides with the frequency splitting of coherently excited levels. The zero-field hyperfine splitting of the Na-ground state (1771.6 MHz) could be measured in the 2100th order of the excitation rate with a resonance halfwidth of 800 Hz.     

Nanosecond Pulses Generation with Samarium Oxide Film Saturable Absorber

Nanosecond pulse generation is demonstrated in a mode-locked erbium-doped fiber laser(EDFL) utilizing a samarium oxide(Sm_2O_3) film. The Sm_2O_3 film exhibits a modulation depth of 33%, which is suitable for modelocking operation. The passively pulsed EDFL operates stably at 1569.8 nm within a pumping power from 109 to 146 m W. The train of generated output pulses has a pulse width of 356 nm repeated at a fundamental frequency of 0.97 MHz. The average output power of 3.91 m W is obtained at a pump power of 146 m W, corresponding to 4.0 nJ pulse energy. The experimental result indicates that the proposed Sm_2O_3 saturable absorber is viable for the construction of a flexible and reliably stable mode-locked pulsed fiber laser operating in the 1.5 m region.