远红外自由电子激光器脉冲结构

 采用整体数值模拟方法，研究了中物院远红外自由电子激光装置的起振和脉冲结构。给出了为克服激光呆滞效应起振所需的腔长失谐值，腔长调节精度和调节范围。预计了装置的增益、功率、脉冲宽度和谱线宽度等重要参量。研究了不同腔长失谐值下光脉冲结构的变化。     

Recent Progress of the Beijing FEL──Realized Saturated Oscillation

Beijing FEL facility has been built in IHEP,the saturated oscillation has been obtained at a wavelength of 10.68μm,on Dec.28,1993.The average output energy and the pulse width were measured respectively to be 3mJ,2μs.The corresponding osillation power is greater than 210kW,peak power is about 20MW, which is about 10⁸ times higher than that of spontaneous emission. The FWHM of the FEL spectracal bandwidth is less than 2%.The small signal net gain is 24% per pass.The extraction efficiency is 0.45%.In the present experimental resules,BFEL can be saturated by changing electron energy at the wavelength range from 9-10μm,the maxmium average output energy and extraction efficiency are 10mJ,0.52% respectively,the minimum spectral bandwidth of 0.3% has achieved by shorting cavity length.     

加速器噪声对远红外FEL振荡器影响的模拟研究

采用FEL一维脉冲模型,针对中国原子能研究院的远红外FEL振荡器,模拟研究了加速器噪声对FEL的影响。对电子束微脉冲的时间晃动和能量波动所引起的光功率波动及光谱中心晃动进行了模拟计算,在计算中还分别考虑了噪声频率、振幅的大小产生的直接影响以及腔失谐的间接影响。     

加速器噪声对远红外FEL振荡器影响的模拟研究

 采用FEL一维脉冲模型，针对中国原子能研究院的远红外FEL振荡器，模拟研究了加速器噪声对FEL的影响。对电子束微脉冲的时间晃动和能量波动所引起的光功率波动及光谱中心晃动进行了模拟计算，在计算中还分别考虑了噪声频率、振幅的大小产生的直接影响以及腔失谐的间接影响。     

远红外自由电子激光器脉冲结构

采用整体数值模拟方法,研究了中物院远红外自由电子激光装置的起振和脉冲结构。给出了为克服激光呆滞效应起振所需的腔长失谐值,腔长调节精度和调节范围。预计了装置的增益、功率、脉冲宽度和谱线宽度等重要参量。研究了不同腔长失谐值下光脉冲结构的变化。     

Sustained saturation in a free-electron laser oscillator at perfect synchronism of an optical cavity.

The first observation of sustained saturation in a free-electron laser (FEL) oscillator at perfect synchronism of an optical cavity is presented. A simultaneous measurement of FEL power and absolute detuning length of the optical cavity ( deltaL) has clearly shown that the FEL efficiency becomes maximum at deltaL = 0.0+/-1 microm, although it has been considered that only a transient state exists at deltaL = 0 due to the well-known laser lethargy effect. The observed efficiency detuning curve is well reproduced by our numerical simulation including a small shot-noise effect.     

Low-threshold, 12-MHz, multipass-cavity femtosecond Cr4+: Forsterite laser

We report on the development of an extended-cavity, low-threshold femtosecond Cr⁴⁺:forsterite laser operating near 1270 nm. The resonator was end-pumped by a continuous-wave Yb-fiber laser at 1060 nm. The 195-MHz short cavity could be operated with absorbed threshold pump powers as low as about 300 mW. To scale up the pulse energy, the cavity length was increased by using a q-preserving multipass cavity (MPC) consisting of a flat and a curved (R = 4 m), notched high-reflector. Kerr-lens mode locking was used to generate femtosecond pulses and double-chirped mirrors were included in the cavity for dispersion compensation. With an absorbed pump power of 1250 mW, the mode-locked laser produced 4 nJ of pulse energy at an average output power of only 47 mW. The corresponding repetition rate of the extended cavity was 11.7 MHz. The pulse-width was 90 fs and the spectral bandwidth was 23 nm, corresponding to a time-bandwidth product of 0.37.     

980-nm all-fiber mode-locked Yb-doped phosphate fiber oscillator based on semiconductor saturable absorber mirror and its amplifier

A 980-nm semiconductor saturable absorber mirror(SESAM) mode-locked Yb-doped phosphate fiber laser is demonstrated by using an all-fiber linear cavity configuration. Two different kinds of cavity lengths are introduced into the oscillator to obtain a robust and stable mode-locked seed source. When the cavity length is chosen to be 6 m, the oscillator generates an average output power of 3.5 m W and a pulse width of 76.27 ps with a repetition rate of 17.08 MHz. As the cavity length is optimized to short, 4.4-m W maximum output power and 61.15-ps pulse width are produced at a repetition rate of 20.96 MHz. The output spectrum is centered at 980 nm with a narrow spectral bandwidth of 0.13 nm. In the experiment, no undesired amplified spontaneous emission(ASE) nor harmful oscillation around 1030 nm is observed. Moreover,through a two-stage all-fiber-integrated amplifier, an output power of 740 m W is generated with a pulse width of 200 ps.     

Influences of cavity dispersion distribution on the output pulse properties of an all-normal-dispersion fiber laser

In this paper, the influences of the dispersion distribution in the cavity on the output pulse properties of the all-normaldispersion(ANDi) fiber laser are investigated. Our simulations show that, as the relative length of the dispersion fiber increases, the temporal width and the spectral bandwidth of the output pulse for an ANDi fiber laser with fixed total cavity dispersion or fiber length are decreased, while the pulse energy is enhanced and the compressed pulse width is increased.These simulation predictions have been proved by our experimental results. The reason may be that the nonlinear phase shift accumulated in the nonlinear fiber is more than that in the dispersion fiber if they have the same length.     

Dye laser pumped, continuous-wave KTP optical parametric oscillators

4 (KTP) optical parametric oscillators (OPOs) with pump and idler resonant cavities. With a linear two-mirror cavity the pump power at threshold was 70 mW. The single-frequency signal and idler output wavelengths were tuned in the range of 1025 to 1040 nm and 1250 to 1380 nm by tuning the dye laser in the range of 565 to 588 nm. With a dual three-mirror cavity the threshold was 135 mW. Pumped by 500 mW of 578 nm radiation the 1040 nm single-frequency signal wave output power was 84 mW. Power and frequency stable operation with a spectral bandwidth of less than 9 MHz was obtained by piezo-electrically locking the length of the pump resonant cavity to the dye laser wavelength. Similar performance was achieved by placing the idler resonant OPO inside the resonator of the dye laser. With this system power stable and single-frequency operation was achieved with a spectral bandwidth of less than 11 MHz for the idler wave. Received: 3 February 1998/Revised version: 9 March 1998     

Picosecond and subpicosecon pulse generation in synchronously pumped mode-locked cw dye lasers

Generation of tunable near-infrared picosecond and subpicosecond pulses in a synchronously pumped cw mode-locked Oxazine-1-perchlorate dye laser has been investigated for different values of the important system parameters. The experimental results confirm the predictions of a simple theoretical model which describes the steady-state pulse duration in terms of gain modulation strength, pump power, intracavity bandwidth, pump pulse length and cavity detuning. For a pump-pulse length of 100 ps and a bandwidth of more than 500 Å for the intracavity tuning element dye-laser pulses as short as 0.35 ps have been obtained. Under these conditions up to 100 mW of average output power were provided. In addition, mode-locking of an Oxazine 750 dye laser by synchronous pumping with the cw train of pulses obtained from the Oxazine-1-Perchlorate laser is reported.     

自由电子激光放大啁啾脉冲的数值模拟

利用1维非定态程序对单程自由电子激光(FEL)放大器放大线性啁啾脉冲的过程进行了数值模拟,得到了不同啁啾参数的脉冲通过FEL放大器的增益曲线,计算了不同啁啾参数的脉冲被单程FEL放大器放大后的腔外压缩情况。通过对数值模拟结果的定性分析得出：影响输出脉冲宽度和峰值功率的主要因素是FEL放大器的增益线宽和啁啾参数,并以此说明,通过先使用FEL放大器放大啁啾脉冲、然后再将其在腔外压缩的方法产生超短脉冲FEL是可行的。     

自由电子激光放大啁啾脉冲的数值模拟

 利用1维非定态程序对单程自由电子激光(FEL)放大器放大线性啁啾脉冲的过程进行了数值模拟,得到了不同啁啾参数的脉冲通过FEL放大器的增益曲线,计算了不同啁啾参数的脉冲被单程FEL放大器放大后的腔外压缩情况。通过对数值模拟结果的定性分析得出：影响输出脉冲宽度和峰值功率的主要因素是FEL放大器的增益线宽和啁啾参数,并以此说明,通过先使用FEL放大器放大啁啾脉冲、然后再将其在腔外压缩的方法产生超短脉冲FEL是可行的。     

高能量环形长腔再生放大啁啾脉冲激光的研究

介绍了一种新型的高能量环形长腔再生放大器, 通过对谐振腔的模式分布进行计算, 建立了腔长为12 m的环形腔再生放大器, 在150 mJ的抽运能量下, 得到了单脉冲能量为20 mJ的放大激光输出, 对应的转化效率为13.3%, 其输出激光的能量远远超过了常规的再生放大器输出激光的单脉冲量. 放大激光的输出光谱为30 nm, 可以支持<40 fs的傅里叶转换极限脉宽. 关键词： 环形腔 再生放大 高能量     

滤波对8字腔掺铒光纤激光器锁模运转的影响

构建了基于损耗非对称非线性光学环镜的8字腔掺铒光纤锁模激光器,并讨论了腔内滤波带宽对腔内脉冲演化和激光器输出特性的影响.在非线性光学环镜中引入双向输出耦合器,耦合器和传输光纤位置的不对称产生非互易性,实现锁模运转.利用自制的可调谐滤波器实验研究了滤波带宽对激光器的影响.当滤波带宽为2.1 nm时,腔内脉冲的演化过程受滤波和孤子效应的共同作用,激光器顺时针和逆时针输出脉冲半高全宽分别为583.7fs和2.94 ps.随着滤波带宽增大,滤波的作用逐渐减弱,激光器两路输出脉冲参数逐渐接近,并接近傅里叶变换极限脉冲.当滤波带宽较大时,腔内脉冲的演化过程受增益谱和孤子效应的共同作用,激光器顺时针和逆时针输出脉冲均为变换极限脉冲,半高全宽约为440 fs.通过调节滤波器中心波长实现了对激光器输出脉冲光谱的连续调谐,调节范围大于30 nm.     

Continuously tunable, high-power, single-mode radiation from a short-pulse free-electron laser

This paper gives the first demonstration of high-power, continuously tunable, narrowband radiation that is produced by means of a free-electron laser (FEL) in the far-infrared region of the electromagnetic spectrum. A Fox-Smith intracavity étalon was used to induce phase coherence between the 40 optical micropulses that were circulating in the laser cavity. The corresponding phase-locked spectrum consisted of a comb of discrete frequencies separated by 1 GHz. A pair of external Fabry-Pérot étalons was used to filter out a single line from this spectrum. The power in the selected narrow line at 69 microm wavelength was equal to 250 mW during the macropulse of the laser. The spectral width of the selected line is as small as that of a single cavity mode, i.e., a fraction of 25 MHz, in single macropulses of the laser. The average bandwidth of 25 MHz is determined by mode hopping of the phase-locked FEL. The selected frequency hops over 25 MHz between the extrema of this band. The influence of partially coherent spontaneous emission and mode hopping on the final linewidth was studied. The narrow-linewidth radiation was scanned in frequency over 1 GHz. We show that the possibilities to scan over smaller or larger frequency intervals are unlimited.     

高温高压制备Cr2+: ZnSe单晶及其光学性质

为了得到高质量、大尺寸Cr²⁺: ZnSe中红外激光晶体,以适应高功率全固态中红外激光器的发展要求,在高温高压下全石墨腔内运用布里奇曼晶体生长方法,生长出了高质量Ф 30×120 mm Cr²⁺: ZnSe单晶。采用X射线粉末衍射(XRD)、透射电镜(TEM)、红外稳态吸收及荧光光谱等测试方法对晶体的结构及光谱特性进行了表征,并探讨了Cr²⁺: ZnSe晶体中Cr²⁺的能级结构及跃迁机理。结果表明:所生长的Cr²⁺: ZnSe单晶结构均匀,性质稳定,1.97 μm激发的荧光光谱覆盖1.9~3 μm范围,可用于获得2~3 μm全固态中红外激光。     

基于MgO:APLN的1.57μm/3.84μm连续波内腔多光参量振荡器研究

报道了一种基于MgO:APLN实现1.57 μm和3.84 μm跨周期参量光连续输出的内腔抽运多光参量振荡器. 采用1064 nm谐振腔与多光参量振荡腔折叠型复合结构, 综合考虑高功率抽运下谐振腔的热稳定性及多光参量振荡过程的光斑模式匹配, 通过对两个子腔谐振结构的数值模拟分析, 确定了最佳腔型参数. 在此基础上, 进一步研究了谐振参量光透过率对振荡阈值、抽运光下转换效率、输出功率稳定性的影响, 最终实现了3.13 W的1.57 μm和0.85 W的3.84 μm参量光输出, 对应斜效率为6.8%和1.9%, 输出功率稳定性分别达到了1.8%和3%.     

光梳主动滤波放大实现锶原子光钟二级冷却光源

提出一种结合注入锁定技术的主动滤波放大方法,将光梳直接注入锁定至光栅外腔半导体激光器,产生窄线宽激光光源,该光源可以用于锶原子光钟二级冷却.实验中,将中心波长为689 nm,带宽为10 nm的光梳种子光源注入689 nm光栅式外腔半导体激光器,通过半导体增益光谱与半导体光栅外腔,从飞秒光梳的多个纵模梳齿中挑选出一个纵模模式来进行增益放大,再通过模式竞争,实现单纵模连续光输出;同时,光梳的重复频率锁定在线宽为赫兹量级的698 nm超稳激光光源上,因此,注入锁定后输出的窄线宽激光也继承了超稳激光光源的光谱特性.利用得到的输出功率为12 mW的689 nm窄线宽激光光源实现了88Sr原子光钟的二级冷却过程,最终获得温度为3μK,原子数约为5×10~6的冷原子团.该方法可拓展至原子光钟其他光源的获得,从而实现原子光钟的集成化和小型化.