Group delay dispersion compensation in an Ytterbium-doped fiber laser using intracavity Gires-Tournois interferometers

This paper reports the use of a pair of multi-cavity Gires-Tournois interferometer (GTI) mirrors in a ring cavity Ytterbium-doped fiber laser for dispersion compensation. The optical spectrum was broadened by 6 nm due to the large negative group delay dispersion introduced by the light undergoing 10 round trips between the GTI mirrors. The design of the GTI mirrors and the optimisation of the layers are discussed and fabrication results are presented.     

Back-side-coated chirped mirrors with ultra-smooth broadband dispersion characteristics

We demonstrate a new technique for the design of chirped mirrors with extremely smooth dispersion characteristics over an extended ultra-broadband wavelength range. Our approach suppresses spectral dispersion oscillations, which can lead to unwanted strong spectral modulations and limit the bandwidth of mode-locked laser pulses. Dispersion oscillations are significantly reduced by coating the chirped mirror structure on the back side of a substrate, providing ideal impedance matching between coating and ambient medium. An anti-reflection coating may be added on the front side of the substrate, geometrically separated from the chirped mirror. The chirped mirror structure and the anti-reflection coating are non-interfering and can be independently designed and optimized. The separation of both coating sections provides a much better solution for the impedance-matching problems than previous approaches to chirped mirror design. We show by a theoretical analysis and numerical simulations that minimum dispersion oscillations are achieved if the index of the substrate is identical to the index of one of the coating materials and if double-chirping is used for the chirped mirror structure. Based on this analysis, we design a mirror that supports a bandwidth of 220 THz with group delay dispersion oscillations of about 2 fs² (rms), an order-of magnitude improvement compared to previous designs of similar bandwidth. In a first experimental demonstration of back-side-coated (BASIC) mirrors, we achieve nearly transform-limited and virtually unchirped pulses of 5.8 fs duration from a Kerr-lens mode-locked Ti:sapphire laser. BASIC mirrors are particularly suited for higher-order dispersion compensation schemes. They support the extremely broad spectra of few-cycle pulses and promise to provide clean pulse shapes in this regime. Received: 19 April 2000 / Published online: 6 September 2000     

Integrative optimization of chirped mirrors for intracavity dispersion compensation

A new integrative optimization of three chirped mirrors for precise broadband intracavity group delay dispersion compensation in ring cavity is proposed. Simulation demonstrates that the residual group delay dispersion ripples of these three chirped mirrors are less than 25 fs² for most of the wavelengths from 600 to 1200 nm. Pulse evolution simulation shows that these three matched chirped mirrors compensate the group delay dispersion in the Ti:Sapphire ring cavity laser well to obtain an octave-spanning spectrum.     

Double Gires-Tournois interferometer negative-dispersion mirrors for use in tunable mode-locked lasers

We report the implementation and operation of novel superhigh-reflectivity negative-dispersion dielectric mirrors for use in tunable ultrafast laser systems. The mirror structure is divided into two distinct regions: an underlying superhigh-reflectivity dielectric quarter-wavelength stack and an overlying negative-dispersion section consisting of only a few layers and forming simple multiple Gires-Tournois interferometers. The example that we present was designed for operation from 800 to 900 nm and has a near-constant group-delay dispersion of -40 fs(2) and a peak reflectivity greater than 99.99%. We show a comparison of the predicted and the measured mirror performance and application of these mirrors in a mode-locked Ti:sapphire laser tunable from 805 to 915 nm.     

Mirror-dispersion-controlled OPA: a compact tool for sub-10-fs spectroscopy in the visible

We report on a sub-10-fs optical parametric amplifier in the visible, using noncollinear phase matching in #-barium borate, with a pulse compressor made exclusively of chirped dielectric mirrors. We employ mirrors of novel design, providing negative group delay dispersion for bandwidths of over 200 THz, up to the blue-green spectral region. The resulting setup, compact, easy to operate and reliable, is an ideal tool for ultrafast spectroscopy with extremely high time resolution. We use these pulses to observe in the time domain coherent oscillations in organic molecules with period as short as 16 fs.     

Cr∶LiSAF飞秒激光器中Gires-Tournois镜的设计

飞秒激光脉冲的产生主要依赖于激光腔内净的负群延迟色散.但是在固体激光器中,增益介质和其它光学元件却引入了正色散,因此需引入相应的色散补偿机制.布儒斯特角棱镜对曾是激光腔中色散补偿的主要办法,但是它在进行群延迟色散补偿的同时还会引入高阶色散,使激光器操作困难并影响激光器的尺寸和重复频率.Gires-Tournois镜是一种新型的色散补偿元件,可以克服这些缺点.本文介绍了Gires-Tournois镜的基本结构,分析了影响Gires-Tournois镜的群延迟时间、群延迟色散和三阶色散的量,给出了Gires-Tournois镜的设计原则并根据Cr∶LiSAF飞秒激光器中的色散补偿要求设计了性能优良的Gires-Tournois镜.该Gires-Tournois镜在750~900 nm的波长范围内具有高于99.9%的反射率和-35±8fs2的群延迟色散.用这样的Gires-Tournois镜经过4次反射后可以补偿3mm的Cr∶LiSAF晶体的绝大部分群延迟色散.     

Theoretical investigation of chirped mirrors in semiconductor lasers

This paper reports a theoretical design of chirped mirrors in 1.3-μm double-section semiconductor lasers to achieve high reflectivity and dispersion compensation over a broad bandwidth. Analytic expressions for reflectivity, group delay and group delay dispersion are derived. We use for the first time chirped air/semiconductor layer pairs as mirrors for higher-order dispersion compensation in semiconductor lasers. Our optimised calculations demonstrate that the broad-band mirrors designed consist of a total of only 12 air/semiconductor layers and achieve a reflectivity higher than 99.8%, a smooth group delay and almost stable dispersion in the laser cavity over a 100-nm bandwidth. Due to a high index contrast of both types of the layers, n _l = 1, n _h~ 3.5, a high-reflectivity bandwidth of > 700 nm is obtained in 1.3-μm semiconductor lasers. We also compare our results with that of a commercial simulation program and show a good agreement between them. As a conclusion, we assume from the theoretical results that air/semiconductor layer pairs with varying thicknesses used at one end of double-section semiconductor lasers can lead to femtosecond optical pulse generation using mode-locking techniques. An erratum to this article can be found at .     

Brewster-angled chirped mirrors for broadband pulse compression without dispersion oscillations

We use Brewster-angled chirped mirrors for dispersion compensation of a noncollinear optical parametric amplifier. This novel mirror design virtually eliminates spurious surface reflections and resultant dispersion ripple. The absence of compression artifacts is demonstrated by the generation of clean 5.6 fs pulses, with what is believed to be an unprecedented low ripple-induced satellite content for a nonadaptive scheme. In addition, the 270 THz spectral coverage allows generation of widely tunable visible pulses of 8 to 15 fs duration.     

飞秒激光脉冲压缩用啁啾镜新设计方法

对配对啁啾镜传统的优化过程进行了改进,并且尝试了新的多个啁啾镜匹配的方法。理论上实现了在700～1050 nm光谱范围内,两个啁啾镜配对色散总和振荡小于±10 fs2,三个啁啾镜配对色散总和振荡小于±15 fs2。此配对啁啾镜所实现的精确补偿色散,是获得极短光脉冲的基础,可以用于飞秒激光的脉冲压缩。     

钛宝石激光器9.5 fs脉冲输出中的啁啾镜色散补偿

根据钛宝石激光器的要求,实验设计了中心波长800 nm带宽200 nm的啁啾镜,在700—900 nm波长范围内提供约-60 fs²群延迟色散(group delay dispersion,GDD).采用双射频离子束溅射方法进行制备,用实验室搭建的白光干涉仪进行色散性能测试,从测试结果可以看出,制备的啁啾镜的性能和设计值符合得比较好.制备得到的非成对啁啾镜在钛宝石激光谐振腔中进行色散补偿,锁模后分别获得了12 fs和9.5 fs的激光脉冲输出.这是目前报道的使用国产啁啾镜获得的最短的 关键词： 啁啾镜 群延迟色散 色散补偿 钛宝石激光器     

Mirror-dispersion-controlled sub-10-fs optical parametric amplifier in the visible

Pulses from an optical parametric amplifier in the visible are compressed to sub-10-fs duration by a delay line made exclusively from chirped dielectric mirrors. We employ what we believe are the first ultrabroadband visible chirped mirrors, which provide negative group-delay dispersion up to the blue-green spectral region. The setup is compact and reliable, and we used it to observe, for what is to our knowledge the first time in organic molecules, coherent oscillations with periods as short as 16 fs.     

Shape selection of wavelets for accurate chromatic dispersion measurement of white-light spectral interferograms

The group delay of chirped mirrors can be directly read from the ridge of wavelet-transform of white-light spectral interferograms. In this paper, we investigate the influence of Gabor wavelet shaping factor on the precision of the group-delay dispersion extraction. The rule of selection of shaping factor is given for accurate chromatic dispersion measurement of chirped mirrors.     

Dispersionless saturable absorber mirrors with large modulation depths and low saturation fluences

We show that it is possible to eliminate group delay dispersion over wide bandwidths in low-finesse, resonant saturable absorber mirrors, whilst maintaining a low saturation fluence and a high modulation depth. By modelling the mirror structure we demonstrate that these properties can be produced by capping a resonant device with a single dielectric layer of carefully selected refractive index. We show that a specially capped dispersionless structure minimises the temporal broadening of femtosecond pulses reflected from the mirror. We compare this device against uncapped-resonant and anti-resonant structures. The superior performance of the capped, dispersionless device was verified experimentally by comparing resonant, anti-resonant and dispersionless quantum-dot (QD) saturable absorber mirrors incorporated into a Cr⁴⁺:forsterite laser system. We found that a minimum pulse duration of 86 fs could be achieved for the dispersionless structure at 1290 nm with an output power of 55 mW compared to 122 fs in an anti-resonant structure and several-picosecond pulses for a resonant structure.     

Relationships among group delay,energy storage,and loss in dispersive dielectric mirrors

We show that absorbed and stored electromagnetic energy are proportional to the reflection group delay in highly reflective dispersive dielectric mirrors over the high-reflectivity band.Our theoretical considerations are verified by numerical simulations performed on different dielectric mirror structures.The revealed proportionality between group delay and absorbed energy sets constraint on the application of ultrabroadband and/or dispersive dielectric mirrors in broadband or widely tunable,high-power laser systems.     

基于白光干涉测量色散补偿薄膜的群延迟色散

为精确测量超快激光色散补偿薄膜的群延迟色散,提出了一种基于窗口傅里叶变换和样条插值去噪算法的新型白光干涉测量方案。计算机模拟表明此方法测试精度可达0.58fs2。分析了高斯噪声和光强平均效应对测试精度的影响,并使用此方法对实验制备的Gires-Tournois干涉反射镜和啁啾镜进行了测试,在宽光谱范围内测试误差小于10fs2。该方法相比其他算法可以更快速、更精确地实现薄膜相位信息的提取,具有更高的测试精度和实用性。     

太赫兹量子级联激光器频率梳的色散

群速度色散会限制太赫兹量子级联激光器频率梳的稳定以及频谱宽度.对于太赫兹量子级联激光器频率梳,其色散主要由器件增益、波导损耗、材料损耗引起.研究基于4.2 THz量子级联激光器双面金属波导结构,通过建立德鲁德模型,利用有限元法计算了激光器的波导损耗;器件未钳制的增益由费米黄金定则计算得到,结合增益钳制效应,计算了器件子带电子跃迁吸收以及镜面损耗,得到了器件钳制后的增益;利用Kramers-Kronig关系得到了器件的增益、波导损耗、材料损耗引起的色散,结果表明器件的激射区域存在非常严重的色散(–8×10~5—8×10~5 fs~2/mm).同时,计算了一种基于Gires-Tournois干涉仪结构的色散,结果表明,该结构的色散具有周期性,可以用于太赫兹量子级联激光器的色散补偿.     

太赫兹自由电子激光光腔光子晶体镜的设计

利用传输矩阵法对太赫兹自由电子激光光腔光子晶体镜进行了模拟设计,中心波段在1~3 THz。对光腔镜的光子晶体结构参数如介质厚度、层数、折射率与反射率的关系等进行了研究,并给出了一维光子晶体用于高反镜的设计方法。通过对耦合输出镜光子晶体中引入缺陷层情况的数值模拟,发现通过对缺陷层的调节设计,可以实现耦合输出率的可调谐;并给出了可用于THz 自由电子激光光腔耦合输出镜的调节方法。通过对介质层厚度的调节设计,可以实现反射光谱的整体移动,从而实现宽谱可调谐,扩大了高反镜及耦合输出镜的调节范围。     

1.5-octave chirped mirror for pulse compression down to sub-3 fs

We demonstrate numerically and experimentally a chirped mirror with controlled reflectivity and dispersion of up to 1.5 octaves. A complementary pair of such mirrors has a reflectivity of 95% in the wavelength range 400–1200 nm with residual group delay dispersion ripples <100 fs² in all of this range. The mirror pair allows one to compensate a chirp of the corresponding spectrum (with a smooth phase), resulting in sub-3-fs pulses. PACS 42.65.Re; 42.79.Fm; 42.79.Wc     

全啁啾镜色散补偿的亚8 fs钛宝石激光器

报道了一种基于全啁啾镜腔内色散补偿的、可长期稳定运行的亚8 fs钛宝石激光器.在4 W绿光抽运下, 可获得300 mW、86 MHz脉冲输出.腔内用于色散补偿的两对啁啾镜是国内自主设计自行镀膜的, 其对色散的精确控制可以在腔内不加尖劈对的情况下获得半宽超过150 nm超宽带输出.利用腔外色散补偿, 脉冲宽度被压缩至7.9 fs, 这是目前采用国产啁啾镜获得的最短脉宽, 也是无尖劈对谐振腔获得的最短脉宽.同时, 利用电路系统提供实时反馈调节, 可保证钛宝石激光器长期稳定运行, 24 h内功率抖动约0.6%.     

钛宝石激光器中用优化Gires-Tournois镜产生15 fs脉冲

根据飞秒脉冲锁模钛宝石激光器脉冲压缩的要求,介绍了负色散镜补偿色散的基本原理及其特点。详细阐述了优化Gires-Tournois(OG-T)镜的设计过程,并通过计算机优化得到理想设计膜系。采用离子束溅射的方法镀制了优化Gires—Tournois镜。测量了优化Gires-Tournois镜(编号为OGT#1)的透射率和群延迟色散,并与设计值进行了比较,分析了实测值产生偏差的原因,从而对镀膜参量进行了相应的调整,制造了第二批优化Gires—Tournois镜(编号为OGT#2)。将优化Gires—Tournois镜用于钛宝石激光器振荡级内,单程5次通过三个优化Gires-Tournois镜,补偿了激光器腔内色散,实现了飞秒锁模脉冲运转。用OGT#1先进行了实验,获得32fs的脉冲和46nin的光谱宽度。用调整参量后的OGT#2进行了实验,获得了15fs的超短脉冲和91nm的光谱宽度。实验很好的验证了负色散镜补偿色散的优点,为国内啁啾镜的研制创造了条件。