The joint conference of the European Conference on Nonlinear Optical Spectroscopy (ECONOS) and European CARS Workshop (ECW) covers all theoretical and experimental aspects of nonlinear optical spectroscopy and microscopy. Topics include Coherent anti‐Stokes Raman scattering (CARS) spectroscopy and microscopy, other forms of coherent Raman scattering, other approaches to the detection of nonlinear optical responses in time and frequency domain, and investigations of the physical and chemical processes defining the spectral signatures in different nonlinear media. Also, emerging analytical techniques and their applications in biomedical research, material science, and engineering are discussed. The 18th ECONOS conference and 38th CARS workshop were held in Rouen, France, on 7–10 April 2019, chaired by Frédéric Grisch and Benoit Barviau (CORIA, CNRS UMR 6614, Normandie Université, INSA and University of Rouen) as well as Brigitte Attal‐Trétout (ONERA, The French Aerospace Lab). Altogether, 80 participants shared their research in oral sessions and poster sessions and participated in lively discussions and social activities. After a keynote lecture entitled “Nonlinear optical microscopy in the mid‐infrared” by Eric Potma and a welcome reception in the historic town of Rouen on Sunday afternoon, the regular scientific program began on Monday morning at the CORIA facility. Six invited talks were given during the course of the conference, followed by contributed oral presentations, and a poster session. The main social event constituted a guided tour in the historic center of Rouen and the conference dinner at the historic Halle aux Toiles.

This special section of the Journal of Raman Spectroscopy constitutes a selection of five papers presented at ECONOS/ECW 2019. Due to the broad scope of the conference, the papers cover a broad range of methods and their applications to a variety of systems.

Applications of nonlinear optical spectroscopy traditionally cover all states of matter, which are also reflected in this special issue. Four of the papers are concerned with microscopic techniques. Gagliardi et al.^[1^] studied the infrared portion of the supercontinuum emitted by a popular type of photonic crystal fiber in a basic CARS experiment. The dependence of the SC radiation and the CARS signal of the reference cyclohexane sample on the laser operating conditions was evaluated by means of statistical approaches. The data revealed clear correlations that are believed to be of general nature and offer wide applicability. Lanin et al.^[2^] demonstrate an approach for single‐beam optogenetic multimodal nonlinear‐optical microscopy. For this purpose, they combined third‐harmonic generation and three‐photon‐excited fluorescence. Experiments on brain slices and cell cultures showed the potential of the microscopy technique for a subcellular‐resolution, high‐contrast imaging of HeLa‐line cancer‐cell derivatives, as well as mitochondrial and somatic intracellular structures within deep‐brain neurons and astrocytes. De la Cadena et al.^[3^] introduced a high‐sensitivity broadband‐stimulated Raman scattering setup for micro‐spectroscopy in the low‐wavenumber range (<500 cm⁻¹). The system combines a narrowband Stokes pulse with a broadband pump pulse, and the stimulated Raman loss signal is scanned rapidly using a galvanometric mirror. The setup is demonstrated to be capable of measuring the spectra of several solvents and of obtaining hyperspectral data cubes consisting of microscopic images of polymer beads test samples as well as of the distribution of different biological substances within plant cell walls. Arzumanyan et al.^[4^] applied Raman microspectroscopy for distinction of neutrophils transformed during NETosis and the quantitative determination of the level of their transformation. For this purpose, the neutrophil Raman spectra acquired from the samples of human blood at different levels of transformation were analyzed. They achieved detection of statistically significant differences in the spectral archetypes of the neutrophil Raman spectra at different levels of transformation.

Gas‐phase applications have also been a traditional field covered by ECONOS/ECW. Zhang et al.^[5^] produced Cu dimers in a molecular beam and applied two‐color resonant four‐wave mixing spectroscopy to them. From their experiments, they reported the first observation of an excited 0⁺_g state of dicopper. Such states are not observable by direct one‐photon absorption from the ground state, and therefore the use of nonlinear optical phenomena is a prerequisite for this kind of research.

This ECONOS/ECW special section highlights the continuous progress in the area of nonlinear optical spectroscopy and its applications across the science and engineering disciplines. The enthusiasm and creativity of the scientific community as well as the rapid development of novel and improved experimental equipment will ensure an exciting future of nonlinear spectroscopy research.

欧洲非线性光谱会议（ECONOS）和欧洲CARS研讨会（ECW）的联席会议涵盖了非线性光谱和显微镜的所有理论和实验方面。主题包括相干反斯托克斯拉曼散射（CARS）光谱学和显微技术，其他形式的相干拉曼散射，在时域和频域中检测非线性光学响应的​​其他方法，以及研究物理和化学过程的方法，这些方法定义了不同的非线性介质。此外，还讨论了新兴的分析技术及其在生物医学研究，材料科学和工程中的应用。第18届ECONOS会议和第38届CARS研讨会于2019年4月7日至10日在法国鲁昂举行，由FrédéricGrisch和Benoit Barviau（CORIA，CNRS UMR 6614，诺曼底大学，INSA和鲁昂大学）以及BrigitteAttal-Trétout（法国航空航天实验室ONERA）。共有80名参与者通过口头和海报发布会分享了他们的研究成果，并参加了热烈的讨论和社交活动。在周日下午，埃里克·波特玛（Eric Potma）发表了题为“中红外非线性光学显微镜”的主题演讲，并在历史名镇鲁昂举行了欢迎酒会之后，常规的科学计划于周一早晨在CORIA设施开始。会议期间进行了六次受邀演讲，随后进行了口头演讲和海报发布会。主要的社交活动包括在鲁昂历史中心的带导游的游览以及在历史悠久的哈勒辅助厕所的会议晚宴。INSA和鲁昂大学）以及BrigitteAttal-Trétout（法国航空航天实验室ONERA）。共有80名参与者通过口头和海报发布会分享了他们的研究成果，并参加了热烈的讨论和社交活动。在周日下午由埃里克·波特玛（Eric Potma）做了题为“中红外非线性光学显微镜”的主题演讲并在历史名镇鲁昂举行了欢迎酒会之后，常规的科学计划于周一早晨在CORIA设施开始。会议期间进行了六次受邀演讲，随后进行了口头演讲和海报发布会。主要的社交活动包括在鲁昂历史中心的带导游的游览以及在历史悠久的哈勒辅助厕所的会议晚宴。INSA和鲁昂大学）以及BrigitteAttal-Trétout（法国航空航天实验室ONERA）。共有80名参与者通过口头和海报发布会分享了他们的研究成果，并参加了热烈的讨论和社交活动。在周日下午，埃里克·波特玛（Eric Potma）发表了题为“中红外非线性光学显微镜”的主题演讲，并在历史名镇鲁昂举行了欢迎酒会之后，常规的科学计划于周一早晨在CORIA设施开始。会议期间进行了六次受邀演讲，随后进行了口头演讲和海报发布会。主要社交活动包括在鲁昂历史中心的带导游的参观以及在历史悠久的Halle aux Toiles的会议晚宴。80名参与者通过口头会议和海报会议分享了他们的研究成果，并参加了热烈的讨论和社交活动。在周日下午，埃里克·波特玛（Eric Potma）发表了题为“中红外非线性光学显微镜”的主题演讲，并在历史名镇鲁昂举行了欢迎酒会之后，常规的科学计划于周一早晨在CORIA设施开始。会议期间进行了六次受邀演讲，随后进行了口头演讲和海报发布会。主要社交活动包括在鲁昂历史中心的带导游的参观以及在历史悠久的Halle aux Toiles的会议晚宴。80名参与者通过口头会议和海报会议分享了他们的研究成果，并参加了热烈的讨论和社交活动。在周日下午，埃里克·波特玛（Eric Potma）发表了题为“中红外非线性光学显微镜”的主题演讲，并在历史名镇鲁昂举行了欢迎酒会之后，常规的科学计划于周一早晨在CORIA设施开始。会议期间进行了六次受邀演讲，随后进行了口头演讲和海报发布会。主要的社交活动包括在鲁昂历史中心的带导游的游览以及在历史悠久的哈勒辅助厕所的会议晚宴。在周日下午，埃里克·波特玛（Eric Potma）发表了题为“中红外非线性光学显微镜”的主题演讲，并在历史名镇鲁昂举行了欢迎酒会之后，常规的科学计划于周一早晨在CORIA设施开始。会议期间进行了六次受邀演讲，随后进行了口头演讲和海报发布会。主要的社交活动包括在鲁昂历史中心的带导游的游览以及在历史悠久的哈勒辅助厕所的会议晚宴。在周日下午，埃里克·波特玛（Eric Potma）发表了题为“中红外非线性光学显微镜”的主题演讲，并在历史名镇鲁昂举行了欢迎酒会之后，常规的科学计划于周一早晨在CORIA设施开始。会议期间进行了六次受邀演讲，随后进行了口头演讲和海报发布会。主要社交活动包括在鲁昂历史中心的带导游的参观以及在历史悠久的Halle aux Toiles的会议晚宴。

《拉曼光谱学杂志》的这一特别部分构成了在ECONOS / ECW 2019上发表的五篇论文的精选。由于会议范围广泛，这些论文涵盖了广泛的方法及其在各种系统中的应用。

非线性光学光谱学的应用传统上涵盖了物质的所有状态，这也反映在本期特刊中。其中有四篇论文涉及微观技术。Gagliardi等。^[ 1 ^]在基本的CARS实验中研究了一种流行类型的光子晶体光纤发射的超连续谱的红外部分。通过统计方法评估了参比环己烷样品的SC辐射和CARS信号对激光操作条件的依赖性。数据揭示了明确的相关性，据信这是一般性的，具有广泛的适用性。Lanin等。^[ 2 ^]演示了单光束光遗传多峰非线性光学显微镜的方法。为此，他们结合了三次谐波产生和三光子激发荧光。在脑切片和细胞培养物中进行的实验表明，显微技术可用于HeLa系癌细胞衍生物以及深脑神经元和星形胶质细胞的线粒体和体细胞内结构的亚细胞分辨率，高对比度成像。De la Cadena等。^[ 3 ^]引入了一种高灵敏度宽带激发拉曼散射装置，用于低波数范围（<500 cm ^-1的显微光谱））。该系统将窄带斯托克斯脉冲与宽带泵浦脉冲结合在一起，并使用检流镜快速扫描受激拉曼损耗信号。已证明该装置能够测量几种溶剂的光谱，并能够获得由聚合物珠测试样品的显微图像以及植物细胞壁内不同生物物质的分布组成的高光谱数据立方体。Arzumanyan等。^[ 4 ^]运用拉曼光谱技术来区分NETosis期间转化的嗜中性粒细胞，并定量测定其转化水平。为此，分析了从人血样品中不同转化水平获得的嗜中性粒细胞拉曼光谱。他们实现了在不同转化水平下嗜中性粒细胞拉曼光谱的光谱原型中统计学上显着差异的检测。

气相应用也是ECONOS / ECW涵盖的传统领域。张等。^[ 5 ^]在分子束中产生Cu二聚体，并对其应用了双色共振四波混合光谱。从他们的实验中，他们报告了对双铜的0 ⁺ _g激发态的首次观察。通过从基态直接吸收单光子无法观察到这种状态，因此使用非线性光学现象是进行此类研究的前提。

此ECONOS / ECW特别部分重点介绍了非线性光学光谱学及其在整个科学和工程学科中的应用领域的不断发展。科学界的热情和创造力以及新颖和改进的实验设备的迅速发展将确保非线性光谱学研究的美好前景。