Continuous progress in the development of light sources for the generation of tunable ultrashort pulses from the near-infrared to all the visible range provides a very efficient tool for spectroscopic techniques able to follow ultrafast dynamical processes in matter. Second-order nonlinear optical processes like Optical Parametric Amplification (OPA) have demonstrated the capability of generating light pulses with durations down to few cycles of the carrier wave. The aim of this paper is to introduce the basic concepts for the generation of tunable ultrashort pulses and show their application to ultrafast spectroscopy. We will discuss the principles of parametric amplification and the main criteria for the design of broadband OPAs; we will also illustrate some of the schemes providing ultrashort pulses in the spectral ranges from the ultraviolet to the infrared, offering a comprehensive overview of the state of the art of the current research activity in this rapidly evolving field. An important requirement for the applications of ultrashort pulses is the capability to measure the amplitude and phase of their electric field; we will discuss a rich ensemble of spectrographic, interferometric or phase-scanning techniques for the temporal characterization of ultrashort pulses. Pump-probe techniques with broadband pulses and more recently two-dimensional spectroscopic techniques allow to follow in great detail complex dynamical processes. The few examples reported in this review just provide a sample of what is already a vast class of ultrafast phenomena, which can be studied nowadays in real time.

中文翻译：

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可调谐的少光周期脉冲和先进的超快光谱技术

用于从近红外到所有可见光范围产生可调超短脉冲的光源开发方面的不断进步，为光谱技术提供了一种非常有效的工具，能够遵循超快速动力学过程。二阶非线性光学过程（如光学参量放大（OPA））证明了产生光脉冲的能力，其持续时间低至载波的几个周期。本文的目的是介绍可调超短脉冲生成的基本概念，并展示其在超快光谱学中的应用。我们将讨论参数放大的原理以及宽带OPA设计的主要标准；我们还将说明一些方案，这些方案在从紫外线到红外的光谱范围内提供超短脉冲，从而全面概述了这个快速发展领域中当前研究活动的最新技术水平。应用超短脉冲的一个重要要求是能够测量其电场的幅度和相位。我们将讨论用于超短脉冲的时间表征的丰富的光谱，干涉或相位扫描技术集合。带有宽带脉冲的泵浦探测技术和最近的二维光谱技术使我们可以非常详细地跟踪复杂的动力学过程。这篇评论中报道的几个例子仅提供了已经属于一大类超快现象的样本，