Methods of Experimental Physics.

Summary form only given. This article is intended to provide an introduction to ultrafast laser development for scientists new to the field. It also aims to provide a snapshot of the state-of-the-art of ultrafast lasers and to indicate how this state evolved over the last thirty years. In the first section, the main issues concerning ultrashort pulse generation are discussed and the most important ultrafast laser media are briefly reviewed, An extensive historical survey of mode-locking and pulse compression from 1964 until 1994 is then presented which covers the most important developments and aims to put recent advances and state-of-the-art femtosecond lasers in context. This review also anticipates future developments in practical ultrafast lasers for real-world applications, The basic techniques of mode-locking are then reviewed at a tutorial level. These include active mode-locking, passive mode-locking with real, resonant saturable absorbers and passive mode-locking with the optical Kerr effect. Emphasis is placed on ultrafast solid-state lasers, dye lasers and fibre lasers. Group velocity dispersion and self-phase modulation are introduced and their interaction discussed in some detail, Fibre-optic pulse compression is described and the significance of soliton shaping and solitary lasers is highlighted. Some of the phenomena limiting the minimum achievable duration of laser pulses are identified. The final section describes techniques for measuring ultrashort pulses including electrooptic streak cameras and second harmonic generation autocorrelation.

https://iopscience.iop.org/article/10.1088/0034-4885/58/2/001/pdf

The generation of ultrashort laser pulses

The passive and hybrid Q-switching and mode-locking of solid-state lasers, dye lasers, semiconductor lasers and gas lasers is reviewed. The dynamics of saturable absorbers and reverse saturable absorbers is illustrated. The nanosecond pulse generation by passive and hybrid Q-switching of low-gain active media is described. The picosecond and femtosecond pulse generation by passive and hybrid mode-locking in low-gain and high-gain active media is analysed. The performance data of passively and hybridly mode-locked cw femtosecond dye lasers are collected. The pulse shortening of ultra-fast pulses with saturable absorbers in intra-cavity and extra-cavity configurations is discussed.

/pdf/passive-q-switching-and-mode-locking-for-the-generation-of-59azkkaa4g.pdf

Passive Q-switching and mode-locking for the generation of nanosecond to femtosecond pulses

Ultrashort laser pulses are finding increasing application in numerous branches of science and technology. This article is an attempt to provide a comprehensive review of the whole field of ultrashort pulse generation, covering both the experimental and the theoretical aspects of the subject. By far the commonest method of generating pulses in the picosecond and subpicosecond regime is the technique known as 'mode-locking' and it is with this that the review is therefore largely concerned. After introductory remarks and a simple treatment of some of the general principles, the central sections of the review deal with the main generic techniques, namely spontaneous mode-locking, active mode-locking (including mode-locking by synchronous pumping) and passive mode-locking. Within each section the material is organised into three main categories, namely (a) general background, (b) historical survey (mainly relating to experimental work and densely packed with references to published work) and (c) theoretical methods (presented with a strongly pedagogical flavour). A major section at the end deals with a mass of important (and mostly recent) work that does not fit naturally into the main framework of the review. This includes USP generation in semiconductor lasers, a number of special methods such as injection mode-locking (and others where two or more mode-locking techniques are combined), as well as chopping and switching techniques.

http://iopscience.iop.org/article/10.1088/0034-4885/46/8/001/pdf

Numerical simulations tracing the pulse evolution in the case of mode locking by synchronous pumping are presented. It is argued that strictly steady-state pulses are impossible in principle because the wings of the pulses are embedded in background radiation generated by spontaneous emission. The simulations demonstrate that the perturbations introduced by the stochastic background can be severe, and that these can apparently be minimized only at the expense of the overall quality of the mode-locked pulse envelopes.

Role of spontaneous emission in the dynamics of mode locking by synchronous pumping

Passive mode locking of a cw Rhodamine 700 dye laser is reported for the first time to our knowledge. By using two saturable absorber dyes, DOTCI and HITCI, continuous-output trains of subpicosecond pulses have been obtained in the 727–740- and 762–778-nm spectral regions, respectively. By the addition of a fast-recovery-time dye (DCI) to the DOTCI saturable absorber, pulses as short as 350 fsec at 740 am have been generated.

K. Smith

Papers

Passive mode locking of a continuous-wave dye laser in the red-near-infrared spectral region

Simultaneous autocorrelation and synchroscan streak camera measurement of cavity length detuning effects in a synchronously pumped cw dye laser

Subpicosecond generation via hybrid mode-locking of styryl 9 in the near infra-red

Comparison of experiment and theory in a synchronously mode-locked dye laser

The hybrid mode-locking of a cw Rhodamine 700 dye laser