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

Optical pulses as short as 103 fsec at 695 nm and 263 fsec at 733 nm have been generated in synchronously pumped hybrid Pyridine 1 and Pyridine 2 cw dye lasers, respectively, both using the saturable absorber 1,1′-diethyl-2,2′-dicarbocyanine iodide (DDI). These results combine with other data from the same linear cavity to give direct femtosecond generation over the spectral range 560–840 nm.

Femtosecond synchronously pumped Pyridine dye lasers.

This article reviews the generation and amplification of ultrashort laser light pulses, τp≤10−12 s. Current methods for generating optical pulses in the ultraviolet, visible, and infrared regions of the spectrum are described. Devices based on mode‐locking techniques, as well as various novel sources for ultrashort light pulses, are examined. In addition, recent advances in using fiber optics to shape and compress optical pulses are presented. Optical amplifiers that have been developed to generate kilowatt and higher peak powers at a variety of repetition rates are described and compared. In the last section of the paper, various nonlinear optical techniques that have been developed to extend the tuning range of ultrashort laser pulses are briefly discussed.

Ultrashort light pulses

Chapter 3 – FEMTOSECOND DYE LASERS

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.

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

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

A mode-locked dye laser in conjunction with a synchronously operating streak camera has been used to study ultrashort light pulse propagation in a weakly multimode optical fibre. Measurements of the intermodal temporal dispersion allowed the effective core radius a, the refractive index difference Δ and the cutoff wavelengths of the LP21 and LP11 mode groups to be determined. The LP21 cutoff wavelength was experimentally verified and the temporal dispersion of the LP01 and LP11 mode groups investigated as a function of the fibre length.

Streak camera study of ultrashort pulse propagation in a weakly multimode optical fibre

Passive mode-locking of a c.w. rhodamine 700 dye laser is reported for the first time. Continuous output trains of subpicosecond pulses have been obtained with two saturable absorber dyes, DOTCI and HITCI, in the 727–740 nm and 762–778 nm spectral regions respectively. By the addition of a fast recovery time dye (DCI) to the DOTCI saturable absorber solution, pulses as short as 350 fs at 740 nm have been generated in a linear cavity configuration.

N. Langford

Papers

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

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

Streak camera study of ultrashort pulse propagation in a weakly multimode optical fibre

A Passively Mode-locked c.w. Rhodamine 700 Dye Laser