Femtosecond laser micromachining can be used either to remove materials or to change a material's properties, and can be applied to both absorptive and transparent substances. Over the past decade, this technique has been used in a broad range of applications, from waveguide fabrication to cell ablation. This review describes the physical mechanisms and the main experimental parameters involved in the femtosecond laser micromachining of transparent materials, and important emerging applications of the technology. Interactions between laser and matter are fascinating and have found a wide range of applications. This article gives an overview of the fundamental physical mechanisms in the processing of transparent materials using ultrafast lasers, as well as important emerging applications of the technology.

Femtosecond laser micromachining in transparent materials

Fibre lasers in the mid-infrared regime are useful for a diverse range of fields, including chemical and biomedical sensing, military applications and materials processing. This Review summarizes the different rare-earth cations and host materials used in mid-infrared fibre laser technology, and discusses the future applications and challenges for the field.

Towards high-power mid-infrared emission from a fibre laser

The unique characteristics of ultrafast lasers, such as picosecond and femtosecond lasers, have opened up new avenues in materials processing that employ ultrashort pulse widths and extremely high peak intensities. Thus, ultrafast lasers are currently used widely for both fundamental research and practical applications. This review describes the characteristics of ultrafast laser processing and the recent advancements and applications of both surface and volume processing. Surface processing includes micromachining, micro- and nanostructuring, and nanoablation, while volume processing includes two-photon polymerization and three-dimensional (3D) processing within transparent materials. Commercial and industrial applications of ultrafast laser processing are also introduced, and a summary of the technology with future outlooks are also given. Scientists in Asia have reviewed the role of ultrafast lasers in materials processing. Koji Sugioka from RIKEN in Japan and Ya Cheng from the Shanghai Institute of Optics and Fine Mechanics in China describe how femtosecond and picosecond lasers can be used to perform useful tasks in both surface and volume processing. Such lasers can cut, drill and ablate a variety of materials with high precision, including metals, semiconductors, ceramics and glasses. They can also polymerize organic materials that contain a suitable photosensitizer and can three-dimensionally process inside transparent materials such as glass, and are already being used to fabricate medical stents, repair photomasks, drill ink-jet nozzles and pattern solar cells. The researchers also explain the characteristics of such lasers and the interaction of ultrashort, intense pulses of light with matter.

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Ultrafast lasers—reliable tools for advanced materials processing

High-repetition rate femtosecond lasers are shown to drive heat accumulation processes that are attractive for rapid writing of low-loss optical waveguides in transparent glasses. A novel femtosecond fiber laser system (IMRA America, FCPA muJewel) providing variable repetition rate between 0.1 and 5 MHz was used to study the relationship between heat accumulation and resulting waveguide properties in fused silica and various borosilicate glasses. Increasing repetition rate was seen to increase the waveguide diameter and decrease the waveguide loss, with waveguides written with 1-MHz repetition rate yielding ~0.2-dB/cm propagation loss in Schott AF45 glass. A finite-difference thermal diffusion model accurately tracks the waveguide diameter as cumulative heating expands the modification zone above 200-kHz repetition rate.

Heat accumulation effects in femtosecond laser-written waveguides with variable repetition rate.

Nonlinear Optical Crystals: A Complete Survey

A 50 W sub-picosecond fiber chirped pulse amplification system generating 50 µJ pulses at a repetition rate of 1 MHz is demonstrated. As required for precision high speed micro-machining, this system has a practical system configuration enabled by the fiber stretcher and 1780 l/mm dielectric diffraction grating compressor and is capable of ablation rates >0.17 mm3/s metal, ceramic, and glass.

Micromachining with a 50 W, 50 muJ, subpicosecond fiber laser system.

Laser action in Yb3+:YCOB (Yb3+:YCa4O(BO3)3)

We report efficient, diode-pumped, self-frequency doubling (SFD) in the newly developed laser crystal Nd3+:YCa4O(BO3)3. More than 350 mW of fundamental output power at 1060 nm was achieved with a slope efficiency of 51%. With one watt of absorbed pump power, 62 mW of green cw laser emission at 530 nm was observed with proper phase matching. This initial performance, and the good optical properties of the crystalline host, are encouraging for the development of a high power diode-pumped SFD visible light laser source.

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Diode-pumped self-frequency doubling in a nd3+:yca4o(bo3)3 laser

We report the first implementation of a 2 μm thulium fiber laser in a Laser-Induced Breakdown Spectroscopy system. Emission from plasma on copper samples was analyzed from 200 to 900 nm. The low ablation fluence (<100 J.cm−2) and 200 ns pulse duration lead to a plasma with neither continuum emission, nor air emission in the near-infrared region.

Lawrence Shah

Papers

Micromachining with a 50 W, 50 muJ, subpicosecond fiber laser system.

Laser action in Yb3+:YCOB (Yb3+:YCa4O(BO3)3)

Diode-pumped self-frequency doubling in a nd3+:yca4o(bo3)3 laser

Laser-induced breakdown spectroscopy of copper with a 2 μm thulium fiber laser

Investigation of diode-pumped, self-frequency doubled RGB lasers from Nd:YCOB crystals