What Is an Ultrashort Pulse Laser?
An ultrashort pulse laser is a type of laser with extremely brief pulse widths ranging from a few picoseconds to a few femtoseconds. A picosecond is one trillionth of a second, while a femtosecond is even shorter, at one quadrillionth of a second. The extreme brevity of these pulses means that in the time it takes for a single pulse to occur, light travels only a fraction of a millimeter.
This short pulse duration makes ultrashort pulse lasers unique among pulsed lasers. These lasers produce a pulse that undergoes a large change in a very brief period, allowing for high-precision, low-thermal-impact laser processing across a wide range of materials.
Uses of Ultrashort Pulse Lasers
Ultrashort pulse lasers are particularly effective due to their high peak intensity, allowing them to interact even with transparent materials through nonlinear absorption processes like multiphoton ionization. By focusing these laser beams inside transparent materials, intricate, three-dimensional processing becomes possible.
They can be used on various materials, from hard diamonds to softer materials like glass, resins, and ceramics. The precision of ultrashort pulse lasers allows for detailed processing such as drilling, trimming, and micro-texturing without causing heat damage or burrs.
Principle of Ultrashort Pulse Lasers
Lasers can oscillate continuously (CW lasers) or in pulses. Pulsed lasers, including ultrashort pulse lasers, operate intermittently and can be modulated in various ways, such as direct, external, Q-switching, or mode-locking. Ultrashort pulse lasers typically use the mode-locking method to achieve their incredibly brief pulse widths.
Mode-Locking Method
Mode-locking can be active (forced) or passive (self-mode-locking). Active mode-locking synchronizes the phase between modes using a loss or phase modulator, while passive mode-locking uses a saturable absorber to selectively absorb the leading edge of a pulse. Both methods are essential for producing ultrashort pulse lasers.
Pricing of Ultrashort Pulse Lasers
Due to their complex design and short pulse widths, ultrashort pulse lasers are among the more expensive laser types. They are used in various applications, from microfabrication to scientific research, and typically fall in the higher price range.
History of Ultrashort Pulse Lasers
The development of lasers began with ruby lasers in the 1960s, which used pulsed oscillation. Over time, innovations like the Q-switch method and mode-locking have led to the advancement of laser technology, enabling the creation of lasers capable of producing extremely short pulses, including picosecond and femtosecond lasers.
Q-Switch Method
The Q-switch method produces high-power pulses over microseconds to nanoseconds. This method temporarily suppresses laser oscillation, building up energy before releasing it in a powerful pulse, and is used in various applications, including electronic and semiconductor processing.
YAG Laser
The YAG laser is a solid-state laser using yttrium aluminum garnet as the medium. It’s known for its manageability and efficiency in processing.
Dye Laser
Dye lasers use a liquid dye solution as the lasing medium, offering a wide range of wavelength variability and applications, including medical and industrial uses.
The evolution of these lasers over the years has led to the development of Ti: sapphire lasers and other advanced femtosecond laser systems, further expanding the capabilities and applications of ultrashort pulse lasers.