A miniaturized double-pulse device using deep-etched gratings has been demonstrated in Shanghai Institute of Optics and Fine Mechanics.

Researchers at Shanghai Institute of Optics and Fine Mechanics (SIOM) invented a miniaturized device composed of two deep-etched gratings for generation of double pulses. According to the group, this miniaturized device provides an easy way of generating two pulses which can be tuned by moving the distance between two gratings.

Splitting one femtosecond laser pulse into two is an essential requirement in almost every applied field of femtosecond laser, such as micromachining, measurement, etc.. A Michelson structure is widely used, which is composed of one beamsplitter, two reflective mirrors, etc. But its size is large, and its cost is high. In addition, high laser damage threshold of such a device is crucial for its practical applications in high power laser system.

“We developed a simple and compact device that can generate double pulses of femtosecond laser”. said by Prof. Changhe Zhou, the team leader at the Shanghai Institute of Optics and Fine Mechanics, "One of the most attractive advantages of this device is its high laser damage threshold because it is composed of two fused silica gratings. Another one is that the whole size of this device is quite small, only severalmillimeters in thickness, and several tens millimeters in aperture depending on the laser beam size, which is much smaller than a usual Michelson beam splitter. The price can be low due to the mass production”.

This device is transparent with little reflection. A Michelson structure would easily reflect some of the incident beam back to the laser oscillator when the reflective mirror is aligned, which would cause the laser output instable. It should be noted that polarization isolator could solve this problem, but it would increase the cost, make the system complex.　

“Using this device, it would not cause such a problem”, said by Prof. Changhe Zhou, “In addition, this device is almost polarization-indepedent, which is also beneficial”.

One more interesting thing is that this device is switchable between two pulses and one pulse, when there is a relative movement between two gratings with a 1/4 period, the second pulse would disappear and this device generates only one pulse. This device provided new opportunities for developing novel optical elements and systems for a variety of practical applications.

This experimental result has been published in Applied Optics49, 4506-4513(2010). The reviewer of this paper commented that“proposed apparatus can find some niche in application of femtosecond lasers”. Related papers about the deep-etched gratings can be found in Applied Optics 49, 4108-4112(2010); Applied Optics 49, 1739-1743(2010); Applied Optics 49, 5697-5704(2010); Applied Optics 47, 6638-6643 (2008).