Technical Notes

PGL’s expanding library of technical notes explains the fundamentals of diffraction gratings with an emphasis on laser applications.

Fundamentals

The Grating Equation

Diffraction gratings can be understood using the optical principles of diffraction and interference. When light is incident on a surface with a profile that is irregular at length scales comparable to the wavelength of the light, it is reflected and refracted at a microscopic level in many different directions as described by the laws of diffraction. If the surface irregularity is periodic, such as a series of grooves etched into a surface, light diffracted from many periods in certain special directions constructively interferes, yielding replicas of the incident beam propagating in those directions. Learn More »

Angular Dispersion

Gratings are special because they introduce dispersion to the diffracted light waves. A wave experiences dispersion when one of its features, such as velocity or direction, depends on its frequency or, equivalently, its wavelength. Perhaps the most widely used dispersive property of gratings is angular dispersion—the fundamental enabler for most spectroscopy measurements and instruments. Learn More »

Temporal Dispersion

Gratings are special because they introduce dispersion to the diffracted light waves. A wave experiences dispersion when one of its features, such as velocity or direction, depends on its frequency or, equivalently, its wavelength. Gratings are widely used to introduce a frequency-dependent time delay for short laser pulses. Chirped Pulse Amplification (CPA) is based on stretching and compressing after amplification short pulses using temporal dispersion from two or more gratings. Learn More »

Dispersion and Pulses

Many optical systems and experiments involve signals which vary fairly rapidly in time. A short burst of light—referred to as a pulse—might be used to carry information, as in an optical fiber communications system, or to achieve a high peak intensity for applications ranging from materials processing to high-intensity physics research. Learn More »

Diffraction Efficiency

Diffraction gratings can be understood using the optical principles of diffraction and interference. How much light diffracts into each direction is determined by the principle of diffraction at a microscopic level. In other words, the profile of the grating grooves dictates the efficiency with which light diffracts into each of the orders. Learn More »

Applications

Gratings for High-average-power Ti:Sapphire Laser Systems

A large number of high-average-power (HAP) petawatt-class lasers are in early development stages around the world. In comparison to existing petawatt lasers that operate at low repetition rates (typically below 1 Hz), these new HAP lasers are expected to deliver pulse energies > 1 Joule at repetition rates > 1 kHz, producing average powers up to 100’s of kW. Many of these will operate with pulse durations below 10’s of fs, thus requiring spectral bandwidths of up to 100 nm or higher. These combined requirements exceed what is possible with the current state-of-the-art in pulse-compression diffraction grating technology. In this technical note we consider limitations and trade-offs associated with gold gratings (used in most existing petawatt lasers) and multilayer dielectric (MLD) gratings. Learn More »
Plymouth Grating Laboratory is dedicated to making the highest-quality diffraction gratings available today. Our focus is on lasers and laser systems. PGL gratings offer exceptionally high diffraction efficiency and laser damage threshold, combined with superior wavefront error and uniformity over large areas. This performance is made possible by PGL’s exclusive use of the Nanoruler, based on the proprietary Scanning Beam Interference Lithography technology developed at MIT, and PGL’s industry-leading process expertise. The company occupies 20,000 sq. ft. of dedicated manufacturing, engineering, and office space in Carver, MA, just outside of Plymouth, and about 45 miles south of Boston.

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