A number of optical systems depend upon diffraction gratings to resolve light into advantageous spectra by splitting light via dispersion into its component wavelengths. Polychromatic light is dispersed into its constituent colors by traditional reflection gratings utilizing a series of parallel rulings, precision engineered to have the appropriate dispersion efficiency profile by ensuring close control of the distance between these adjacent grooves and their individual angles.
The rays of the incident beam interact with this periodic structure, which causes interference and dispersion of the output beam. Transmission gratings function on the same fundamental principle of interference via a periodic structure and transmit the diffracted light to facilitate the development of smaller, lens-based optical designs.
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Manufacturers regularly make efforts to produce gratings optimized for particular end-use scenarios, predicated on essential parameters including wavelength range, resolution, signal polarization, simultaneous bandpass, and decreased device footprint. Volume phase holographic (VPH) transmission gratings are a high-performance substitute compared to traditional ruled surface relief reflection gratings. Moreover, Wasatch Photonics’s novel VPH technology delivers exceptional design flexibility to meet the performance objectives for a wide range of applications.
In this article, five well-known applications of transmission gratings will be discussed.
1. Pulse Compression Gratings
Pulse compression gratings are utilized in laser applications to compress or stretch ultrafast laser pulses with extremely high transmission rates at a single polarization. Wasatch Photonics can provide polarization-enhanced designs with exceptional uniformity and reduced scattering when compressing laser pulses on either the femto- or picosecond regimes. Each grating has been produced with the necessary low wavefront error required to sustain beam uniformity and optimize pulse power.
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2. UV-Vis, NIR, and Raman Spectroscopy Gratings
Transmission gratings demonstrating extensive bandwidth competencies across the ultraviolet-visible (UV-VIS) or near-infrared (NIR) regions of the electromagnetic spectrum are well-suited for low-light spectroscopic applications. These provide enhanced detection of relatively weak signals such as Raman scattering and fluorescence. A transmission configuration for these applications also allows for more inclusive corrections of aberrations and a thermally stable, compact footprint.
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3. Hyperspectral Imaging Transmission Gratings
Hyperspectral imaging is an advanced form of RGB multi-color spectral imaging that can simultaneously detect a continuum of spectral lines. This requires transmission gratings with the greatest efficiency possible and low polarization dependence over an exceptionally broad wavelength range, as well as low wavefront error, to conserve the clarity of the image. Transmission gratings also allow for straight-pass optical designs to acquire hyperspectral imaging, have a small footprint and are easy to align using grisms (a combination of grating and prism).
Image Credit: Wasatch Photonics, Inc.
4. Transmission Gratings in Astronomy
More than any other field of study, astronomical optics demands precision to reduce image distortion in conditions and environments that experience extremely low levels of light to capture detailed spectra from objects that could be light years away. VPH transmission gratings provide high-line frequencies and broadband performance, meaning an even wider range can be covered due to angle-tuned capabilities. These are generally employed in large telescopes, where a suite including a number of large gratings (up to 30 centimeters in size) may be employed to cover the required spectral range.
Image Credit: Wasatch Photonics, Inc.
5. OCT Imaging Transmission Gratings
Spectral domain optical coherence tomography (SD-OCT) is an excellent technique typically employed for the visualization of sub-surface tissue structures in three-dimensions utilizing visible or near-infrared (NIR) light, and is predominantly used for both medical diagnostics and non-destructive testing. OCT demands high signal-to-noise control over an extensive bandwidth to create high-resolution images over the complete working depth of the system. Transmission gratings developed for OCT are optimized at all polarizations, even at the bandwidth extremes, for greater transmission efficiency, generating reduced SNR roll-off and clearer, deeper OCT images.
Image Credit: Wasatch Photonics, Inc.
Transmission Gratings from Wasatch Photonics
Wasatch Photonics develops and supplies an extensive range of high-efficiency transmission gratings that are readily available for standardized applications. Wasatch Photonics also has the expertise for developing custom designs and manufacturing novel transmission grating solutions to meet customer specifications. Contact Wasatch Photonics today to discuss your specific needs.
This information has been sourced, reviewed and adapted from materials provided by Wasatch Photonics, Inc.
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