![]() This process is repeated until damage is observed. Next, the power/energy is either increased or decreased and the optic is exposed at 10 new locations. The number of locations that are damaged at a particular power/energy level is recorded. After exposure, the optic is examined by a microscope (~100X magnification) for any visible damage. The optic is exposed in 10 locations to this laser beam for 30 seconds (CW) or for a number of pulses (pulse repetition frequency specified). Thorlabs' LIDT testing is done in compliance with ISO/DIS 11254 and ISO 21254 specifications.įirst, a low-power/energy beam is directed to the optic under test. For more information on cleaning optics, please see our Optics Cleaning tutorial. Because dust or other particles on the surface of an optic can cause damage at lower thresholds, we recommend keeping surfaces clean and free of debris. Note that the guideline presented here assumes room temperature operation and optics in new condition (i.e., within scratch-dig spec, surface free of contamination, etc.). Pulsed lasers, on the other hand, often strip electrons from the lattice structure of an optic before causing thermal damage. Continuous wave (CW) lasers typically cause damage from thermal effects (absorption either in the coating or in the substrate). The LIDT for an optic greatly depends on the type of laser you are using. When choosing optics, it is important to understand the Laser Induced Damage Threshold (LIDT) of the optics being used. The following is a general overview of how laser induced damage thresholds are measured and how the values may be utilized in determining the appropriateness of an optic for a given application. The specifications to the right are measured data for Thorlabs' Echelle Diffraction Gratings. Often a dispersing prism is used in combination with an Echelle grating for order sorting.ĭamage Threshold Data for Thorlabs' Echelle Gratings The disadvantage is the reduced free spectral range, which decreased from 630 nm (630 nm/1) to 15.8 nm (630 nm/40). From the equation above, at n=1 the angular separation is 0.009° but at n=40 the angular separation 0.6°. ![]() Imagine two lines, one at 600 nm and the other at 605 nm, incident on a grating with 31.6 lines/mm. In the simplest case where light is incident on the grating at an angle of 0° the grating equation simplifies to nλ = d sin θ' and if solved for sin θ' it becomes:įrom this it follows that in higher orders the angular separation between two wavelengths becomes greater. Using an Echelle Grating: The extremely high blaze angle of the Echelle grating concentrates the energy in the higher orders. If λ1 and λ2 are lower and upper limits, respectively, of the band of interest, then: As grating spacing decreases, the free spectral range increases. The Grating Equation: The general grating equation may be written as: nλ = d(sin θ + sin θ') where n is the order of diffraction, λ is the diffracted wavelength, d is the grating constant (the distance between grooves), θ is the angle of incidence measured from the normal and θ' is the angle of diffraction measured from the normal.įree Spectral Range: Free spectral range is the maximum spectral bandwidth that can be obtained in a specified order without spectral interference (overlap) from adjacent orders. ![]() If your application requires integrating the grating into a sub-assembly or a setup please contact us to learn more about our assembly capabilities. ![]() ![]() Thorlabs uses a clean room facility for assembly of gratings into mechanical setups. Solvents will likely damage the grating's surface. No attempt should be made to clean a grating other than blowing off dust with clean, dry air or nitrogen. Latex gloves or a similar protective covering should be worn to prevent oil from fingers from reaching the grating surface. Gratings should only be handled when necessary and always held by the sides. The surface of a diffraction grating can be easily damaged by fingerprints, aerosols, moisture or the slightest contact with any abrasive material. Gratings can also be mounted in one of three Kinematic Grating Mount Adapters which can be used with any of Thorlabs' Ø1" Mirror Mounts, including the POLARIS-K1E Ultra-Stable Kinematic Mirror Mount. All of Thorlabs' gratings can be mounted directly into the KM100C Right-Handed or KM100CL Left-Handed Kinematic Rectangular Optic Mount. Thorlabs offers a variety of mounts and adapters for precise and stable mounting and aligning of square optics. Diffraction Grating Mounted in Polaris Mirror Mount Using Diffraction Grating Adapter Mounts and Adapters ![]()
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