The equation is stated as follows: The magnification equation relates the ratio of the image distance and object distance to the ratio of the image height (hi) and object height (ho). I would need to know how thick is the protective layer. Benjamin. The spreadsheet will then calculate a linear power density for CW and pulsed systems, as well as an energy density value for pulsed systems. Is this damage caused by average or by peak power? Then place the mirror so that it reflects to the camera the same target area just photographed. Any image that is upright and located behind the mirror is considered to be a virtual image. As described on the previous tab, LIDT values in the nanosecond pulse regime scale with the square root of the laser pulse duration: This adjustment factor results in LIDT values of 0.45 J/cm2 for the BB1-E01 broadband mirror and 1.6 J/cm2 for the Nd:YAG laser line mirror, which are to be compared with the 0.7 J/cm2 maximum energy density of the beam. Can you please confirm the reflectance percentage from ~1 to 10um for both protected silver and protected aluminum of your products? I am interested in phase shifts in the range 600 - 900 nm at 45 AOI, if you wish to send me the data directly. The general expression for reflectivity is derivable from Fresnel's Equations. Response from Bweh at Thorlabs USA: Thanks for bringing this to our attention. I will reach out to you with this data. The 2µm wavelength regime is useful for surgical procedures as it can target discrete depth levels of tissue beneath the skin’s surface. Thank you. Maximum diffusion is the watchword; this can be attained by clever illumination arriving from other than a small-angle source. I am using the PFSQ10-03-P01 mirror. Thanks in advance, Andrea Fioretti. Normal Reflection Coefficient The reflectivity of light from a surface depends upon the angle of incidence and upon the plane of polarization of the light. I will send you data of the phase shift generated by these silver coated mirrors. Be aware of issues of directionality in scatter, which typically results in stronger intensity on a sightline to the light source. Encyclopedia … combined with a great Buyer's Guide! Maria, Dear Sir or Madam, 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. In addition, our 35 mm x 52 mm mirror is specifically designed for use with the Cerna® Breadboard Top with Two-Position Slider for DIY microscopy. If you are really fussy calibrated aluminised specular reflectance standards are available. TECHSPEC® Laser Line Mirrors offer >99.98% reflectivity at 1064nm and high damage thresholds of up to 6 J/cm2 @ 355nm. Si layer, respectively. Thanks. Due to their high reflectance over the 450 nm - 20 µm range, these mirrors are well suited for use with femtosecond pulsed lasers. 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). ZINGER: 6. Except for the Ø0.28" (Ø7 mm) and 35 mm x 52 mm sizes, each mirror has been engraved with the item number on the back of the substrate for easy identification in the lab. TECHSPEC® Laser Line λ/20 High Tolerance Right Angle Mirrors feature >99.5% reflectivity at Nd:YAG wavelengths. Pulsed Microsecond Laser ExampleConsider a laser system that produces 1 µs pulses, each containing 150 µJ of energy at a repetition rate of 50 kHz, resulting in a relatively high duty cycle of 5%. Measure standard, measure mirror, measure dark signal, calculate mirror reflectance. Note that the apparent bandwidth of the resonances, observed e.g. Please see the Graphs tab above for reflectance curves. These values are used to calculate adjusted, scaled LIDT values for the optics based on accepted scaling laws. The best technique to determine reflectivity depends on the reflectivity level and application requirements. You must now consider hotspots in the beam or other non-uniform intensity profiles and roughly calculate a maximum power density. for both p and s polarization? It is common industry practice to determine mirror reflectivity by measuring transmission using spectrophotometry and assuming that the rest of the light was reflected. Community Forum Software by IP.BoardLicensed to: Cloudy Nights, This is not recommended for shared computers, binoculars vs a telescope of higher aperture and faster speed, Harmonic Reed Starmaster "Giant" Telescope, starting to love this automation stuff - sleeping on a horsehead. Is mirror surface flatness specified as Peak-to-Valley or RMS value? Unfortunately, this is highly dependent on factors such as absorption and thermal diffusivity, so there is no reliable method for determining when a high PRF laser will damage an optic due to thermal effects. Anti-reflection coatings are used to diminish the losses. It is standard industry practice for optical component suppliers to verify the reflectivity of mirrors by using a spectrophotometer to directly measure transmission. (See also our privacy declaration.) An applications engineer from our team in China will reach out to you directly. I followed this formula to calculate my reflectivity: ... is I don't know which parameters refer to which. One is specular reflectance (ρs) and the second is diffuse reflectance (ρd). The number of locations that are damaged at a particular power/energy level is recorded. Therefore, a high spectral resolution in a wide spectral range is possible. Average linear power density can be calculated using the equation below. Contact Tech Support for more information. 1.22 % Contrast Ratio. This can be compared to the LIDT values for a WPQ10E-980 polymer zero-order quarter-wave plate, which are 5 W/cm for CW radiation at 810 nm and 5 J/cm2 for a 10 ns pulse at 810 nm. The following NIST paper illustrates the geometry and setup for measuring specular reflectance with an integrating sphere; Although this is for the infrared the setup is the same (apart from the detector) for the visible. Can some information be given regarding how this mirror coating holds up to femtosecond pulses? The calculation above assumes a uniform beam intensity profile. A response from Adam to gsh: We can certainly add this data to the website. Here you go. Again, a negative or positive sign in front of the numerical value for a physical quantity represents information about direction. The solution is shown below. Here is how NIST measures the reflectivity of flat samples: A variant of this is probably how the microscan system does it. Measuring its reflectance directly by using reflectance spectrophotometry showed that Mirror 2 has much worse performance and a trailing reflectance that drops to 0.5% less than that of Mirror 1 due to absorption and scattering (Figure 3). As a guideline, lasers with pulse duration in the range of 10 ns to 10 us can cause damage by dielectric breakdown and by thermal absorption. use to determine the actual reflectivity of the mirror. Hello. For reference, a Gaussian beam typically has a maximum power density that is twice that of the uniform beam (see lower right). I would also like to be able to measure the reflectivity of the larger secondaries...but that is a secondary consideration (groan for the pun.) For long pulses to CW, linear power density becomes a constant with spot size. In the meantime, I will email you the data you are looking for. The energy density of your beam should be calculated in terms of J/cm2. 4. As previously stated, pulsed lasers typically induce a different type of damage to the optic than CW lasers. Response from Jeremy at Thorlabs: We do not have comprehensive data on this available at the moment but we can share some preliminary test data. As before, the CW LIDT of the optic scales linearly with the laser wavelength, resulting in an adjusted CW value of 6 W/cm at 980 nm. The integrating sphere is the device that makes it all possible. thanks. One can also change the geometry to measure scattered light - if this is too large the mirror needs to be cleaned. A magnified, inverted image is located a distance of 32.0 cm from a concave mirror with a focal length of 12.0 cm. Dear Sir/Madam, The numerical values in the solution above were rounded when written down, yet un-rounded numbers were used in all calculations. The reflectance is a ratio of radiant flux. I would like to ask if you have information on how the protected silver mirrors(especially You currently have javascript disabled. How can CRDS be used to determine the reflectivity of an unknown test mirror when the total loss measured includes losses from both the unknown mirror and the other mirror making up the resonant cavity. If you have a camera which is sufficiently consistent in exposure time, so that the same scene from picture to picture has a variance (outside of pixel-count noise) of no larger than a percent or two, you're equipped. Please note that we have a buffer built in between the specified damage thresholds online and the tests which we have done, which accommodates variation between batches.
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