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Scanning-Slit Optical Beam Profilers![]()
BP209-VIS Post and Post Holder
Application Idea For a complete beam quality measurement system, integrate a beam profiler with an M2 measurement extension set. (Shown: BP209-IR and M2MS) ![]() Please Wait
![]() Click to Enlarge One Possible Configuration of the Beam Software GUI Showing Reconstructed 2D View, Calculation Results, Plot Position vs. Time, X Profile, and Pseudo 3D View Windows Enabled
Features
Software Features
Thorlabs' Dual Scanning Slit Beam Profilers are ideal for analyzing cross sectional profiles of near-Gaussian laser beams. Measurements of the intensity profiles along the user-specified X and Y axes of the beam's cross section are acquired at scan rates between 2 Hz and 20 Hz, which can be set using the software. The fast 20 Hz scan rate enables real-time optical system alignment. Primarily intended for CW laser beams, >10 Hz pulsed beams can also be measured using an averaging technique (see the Operation tab for more information). These measurements can be used for beam quality evaluation, examination of the reconstructed beam profile, and monitoring long-term stability. These scanning slit beam profilers are equipped with low-noise electronics, have a high dynamic range of 78 dB, and are capable of measuring beams with diameters between 2.5 µm and 9 mm. The beam diameter is measured in accordance with the ISO 11146 standard and can be displayed using a number of industry-standard clip levels, such as 1/e2 (13.5%), 50%, or an arbitrary clip level set by the user. When the beam of interest does not have a near-Gaussian beam shape, or when single-shot measurements of pulsed beams are required, we recommend our CCD Camera Beam Profilers. There are three Dual Scanning Slit Beam Profiler models available. The BP209-VIS(/M) is for use over the 200 nm - 1100 nm wavelength range, the BP209-IR(/M) operates over the 900 nm - 1700 nm range, and BP209-IR2(/M) has an extended near-IR wavelength range of 900 nm - 2700 nm. All models have a Ø9 mm physical input aperture and make measurements by sequentially scanning two slits with the same width and orthogonal orientations across the input laser beam. Use the software to switch between pairs of 5 µm or 25 µm width slits, select scanning-slit or knife-edge mode operation, and set a range of scan options. For information about the functionality and the usage of the different slit widths and operating modes, please see the Operation tab. Thorlabs' Beam software offers complete control over the operation of these beam profilers, providing a broad range of user-adjustable settings as well as display and data logging options. The software and can be downloaded from the Software tab and installed on a user-supplied PC. When the beam profiler is connected to a PC running the Beam software, no additional hardware or power supply is required. Thorlabs utilizes a high-speed USB 2.0 interface to connect the measurement head with the PC, and the required USB cable is included with the BP209 package. Flexible data export options as well as a data interface for National Instruments® software ease the integration of these profilers into customized data processing environments. Please see the User Interface tab above for more details on the functionality of the software. M2 Measurement Systems
All technical data are valid at 23 °C ± 5 °C and 45 ± 15% relative humidity.
Slit and Photodiode PositionAccurate measurements require a ≤Ø9 mm beam to be centered in the entrance aperture, the slits to scan the entire beam, and all transmitted power to be incident on the photosensitive surface of the photodetector. Please consult the drawing for the BP209 model of interest, shown below and included in the manuals, for information about the distances separating the front face of the entrance aperture, the slit location, and the position of the photosensitive surface of the photodiode. These dimensions are provided to help the user ensure that the optical input, especially in the case of a highly diverent beam, is not clipped by the entrance pupil and does not overfill the photosensitive surface of the photodetector. Scanning-Slits and Knife-Edge TechniquesThe BP209 series of Slit Beam Profilers analyze near-Gaussian, elliptical (or circular) free-space optical beams using either the scanning-slits or the knife-edge technique, depending on the diameter of the beam. These approaches scan two slits, one after the other, across the full cross section of the beam. One slit is scanned along the X axis of the beam, and the other slit is scanned along the Y axis, where the X and Y axes are defined by the user and frequently correspond to the major and minor axes of the ellipse. The light transmitted by the slit is incident on a photodetector. Optical intensity measurements, which are referenced to the position of the slit, are acquired as the slit scans across the beam. The scanning-slit mode is appropriate for beams whose diameters are at least four times the width of the slits. In this mode, when the beam overlaps with the slit, a sliver of the beam with a width equal to that of the slit is transmitted. As the slit scans across the beam, the optical intensity of the sampled beam segments is measured by the photodetector. Knife-edge mode should be used when the beam diameter is smaller than the slit width. In knife-edge mode, the scanning slit transmits fractions of the beam, from zero to 100%. The scanning slit first overlaps with and transmits little of, then more of, and eventually all of the beam. The amount of overlap between the slit and the beam, and therefore the transmitted optical intensity, decreases and becomes zero again as the slit continues to scan across the beam. These measurements are used to determine the beam intensity profiles along the X and Y axes of the beam. Using these data, peak power and beam centroid locations with respect to each axis are found, as well as beam diameter and ellipticity. By assuming the beam has a near-Gaussian profile, the measured X and Y beam profiles can also be used to reconstruct the intensity profile of the full beam cross section and plot the results in either 2D or 3D formats. ![]() Click to Enlarge Operate in Knife-Edge Mode when the beam diameter is less than the slit width, as shown above. Choose Scanning-Slit Mode when the beam diameter is at least four times greater than the slit width. ![]() Internal to the BP209 series measurement heads is a rotating drum, whose axis of rotation is adjusted using a manual knob. Slits in the drum are scanned across the X and the Y axes of the beam as the drum rotates, and transmitted intensity is detected by an integrated photodetector. Operational Overview of the BP209 Series Beam Profilers
Thorlabs' Beam Software
![]() Click to Enlarge The laser-engravings on the front face show the orientation of the X and Y axes when the knob is vertical and can be used to estimate the axes' orientation when the knob is rotated. Perform Measurements with 5 µm or 25 µm Slits If the beam diameter is equal to or less than 20 µm, use the 25 µm slits and operate in Knife-Edge mode. Beams with diameters as small as 2.5 µm can be measured using this approach. The Scanning-Slit mode can be used to measure beams with diameters between 20 µm and 9 mm. As a general rule, choose slits with widths at least four times smaller than the beam diameter to make the measurement. When this condition is met by both slit widths, the choice of scanning slit pair is influenced by the beam power and application requirements. Measure Beams with a Wide Range of Powers As discussed below, reduced maximum and/or increased minimum beam power limits may apply when the beam profiler is used to measure total power (see below). If the Total Power measurement falls outside of the applicable limits, an error message will be displayed in the status box. However, beam shape measurements using the slits can still be made, assuming the power transmitted by the slits falls within the limits plotted in the diagram. Acquire Total Power Measurements (Power Meter Readings) The ranges of maximum and minimum beam powers for which Total Power measurements can be acquired may not reach the limits plotted above. The limits in the graph were determined for knife-edge and scanning-slit mode operation. Scanning-slit mode transmits a fraction of the beam power to the photodetector, and during knife-edge mode the un-attenuated, ≤Ø20 µm, full beam is transmitted to the photodetector. The power in the attenuated full beam that reaches the photodetector during Total Power measurements may need to fall within reduced maximum and/or increased minimum limits than the beam powers accommodated when operating with the slits. Choose the X and Y Scan Axes' Orientation This functionality is of particular importance when the input beam has an elliptical cross section, as the scan axes must be aligned with the major and minor axes of a given beam in order to measure the real ellipticity. To achieve the most accurate alignment for an ellipticity measurement, rotate the knob while observing the X and Y intensity profiles plotted in the software. When the profile width in one axis is a minimum and the other is a maximum, the rotation angle is optimum. Measure the Beam Profile of Pulsed Laser Beams There is no difference between analyzing a CW signal and a pulsed signal when the pulse repetition rate is high and the duration is short, as is the case with a femtosecond laser with 100 MHz repetition rates and pulse durations lower than 100 fs. This is due to the limited bandwidth of the photodiode’s current amplifier, which cannot resolve the individual pulses and instead effectively averages the input pulse train to produce a CW signal. When pulse rates are lower, on the order of 50 kHz and less, configure the Scan Rate setting in the software to achieve optimal measurements. As the scan rate can be set between 1.5 Hz and 20 Hz, it is frequently not possible to set the scan rate to be as fast as the pulse rate. Set the scan rate so that an integer multiple of the scan rate is slightly different than the pulse rate. Then, perform the measurement with the Hold Maximum function enabled. A set of scans are performed, and the software accumulates and averages the measured peak intensities in the scan set. When the pulse rate is fast enough for more than one pulse to be measured during a single scan, the software will accumulate and average the peak intensities of all the measured pulse segments. The reported beam profile is the final average of the set of measurements. Setting the integer multiple of the scan rate to differ slightly from the pulse rate ensures that each scan measures a different portion of the beam profile; the set of scans should include measurements of all segments of the beam profile. Main Window![]() Click to Enlarge The main window of the GUI includes the menu bar, tool bar, status bar, and a frame where several windows can be displayed. This version of the Main Window includes several panels: Beam Settings, Calculation Results, 2D Reconstruction, and 3D Profile. The Beam Settings Panel displays all important information in a single location; this panel can be unpinned from the main window and moved to a second location, such as another monitor. Thorlabs Beam Software for the BP209 Beam Profilers
Thorlabs' Scanning Slit Beam Profilers, Camera Beam Profilers, and M² Measurement Systems all use the Thorlabs Beam software package. The screenshots below highlight key features and measurement modes that can be used with our scanning slit beam profilers, including 2D reconstructions of the beam profile and measurements of the beam stability and position. If an M² Extension Set (available below) is added to the system, the software also enables M² and beam divergence measurements. 2D Reconstruction of the Beam Profile![]() Click to Enlarge Slit beam profilers only measure two real orthogonal cross sections of the beam (i.e., the beam profile in X and Y). Assuming a Gaussian-like beam profile, the Beam software package can create a 2D reconstruction of the beam profile from the two cross sections, seen in the screenshot above. Buttons along the side allow users to save the image, show or hide the x and y scales, mark the centroid or peak position, and display an approximated Beam Ellipse superimposed on the image. Calculation ResultsThe Calculation Results window (left) displays the results of calculations performed by the software, including beam width, centroid and peak positions, power, ellipticity, and fits of the beam profile. This panel also includes a Pass/Fail test. For each parameter, a minimum or maximum can be set as criteria. After the calculations are complete, the user can save them in .txt, csv, or .xls format (screenshot to the right). In addition to saving single measurement results, diagrams, and device data, the software can automatically sequentially save this information for a series of measurements.
Beam Stability![]() Click to Enlarge The Beam Stability Window allows the stability versus time to be recorded and viewed. Display options include the Centroid Positions, Latest Plotted Centroid, Rolling Centroid Positions, Reference Positions, and Smallest Enclosing Circle. Plot Centroid and Peak Positions![]() Click to Enlarge The positions of the X and Y peak and X and Y centroid positions can be displayed as a function of time in this window. M2 Measurements![]() Click to Enlarge The beam diameter and location of the beam waist are shown after an M² analysis has been performed. Note: This functionality is only enabled when one of the M² analysis systems is connected to the PC. Convergence / Divergence Measurements![]() Click to Enlarge The divergence of the beam is shown after an M² analysis has been performed. Note: This functionality is only enabled when one of the M² analysis systems is connected to the PC. Software Packages for Thorlabs' Beam ProfilersThe Beam software package can be downloaded by clicking on the Software button below. The software download page also offers programming reference notes for interfacing with our beam profilers using LabVIEW™, Visual C++, Visual C#, and Visual Basic. Please see the Programming Reference tab on the software download page for more information and download links.
Features
SoftwareVersion 7.0.4133.305 (November 14, 2017) Standard full version of software package for 32-bit and 64-bit Windows with driver and graphical user interface for operating the device in standard applications. Firmware Update for Scanning Slit Beam ProfilersBelow is a link to a firmware update for Thorlabs scanning slit beam profilers to correct an error regarding hardware and firmware compatibility. Each Beam Profiler Comes with the Following Parts:
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These extension sets are designed to convert Thorlabs' Camera or Scanning Slit Beam Profilers into a fully automated, motorized M² measurement system. The M2MS has internal mirrors for wavelengths between 400 - 2700 nm and the The beam profiler and focusing lens remain in a fixed position. For M2 measurements, the beam path length is varied using a movable retroreflector mounted on a previous-generation DDSM100/M translation stage, which has a translation range of 200 mm and a maximum velocity of 500 mm/s. The side of the M² measurement system features an integrated USB 2.0 hub, which has ports for the beam profiler, one other device such as the TSP01 USB temperature and humidity controller, and a mini USB output connection to a PC. The translation stage inside of the system also communicates with the computer through this hub. The system is controlled via the Thorlabs Beam software package, which is also use to control our beam profilers (see the Software tab), which enables accurate measurements of a variety of beam-related parameters. The housing of the M2 measurement rests on four feet at the corners created by a 0.5 mm deep relief cut in the base. A set of RDF1 rubber damping feet are included. Five M6 taps allow for the installion of four damping feet with one near each corner or in a configuration using three damping feet. More information about these complete M² measurement systems, as well information about M2 measurement systems that incorporate our CCD camera beam profilers can be found here. Lenses Included with M2MS-AL*Lenses with f = 250 mm Mounted in CXY1QF Quick Release Plate: *Additional lenses for shorter UV wavelengths and the CXY1QF quick release front plate are available separately to enable further customization of the M2 measurement system. Lenses Included with M2MS*Lenses with f = 250 mm Mounted in CXY1QF Quick Release Plate:
*Additional lenses for longer IR wavelengths and the CXY1QF quick release front plate are available separately to enable further customization of the M2 measurement system. Accessories Included with M2MS-AL and M2MS
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