- Photodiode-based sensors, used for measuring low powers (from pW up to several hundred mW, typically); these are limited to spectral regions from the UV to the near IR, depending on the specific semiconductor used, and
- Thermal sensors, used for measuring higher powers; the most sensitive thermal sensors can measure from as low as tens of microwatts, and up to 100 KW and beyond.
Modern laser applications demand ever-increasing accuracy in the measurement and control of the laser beam. Various types of sensors and instruments are in use today, the choice depending on the type of measurement needed.
However, even given the correct choice of equipment, there are measurement conditions that can seriously affect the accuracy of the readings obtained if not correctly taken into account. Examples...
By Dan Ford Southwest Regional Sales Engineer, Ophir Photonics Group
In this application, our customer manufactures encoders that incorporate LED’s (light emitting diodes) that have a collimating lens attached. The LED’s produce between 850nm and 880nm at 2mW to 15mW, the beam sizes range from ¼” to ½”. Until now, a laser power meter has been used to verify the output wattage. Shining the beam on graph paper has been used to verify the beam size visually.
193nm excimer laser radiation needs special precautions in measurement because of its strong interaction with ordinary matter. This radiation is absorbed by ordinary air and water vapor in the air so that the intensity measured can vary by 1% per cm.
Instead of measuring power we measure total energy and the meter is fast enough to read out the energy and be ready for the next pulse 2.3s later. The accuracy of this method is better than +/-1%
When using a Fiber Adapter accessory together with one of Ophir's sensors, it is important to be aware of the power/energy density that is going to reach the sensor's surface.In most cases, the fiber adapter locates the fiber tip far enough away from the absorber surface that the spot diameter on the surface will be large, and problems of damage avoided. However, that is not always a certainty! For example, when using a sensor from the PD300 series, especially with filter IN, this distance could be quite small. A power level that is within spec limits...
If, for example, you need to measure energy at various points along an optical setup in order to characterize each stage of your system, you can place a sensor at each location along the way and connect the sensors in parallel to, say, a multi-channel Pulsar, and log the data using the StarLab application. So long as you open all channels in a single window and log from that window, all the channels will be synchronized with the same zero point. Knowing that, you can rely on the time stamps to tell you which pulse in each channel corresponds to which pulse in...
What is the best way to measure the power of a laser that is, unfortunately, not stable, where the power is drifting upwards or downwards. I am making a measurement taking readings by hand and logging to computer?
The best way to measure in such a condition is to take statistics of a number of readings. In order for the sample to be truly random, you should a given intervals look at the reading and take it down as seen with no attempt to wait for it to stabilize or reach a "better" value.
Ophir pyroelectric sensors can measure energy at very low repetition rates, what is called “single shot” energy as well as at various repetition rates all the way up to the maximum in the specification for such sensors. There seems to be a misunderstanding among users that pyroelectric sensors cannot measure single shot energy. This probably comes about since thermal sensors can only measure at very low repetition rates (~0.2Hz), then it is assumed that the converse applies to pyroelectric sensors, i.e. that they only can only measure at faster...
The global medical industry incorporates thousands of lasers into its arsenal of treatment tools. Wavelengths from UV to Far-infrared are used for everything from Lasik eye surgery to cosmetic skin resurfacing. Visible wavelengths are used in dermatology and ophthalmology to target selective complementary color chromophores. Laser powers and energies are delivered through a wide range of fiber diameters, articulated arms, focusing handpieces, scanners, micromanipulators and more.
Use the lowest range that is larger than the pulse energy to be measured. For example, if you want to measure a 2.7 Joule pulse, use the 3 J range instead of the 30 J range. This will allow for maximum resolution (a 2.700 J reading versus a 2.70 J reading).
For most energy measurements, the default MEDIUM setting is appropriate. If taking...
An explanation of how we do this is provided below (A). In addition, a recent check of Ophir’s 5000W head by PTB in Germany shows excellent agreement between our calibration and their standards. The details of the correspondence between our sensor and their standard at powers up to 1400W is included here (B).
A. High Power Measurement Calibration Method and Estimated Accuracy of Models 5000W and 10K-W
- The app does not require “state-of-the-art” phones. It works perfectly OK with 3 year-old HTC Legend (that was not top of the line phone even when it was first announced) and it works well with our test phone which is defined mid-to-low range in today’s phone standards.
- The software does require android version of 2.3.3 and above. According to latest analysis they account for over 99% of current phones (based on Google analysis of phones accessing Google Play). Since version 2.3.3 was...
Note the settings on your meter and sensor before sending the units in for calibration. To simplify the reintegration of your Ophir measurement instruments back into your system, please record your settings and parameters before sending your devices in for calibration.
During the calibration process occasionally we change the settings on an instrument back to the default. This means that when you receive the equipment back it will likely not start up as you had it. The end-user will see a change in how the meter and/or sensor are behaving. The difference could be as simple as changing the Average function, so the readings now appear less stable.
The entire aperture senses power, so you can use the whole head. That said, a beam in the inner 50% of the surface area (about 70% of the diameter) is specified by Ophir to be uniform within +/-2%. The sensitivity around the edges might be a little less, but generally the sensitivity doesn’t vary by more than +/-2% over the entire aperture.
The Ophir sensors are provided with a 1.5m cable between the sensor and the smart head connector. When a longer length cable is needed it can be provided, as long as it is within operational limits. However it is not possible to add an extension to the cable, because that moves the smart head connector away from the meter or interface unit which can degrade the smart head functionality or disable it.
It is recommended that the sensor be put in a well-ventilated container instead of being put into a tool bag or in an area where other things can contact the sensor surface. The meters too should be put into a container so the screen is protected from objects that might contact and break the meter's screen.
We are often asked about the specified ranges of various ambient conditions (temperature, humidity, etc.) for Ophir instruments. In this article we will clarify the effects of these conditions on laser measurements, so you’ll be able to use your Ophir laser measurement instrument effectively.
Since power and energy sensors use absorption materials that are not spectrally flat, you always need select the correct laser wavelength on the meter or in the interface software in order to achieve the specified sensor measurement accuracy. Power and energy sensors are calibrated to produce accurate measurement throughout their spectral range, however since they do not detect the wavelength in use, this is one entry that must be manually selected by the operator in order to achieve the specified accuracy.
Each given range represents one level of gain of an internal amplifier. The electronics, as always, have a limited Dynamic Range. If the measured signal is too low, in other words near the bottom of the range, then it may be lost in the noise and the reading will be inaccurate and noisy. If it’s too high – there may be saturation issues. To give an instrument a usefully wide dynamic range, multiple scales or ranges are used. Switching from range to range can be automatic (“Autorange”), or manual. Autoranging simply starts automatically at the least sensitive range and works its way down the ranges, sampling the signal as it goes, till it finds a range at which the signal is properly detected. Note, by the way, that only in POWER mode is Autoranging available. If we are working in Single Shot Energy mode, there is no Autoranging – simply because when we are measuring a single pulse, the instrument has no opportunity to work its way down the ranges as in Power mode.