We recently came across an interesting customer problem, in which every time he disconnected the FO connector from the adapter (that is mounted on the sensor) and then reconnected it, the power read about 50-100 uW higher than it did (nothing else changed). It then took about 10 minutes to slowly come back down to what it had been. After an investigation, we found that the increase in reading when disconnecting/reconnecting the fiber connector is a thermal effect, and not a technical flaw in the unit. If you experience something like this, the most likely direct cause is one of the following 2 possibilities:
- As the FO connector is disconnected from the adapter (that is mounted on the sensor), and the connector is moved away from the sensor, for a brief moment the beam is incident on the body of the adapter itself; that adapter is black metal, and the heat created in it by absorbing a beam of 1mW for a second or two might be very small – but it could, possibly, be enough to be detected by the sensor. It also seems reasonable that it would take quite some time for this heat to dissipate and the reading to come back down to the correct level, since there is very little thermal contact area between the adapter and the sensor body.
- It could also be that the heat from the hand unscrewing the connector could have the same effect as above. (As an experiment, you can try touching the body of the 3A sensor itself – the reading will go up, and then down again. That will happen much faster than the above problem, since a touch right to the sensor’s body will cause a much more immediate heat flow than touching the adapter out at the end of the tube).
TThe best way to solve/avoid this problem is to try disconnecting/ reconnecting the fiber (when you need to do so) at some location than the fiber adapter on the sensor (either at the laser end, or any other connections along the way between the laser and the sensor if there are any). That way there is no heating of anything near the sensor (and no artifacts that could be caused by turning the laser itself off and on).
If you have a measurement setup with a beam splitter or attenuator the Attenuate Function in a Nova II or Vega can be used to measure the laser power or energy before the splitter or attenuator. For example, if you are splitting off 10% of a laser beam into the sensor and you wish to display the full beam, do as follows:
- From the main power or energy measurement screen, enter menu, select “Attenuate” and enter again.
- Enter “Beam %” and then with the up/down navigation buttons, select the first number. With the right navigation button go to the second number, and with the up/down navigation buttons select the second number and so on. For example, in the screen shown below in Figure 1, the selection is 10%.
The large number shows the full beam power/energy impinging on the beam splitter and the small number is the power/energy actually measured by the meter.
For scanning low-level beams, such as bar code scanners, the Ophir special photodiode sensor model BC20 is the recommended choice. With scanning or moving beams the PD300 sensor, which is intended for stationary beam measurement, will not work properly. The key feature of the BC20 is the peak hold capability that the PD300 does not offer. Below is a simplified diagram of the BC20 circuitry that provides this unique scanning beam measurement capability.
The Laserstar has an exclusive audio tune capability within the Power Tune function that makes adjusting your laser to its maximum power easy. Unlike a bar graph or mechanical meter, the Power Tune screen graphically shows what came before as well as the current reading and the trend. This allows you to determine if you have reached maximum power. The screen is completely auto-ranging. Therefore, as soon as the cursor goes over the top or under the bottom edge of the display, it re-scales to put the cursor back to the middle of the screen. This allows you to devote all your attention to tuning the laser, without having to worry about the Laserstar settings. The Laserstar can generate a rising or falling audio tone to indicate higher or lower power. You can also use the audio tone feature so you do not have to look at the LaserStar at all while tuning the laser.
To use the LaserStar to fine-tune laser power:
- From the main power measurement screen press the menu button then select "tune". Now press "go" then "setup".
- Set the percentage range of the power scale to be displayed by repeatedly pressing the value key.
- Now select the horizontal sweep time you desire. Now select if you want an audio tone for tuning or not.
- Now press "exit" and use the Power Tune screen to tune the laser power.
When measuring the energy of a pulsed laser setup with a pyroelectric energy sensor for the first time or after changing a setup, use the pyroelectric damage test slide provided with the sensor to insure the new energy and fluence level will not damage the sensor. The damage test slide is made of the same material as the sensor absorber and coated (if appropriate) with the same damage resistant coating. If you don’t have a damage test plate, or would like extra slides, you can contact firstname.lastname@example.org or email@example.com to order the appropriate damage test slide for your sensor.
Open StarLab and click on File and Open. Select the log file you want to open and click Open. This will load the log file into StarLab. Now to zoom in to a specific section click and hold on the area to the left side of the area you want to zoom in on. Drag the mouse curser to the right as far as you want the section to zoom in on and release the mouse button. You can continue to zoom in in this same way. If you need to zoom out, click and hold anywhere in the zoomed in area and drag to the left and release. It will zoom all the way out.
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.
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.
The online sensor finder now gives comments to help the user find a solution in case he does not succeed in doing so. Examples below:
For optimal accuracy the Ophir thermal power meter sensor will be placed in the beam path perpendicular to the incident beam. There is an angular dependence that will reduce the measurement accuracy by some percentage as is indicated in the chart below. It is recommended that the angularity not exceed 20-30 degrees in order to keep the error to an acceptable minimum.
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.
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.
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.
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.
For certain pyro sensors with a diffuser, such as the PE50BF-DIF-C P/N 7Z02941, there is a Note (b) that for 10mm beam size the damage threshold specification should be derated by 50%. To explain why the damage specification is derated for a larger beam size, please see the picture illustration below. This has to do with the smaller relative increase in spot size lowering the energy density less on a larger beam than the larger relative increase in spot size with a smaller beam lowering the energy density more.
In order for LabVIEW to work with an Ophir power meter or PC interface, you must install StarLab. LabVIEW does not communicate via the StarLab application. We created a special COM object control for integration intent. You do need to Install StarLab in order to communicate with the device. The installation process of StarLab also installs the necessary USB drivers and registers the OphirLMMeasurement COM object required for LabVIEW (or other user programs) for communication with Ophir power meters and PC interfaces.
If you do not wish to install StarLab on your LabVIEW PC, there is a way. The document available at;OphirLMMeasurement_COM_Object.pdf
describes Ophir's COM object, including how to do it without installing StarLab.
An integrating sphere is used to measure a divergent light source. As shown in the illustration, an integrating sphere has its inner surface coated with a surface that highly reflects (typically 99%) in a scattering, nonspecular way. Thus when a divergent beam hits the walls of the integrating sphere, the light is reflected and scattered many times until the light hitting any place on the walls of the sphere has the same intensity.
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.
We try to note the settings and return them to the as-received state, but this isn’t always possible.
Note your settings. It might prevent a call to Customer Service and hours of frustration.
- For measuring Power:
- Average – On or off. If Average is on, note the time –i.e. 3 sec, 10 sec, etc.
- For measuring Energy:
- Threshold – For thermal sensors, Low, Med, High.
- For pyroelectric sensors, note the pulse width setting. The new pyroelectric sensors have many other options, such as threshold settings for noisy environments.
While we try to leave your instrument settings as they arrive, this isn’t always the case. Taking a few minutes to note the settings before you send your equipment in for calibration will save time when you reintegrate the devices into your measurement system.
A laser power sensor absorbs laser power while measuring it. If that power is not removed at least as fast as it comes in, the sensor could overheat and fail.
Many of Ophir’s OEM power sensors have a maximum average power specification of “XX watts free standing, YY watts heat sinked.” How does one make sure that a sensor has been provided with proper heat sinking? While we do not provide heat sinks, we do offer some guidelines.
We need to consider two separate issues:
- Conduction of heat out of the sensor into the heat sink
- Dissipation of the heat from the heat sink to the air
Ophir power meters use a 12 VDC power supply that supplies 500 mA. This power supply is reverse voltage to most US products, meaning the outside connection is positive (+) and the inside is negative (-). When connecting a power supply to the Ophir power meter, make sure that the power supply is a 12 VDC 500 mA power supply and that the center is positive (+). Some of the newer Ophir power meters like the Vega and Quasar are dual voltage compatible meaning it does not matter if the power supply is center positive or center negative. It still needs to be 12 VDC and 500 mA, but it can be either a center positive or center negative. It is highly recommended that the original power supply included with the equipment be used and if it is missing that Ophir be contacted for a replacement supply.
- The application 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 65% of current phones (this information comes from google analysis of active phones). Since version 2.3.3 was released in early 2011, almost no new phones are sold with older versions. The contract commitment in the US is usually two years, so most 2.2 and 2.1 phone owners there will probably upgrade to newer phones in the coming months.
To download the Quasar Reader App
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
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 measurements in a noisy environment or where there is a high level of background thermal radiation, the instrument may trigger spuriously on the noise or the background radiation. In this case, the user may select the HIGH threshold setting. This will prevent false triggering and ensure the sensor is measuring the intended pulse. If you are measuring small energies and the unit does not trigger, set the threshold for LOW. LOW threshold may also be used for the best accuracy if the energy measured is less than 10% of the range. For example if measuring less than .3 J in the 3 J range, LOW threshold is often more accurate, and will be more repeatable.
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. With all these variables, medical laser service personnel are faced with multiple measurement obstacles. At the Laser Training Institute (lasertraining.org), with headquarters in Columbus Ohio, we offer a week-long laser service school to medical service personnel. Four times a year, a new class will learn the fundamental concepts of power and energy densities, absorption, optics and most of all how lasers work. With a nice sampling of all the major types of medical lasers, the students learn hands-on calibration, alignment and multiple service skills.
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 repetition rates, but this is not true.
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.
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 the other channels.
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 could still result in a power density on the filter that is too high, and the result could be damage to the filter. In most cases, as noted, this is not a concern, but in cases where any one parameter seems like it is going to be near a limit, a quick sanity check is a good idea.
The high power sensors work on the thermopile principle, where the heat flows radially in the absorber disk causing a temperature difference between the hot and cold junctions of the thermopile which in turn causes a voltage difference across the thermopile.