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.
- Challenge: ever increasing demand for more accurate measurement
- Solution: constant improvements in equipment and methods
- How do we calibrate laser Power / Energy?
- Basic method: stable laser and substitution
- What is expected accuracy in simple case?
(power cal and wavelength available at NIST)
The Quasar wireless Bluetooth laser power and energy measurement interface allows quick and trouble free installation of complex measurement systems in an existing manufacturing environment, with a minimum of cable laying and disturbance to the facility’s operations.
This was demonstrated in a project undertaken recently, and is a typical example of what of multi-user systems see in the field.
Calibration is perhaps the most important of our products. We have a complete line of calibration lasers so that we can always calibrate at or near the customer’s wavelength. These lasers include powers up to 400W and both CW and pulsed lasers. In addition, we have a number of heads calibrated at NIST used as calibration standards. Below is a list of the calibration wavelengths used at Ophir in calibrating our standard catalog heads. Usually the calibration is done at representative wavelengths within a band of wavelengths where the head is spectrally flat. The calibration then applies to any wavelength in this band. The specifications note the maximum additional error in each wavelength band due to variations incalibration between the wavelength of calibration and the wavelength of measurement.
One of the inconveniences in the measurement of laser power and energy is what to do with the cables connecting the display to the sensor. These cables are of a limited flexibility and they clutter the workspace where the measurement is to be done. Sometimes, due to their stiffness, a motion of the cable moves the sensors and misaligns the set up.
Ophir Photodiode sensors use silicon, germanium and InGaAs sensors together with built in and removable filters. The spectral response of these type of sensors vary widely with wavelength. When used with our smart displays or PC interfaces, the sensitivity factor for the relevant wavelength is automatically set when the user inputs the laser wavelength.
The need to accurately measure laser power and energy has increased as more of these systems are used in medical procedures and industrial processes. Although a fairly simple process, this measurement is not as straightforward as an electric power measurement. With lasers, more attention must be paid to the selection of the right sensor as since different sensors perform different measurements. Selecting the wrong sensor can destroy the laser.
From the time of its invention, more than 30 years ago, the laser power meter was generally comprised of two parts: a measurement head and a display box. It was always considered better to have such an arrangement with a cable connecting the two because of the hazardous nature of the laser beam. As the display of the results is separated from the measurement head, so are the eyes of the operator separated from the laser beam.
Now that the PC is an indispensable part of the office and the laboratory, it is important to be able to integrate measurement instruments to the PC, particularly instruments that can gather large volumes of data. There is a need for a unified connectivity architecture wherein all measurement heads are compatible with all display boxes and are then easily connected to the PC.
Careful measurements are considered when testing the optical power, current, voltage, wavelength, and temperature of high output laser diodes. The test system energizes and measures the laser parameters as it will be used in the application. In some critical constant wave (CW) applications, the required output power from the laser is pushing the laser’s maximum specifications. Therefore, an accurate, stable, low drift laser power meter is required.
This document was created to assist our valued customers in the proper care and maintenance of Ophir-Spiricon pyroelectric laser power sensors. The following information is for reference only. If you have any reason to believe that the sensor is no longer performing within the original specifications, we always recommend that you send it in for repair and/or recalibration by our trained technicians to bring the unit back to the proper NIST traceable standards.
We believe that Ophir pyroelectric sensors can be used for many years without repair...
The Renowned German standards laboratory Physikalisch-‐Technische Bundesanstalt – PTB, has now developed a highly accurate calibration standard for calibrating Terahertz radiation based on a modified Ophir 3A-‐P meter.
The laser industry is advancing steadily with new wavelengths, higher powers and energies, and new applications all the time. As the power, energy and variety of new lasers advances, so measurement of these lasers has to advance.
As described in the general introduction, the thermopile sensor has a series of bimetallic junctions. A temperature difference between any two junctions causes a voltage to be formed between the two junctions. Since the junctions are in series and the «hot» junctions are always on the inner, hotter side, and the «cold» junctions are on the outer, cooler side, radial heat flow on the disc causes a voltage proportional to the power input. Laser power impinges on the center of the thermopile sensor disk (on the reverse side of the thermopile), flows radially and is cooled on the periphery. The array of thermocouples measures the temperature gradient, which is proportional to the incident or absorbed power. In principle, the reading is not dependent on the ambient temperature since only the temperature difference affects the voltage generated and the voltage difference depends only on the heat flow, not on the ambient temperature.
Ophir has two types of energy sensors, pyroelectric and RP. Pyroelectric sensors are for measuring repetitive pulse energies and average powers at pulse rates up to 25000 pulses per second and pulse widths up to 20ms. RP sensors are specialty items mainly for very long pulse widths and very high average powers that cannot be measured by pyroelectric sensors. Note that single shot energy with pulse rates less than one pulse every 5s or so can be measured with thermal sensors described in the power sensor section
A common thread running through many Frequently Asked Questions relates to damage of measuring sensors.
Many applications involve considerable powers and/or energies; since laser measurement has us deliberately putting a measuring instrument in harm's way, let's have a look at the various effects a laser beam can have on an instrument in its path.
We have included this document with your recent calibration order because we have noticed an out of tolerance condition obtained from your equipment when returned for calibration. This document was created to assist our valued customers in the proper care and maintenance of Ophir photodiode sensors. The following information is for reference only. If you have any reason to believe that the sensor is no longer performing within the original specifications, we always recommend that you send it in for repair and/or recalibration by our trained technicians to bring the unit back to the proper NIST traceable standards.
Ophir photodiode sensors can be used for many years without any repairs when used with the proper laser optical setup. Many of our customers have sensors that are using their original absorber that are over ten years of age. We hope that this document will enable you to also enjoy the long life and reliable results that Ophir- Spiricon is known for.
Most drivers get caught speeding at some time during their driving experience. A common scenario occurs when a policeman uses a LIDAR speed meter to indicate that a car is over the speed limit. When the car is caught and pulled over, the driver shows a surprised, innocent face, attempting to get out of a fine. But when the policeman shows the driver the reading on his LIDAR speed meter he knows he’s going to have to pay. Can the driver claim that he was within the speed limit, claiming that the LIDAR instrument is not calibrated recently?
Various LIDAR instruments may be used to measure speed, direction of motion of a motor vehicle, and the distance to another moving vehicle. LIDAR instruments are used by the police to enforce speed limits and to analyze car crashes or crime scenes in order to reconstruct the scenes.
PREH, Saale Germany, manufactures electronic controls for some of today’s finest automobiles. Production facilities are located in Portugal, Mexico, Romania, and the USA. PREH uses laser ablation technology to manufacture the controls that operate climate and driver systems. This process is made possible when a focused laser beam is used to remove layers of coatings to form an optically transmissive area of the device. This transmissive, laser etched area forms the symbol that informs the driver of the controls function.
Power and Single Shot Energy Sensors
Ophir provides two types of power sensors: Photodiode sensors and Thermal sensors. Photodiode sensors are used for low powers from picowatts up to hundreds of milliwatts and as high as 3W. Thermal sensors are for use from fractions of a milliwatt up to thousands of watts.
Thermal sensors can also measure single shot energy at pulse rates not exceeding one pulse every ~5s.
Repetitive Pulse Energy Sensors
For higher pulse rates, Ophir has pyroelectric energy sensors able to measure pulse rates up to tens of KHz. These are described in the energy sensor section, section 1.3.
The assessment of laser beam exposure used for entertainment applications is a challenging undertaking; both the emission and the environment pose particular obstacles to persons with the responsibility of ensuring emissions are below the permissible exposure limits. This article discusses how use of Ophir’s BC20 detector is able to offer significant improvements in measurements quality over traditional laser power detectors intended for CW beams. In addition, the BC20 simplifies the measurement process and allows measurement of live effects, opening the way for assessments to be undertaken with a much greater degree of accuracy. This provides benefits to assessors, whether they are operators, venue safety staff, or regulators, who can now additionally monitor emissions and ensure they are not exceeded during performances.