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Knowledge is power

Rob Coppinger on why power meters are an important part of any laser set-up

Whether cutting metal or plastic or providing soft tissue therapy with a laser, knowing the power and energy properties of the beam is all important for good results. Monitoring the laser’s performance at the workstation or remotely, continuously or daily, power meters have an important role to play in process control and quality assurance.

‘You need to know how much power you have, because in marking if you have too much you can damage what you are marking. In cutting, if you don’t have enough [power] you won’t get a good cut,’ explains Ophir’s Jimmy Green.

The methods of measurement – and more significantly, the software with which these measurements are interpreted and analysed – have developed a great deal in recent years.

One aspect has been the increase in availability of remote sensing, whereby data from the sensors is transmitted over a local network or the internet, removing the need to have a PC or other analysis device close at hand.

‘I see a lot of companies that want multiple sensors through one import port with remote wireless sensing,’ says Green. Another trend Green sees is the movement away from using lots of meters to direct computer interfaces for the power and energy sensors. ‘There are different configurations for that, sensors with built-in electronics, [sensors that] plug directly into a USB for a computer, but that is often only for one sensor. Ophir has Juno, a computer to sensor interface,’ says Green.

Green gives the medical sector as an example. Doctors need to know what the power density and energy levels of the laser are, so that when they are treating a patient, the right dosage is given. For this, monitoring sensors are embedded in the medical devices and there is routine measurement of the laser equipment’s power and energy densities. This monitoring could involve a computer interface. As well as direct computer interfaces, a lot of production technology does not use Windows software, because they use Programmable Logic Controllers (PLC).  These use RS232 connections instead, not USB.

‘Everyone thinks RS232 is dead, but for system integrators, RS232 is critical, because they don’t necessarily have a Windows computer that can drive the USB plug,’ says Coherent’s product manager for laser measurement products, Sean Bergman.

Because of this Coherent has put a lot of emphasis on its RS232 support. ‘We’ve put a lot of work into launching the product about a year or so ago and expanding that across many sensors,’ Bergman explains. This product involved the miniaturisation of the power meter technology into a connector that can be used with an RS232 interface. ‘We call that our Powermax RS line,’ says Bergman. The idea is that system integrators can connect their sensors with the RS232 connector through its cable. Through the RS232 connector a PLC can send host commands to the sensors, while the sensors’ signal conditioning is carried out inside that RS232 power meter cum connector. ‘We can connect that up to all our power sensors and it allows an integrator to say “we need a 10W sensor”. If they want to embed that in their system and with RS232, they can just plug it in.’ Bergman adds that there is also an energy version of this product called Energymax RS and the corresponding USB product is the Energymax USB.

Energy is more complicated to measure, because the output is a curve on which users have to measure the peak. It’s a task that needs equipment that can take measurements very fast. ‘You have to sample that curve really fast and get the baseline and the peak,’ says Bergman. He only knows of a few companies that make their own ‘peak detection’ boards outside of the main manufacturers of measurement equipment, such as Coherent.

‘For those working in the field, the Energymax USB is ideal, as they don’t have to carry the bulk of the meter. The meter [again] is right inside the connector. It also supports labs where they have a whole bunch of sensors and want to plug them into a hub,’ says Bergman.

Monitoring the meter’s output doesn’t even need a typical desktop computer often found in many factories or labs. ‘What is really new for us is an Android app,’ says Ophir’s Green. ‘It is an app that allows you to take any Android-based phone and turn it into a meter, connecting through Bluetooth with an [Ophir] Quasar.’

Green explains that as well as being able to monitor processes at some distance, the phone can connect to multiple Quasars, as each Quasar has its own identifying code.

The internet and the rising use of consumer technology devices is not lost on Gentec Electro-Optic’s research and development vice president Robert Provencher and sales and marketing vice president Claude Lachance. ‘With the advent of wireless systems, the iPhone and the iPad, people want to obtain their measurements from these [devices]. This is a very new development and we have to meet that demand.’ Lachance adds that customers want to send their data through the ‘internet as well’.

However, the remote technology that Green expects to do very well is non-contact measurement. ‘This will be disruptive with current sensor technology,’ he says. ‘Products that achieve sensing without interrupting the beam are on the horizon; it is probably one to two years away. Prototypes have already been built, and patents applied for.’

The advances in sensor technology now relate to coatings, according to Green. ‘Advances in [coatings] deposition technology, for the thermal and electronic components within the sensors we make, have improved their accuracy from 3-5 per cent down to 1-3 per cent,’ says Green. The pyroelectric sensors, in particular according to Green, have improved substantially due to ‘material advances’. Some of those material advances are in the deposition technology, while others are in the material processing for the crystals that are used in the pyroelectrics. ‘So the sensors that Ophir makes have become more robust and accurate, simply due to material and process changes,’ adds Green.

Sensors are also a focus at Gentec. Lachance says: ‘Before we were focusing on a round beam and there was a limit, but now with fibre and diode lasers, which can have a large special shape, we have developed new [sensor] technology.’

For Gentec, technology development across the board is needed, because of the expanding requirements of the customers. ‘Now we measure in the femtojoule [range]. This was not in demand in the past. For pulse width, we are now dealing with femtoseconds, which we were not dealing with a few years ago. We have to develop quite a few technologies and products,’ explains Lachance.

Robert Wells is technical director at Lasermet, which has the ADM-1000 power meter, and product evolution is very much on the agenda. ‘We spend a lot of time measuring optical radiation,’ he explains. ‘The idea for the ADM-1000 was to bridge the functionality, to get away with fewer [sensor] heads, and it works very well. All the calibration is in the head, so you can put any head on any meter. We can measure down to four microsecond pulse length, which I am fairly sure is unique.’

The ADM-1000 also stands apart, according to Wells, because it includes an oscilloscope. ‘It gives you a good idea of what is going on with your meter and with your laser without having a separate bit of kit,’ he says. ‘[The sensor head] needs to be calibrated according to wavelength. We calibrate our meters to 32 different wavelengths.’

Wells also points out that businesses need several different sensor heads, because if users are dealing with a high power laser it will ‘just burn a hole in the photodiode’ that is measuring the power output. Photodiodes are much quicker than thermal heads, which is the other main group of sensors, but they are limited in the amount of power. They can’t cope with lasers that are much above a Watt. That is when thermal heads are needed.

The power meter is adapting to the changing needs of the customer and the expanding uses for lasers. Whether it is coatings or beam sensing without interruption, further technical advances will ensure the business of laser power and energy measurement will deliver the performance data users need.