When working with a laser, you must consider many variables to ensure everything is working correctly. A laser is much more than the light it emits, and even that can vary significantly. For example, the power of the laser determines a lot in a system, and this power is not always stable. Read on to learn everything you need to understand about laser power stability.
What Is Laser Power Stability?
The first part of truly understanding the complexities of laser power stability involves breaking down exactly what that means. A laser’s power is often a critical variable in applications, as a change in power will change the measurements at the core of your laser application. Many applications are susceptible to changes in power, making laser power stability so critical.
Laser power is the optical emission of a laser diode, and when that emission is not stable, your system is flawed. Some sources of instability include:
- Poor laser construction
- Temperature instability
- Current instability
- Poor fiber-coupling
- Improper heatsinking
Any operation with a laser source has a comfortable range of stability, and when it goes out of this range, it can affect the quality of whatever it is a part of. Quality and consistency are essential in any industry, and the best way to achieve that is with a stable laser power output. For example, the magnitude of the return signal in laser material analysis determines the properties of the material, such as thickness or possible defects. Without a stable laser to deliver consistent light for such a measurement, inaccurate and misleading measurements can occur.
Similarly, if you’re in a field that uses lasers for remote gas sensing or space exploration, you must use accurate, stable instruments. As mentioned, an unstable instrument can completely derail your project with incorrect results.
The Consequences of Laser Power Instability
So, what are the different consequences of poor laser power stability? Whatever your project may be, you want things to work out well and accurately. Unfortunately, laser instability can get in the way of these results. Often, an unstable laser can make the difference between a helpful result and one that is ineffective. However, something worse than a blatantly bad result is one that you incorrectly think is good, leading you to the wrong conclusion.
People use lasers in many different applications, with many using them for their research purposes. One example of lasers’ practical application is in medicine, where they can help destroy kidney stones, aid in eye surgeries, or diagnose conditions such as cancer. In addition, research applications such as nuclear fusion, particle acceleration, and microscopy all rely on lasers. The stability and accuracy of those lasers are essential in ensuring the data and results are accurate.
Which Factors Determine Laser Power Stability?
But what are the factors determining the stability of a laser’s power? As mentioned previously, factors of the construction of the laser setup, such as the fiber-coupling and heatsink components, will affect stability, but there are also many outside factors. For example, because a laser is a high bandwidth device, poor power supply stability will directly translate into poor laser stability. This stability is noticeable in its short-term performance in the form of sub-second variations that can constitute “noise.” However, it also affects long-term performance over days, weeks, or even years.
Another critical factor is the temperature of the laser. Poor temperature control will affect the performance of the laser and can ultimately damage the internal optics and fiber coupling. This damage will lead to further and more significant issues as the integrity of the laser worsens over time. These internal components will also be affected by age, so the older your laser gets, the less stable its power output will be.
Ways To Monitor Laser Power Stability
Thankfully, there are ways to monitor the stability of your laser and measures you can take to fix any instability issues. There are a few different kinds of laser power monitors that you can have for your systems, such as continuous power detection monitors or full power monitors.
For full power measurements, you can use optical detectors to capture some of the laser power. These detectors are either silicon, germanium, or Indium gallium arsenide (InGaAs). You can also use integrating spheres for high-power applications along with semiconductor detectors. Thermopile-based detectors are a cost-effective solution for some, but these solutions may also be less accurate.
For continuous power measurements, internal monitor photodiodes can provide feedback, but the quality of this feedback all depends on the laser’s design. For example, tap couplers work for fiber-coupled lasers, beam splitters work for free space lasers, and each split off a small percentage of the laser’s power for powering the optical detector.
Ways To Fix Stability
You can also improve your laser’s stability by eliminating some outside factors and taking care of more internal ones. One significant way to make your laser system more stable is by allowing the instruments time to warm up before use. Many of the internal components of your laser setup, such as resistors and capacitors, change along with the temperature. To obtain accurate results and have your setup be more stable, you should allow your instruments to stabilize thermally.
There is quite a measurable difference in the power of a laser the moment you turn it on versus several minutes later. Most manufacturers provide recommendations for power on measurement and control electronics for one hour; refer to these guidelines for the most accurate performance. Another way to make your setup more stable is to always use the laser in the same environmental conditions. Do your best to keep everything the same, including ambient temperature, cooling mechanisms, laser wavelength, power levels, and warm-up time.
Another way to ensure your system is more stable is by using a quality laser driver. Power fluctuations won’t drastically affect the laser’s output with a good driver. Similarly, invest in a quality temperature controller capable of good temperature stability. For example, a high-quality heat sink that properly mounts the device will ensure that heat generated from laser use will not influence its overall performance.
There’s a lot you need to understand about laser power stability, and you must have the optimal setup to maintain this power. Unstable laser power can result in poor or incorrect results that lead you to the wrong conclusion. Thankfully, devices such as laser diode drivers can help keep the laser’s power stable. At Arroyo Instruments, we have all the drivers and any other equipment that you may need for your specific laser setups.