Optical parametric oscillator (OPO) lasers test optical fibers and components to characterize the spectral response of optical components, which can provide a competitive advantage in the optics industry.
OPO lasers have long been used in sophisticated test and measurement applications such as mass spectrometry, photoacoustic imaging and spectroscopy. Now, these “tunable” pulsed lasers are being utilized to facilitate a range of tests at different wavelengths to qualify and quantify the performance of optical components such as fiber optic strands, filters, lenses and coated mirrors.
By design, most optical components reflect, filter or transmit specific wavelengths, or ranges of wavelength. Therefore, it is critical to perform tests of component materials and coatings to ensure products perform as expected. The more precise these tests, the higher the product quality—a factor manufacturers can turn into a competitive advantage.
Because testing conditions should replicate or simulate the actual operational environment, lasers can be used to deliver a narrow wavelength band, pulse duration (if applicable) and power level to determine the spectral response of optical components.
These tests deliver critical information to optical component manufacturers related to factors such as absorption, scattering and other optical properties. Damage testing has become essential to identify if given optical materials can be damaged at different wavelengths. Coatings can also become compromised at specific wavelengths, causing performance issues.
Because there is such a range of tests, there is an advantage if the laser can be tuned to any required wavelength. This allows more flexibility and decreases complexity so manufacturers can ensure optical products perform as expected.
There can be significant benefits in using pulse-based lasers. Although continuous wavelength lasers are an inexpensive solution for testing optical materials, they do not provide a broad range of high-resolution wavelengths, and the peak power they can generate is limited.
Pulse-based lasers produce high intensity light bursts that can be used to determine if the transmission properties of optical materials or coatings are affected. Optical component manufacturers may want to test for this to ascertain if high-intensity light will cause damage such as non-linear effects (unwanted wavelength generation) or solarization or photobleaching across a spectrum of wavelengths, including down to deep ultraviolet (UV). Continuous wave lasers are not powerful enough for this level of damage testing.
When single wavelength pulse-based lasers are required, Nd:YAG (neodymium-doped ytrium aluminum garnet) lasers are an ideal option because they are relatively inexpensive and simple to use. The 1064-nm laser can also be modified using additional hardware to operate at its other harmonic frequencies: 213, 266, 355 and 532 nm. While this provides five defined wavelengths for testing, each modification adds to the cost.
There are gaps between the wavelengths—and the jump between 1064 nm to 532 nm is significant. Each of those harmonics increases the cost. Optical component manufacturers will want to know how their products perform at the wavelengths between those harmonics.
A more versatile, high-resolution option are OPO lasers that can be tuned to specific wavelengths across a wide spectrum. In this approach, OPOs convert the fundamental wavelength of pulsed mode Nd:YAGs to the selected frequency. Manufacturers such as Opotek (Carlsbad, Calif.) have developed an array of OPO technologies that ensures many wavelengths from the deep UV to the mid-infrared can easily be produced.
For example, an OPO laser can be tuned to a wavelength resolution by simply punching in a number: e.g. 410, 410.1 or 410.2 nanometers. Some tests require high-resolution wavelengths, but, with a broadband light source, you may not be able to achieve it.
Many optical components are sensitive to certain wavelengths, and destructive damage testing determines the limits of what the material can withstand. Laser-induced damage threshold testing is one example.
Certain wavelengths can trigger photochemical reactions in optical materials, changing their molecular structure or chemical composition and making them less effective. Some materials can absorb specific wavelengths of light, leading to localized heating and potential thermal damage. When the intensity of the light exceeds the damage threshold of the material, it can lead to melting, evaporation, cracking or other forms of physical damage.
Optical fibers and components often have protective coatings that are also vulnerable to damage from certain wavelengths. One of the most common applications is fiber optics, where prolonged exposure to high-intensity laser light can cause various forms of damage. To test fiber-optic strands, laser light is transmitted from one end to the other to assess the performance and characteristics of the fiber.
To determine peak power, for example, pulse based OPO lasers can deliver concentrated bursts of energy in short durations measured in nanoseconds. Because peak power is calculated by dividing the energy of a single pulse by the pulse duration, OPO lasers can deliver megawatts of energy, compared with milliwatts for continuous wave lasers.
Given the potential variety of tests at different wavelengths, optical component manufacturers would be wise to consider the merits of pulse-based OPO lasers. The flexibility and resolution provided are ideal for determining the absorption, transmission and reflection characteristics of materials and coatings, as well as damage testing. In doing so, manufacturers ensure optical products perform as expected, which can provide a competitive advantage in the optics industry.
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