OPTOELECTRONICS
OPO Lasers Put Optical Components to the Test
OPO lasers test optical fibers and components to characterise the spectral response of optical components, which can provide a competitive advantage in the optics industry.
O
ptical parametric oscillator (OPO) lasers have long been utilised in sophisticated test and measurement applications such as mass spectrometry, photoacoustic imaging, and spectroscopy. Now, these “tunable” pulsed lasers are being utilised 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.
Lasers, in general, have long been utilised in the test and measurement of optical materials. 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 quality of the product, which is a factor that 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. They can also be used to assess how coatings on optical surfaces will perform. Damage testing has become even more important to identify given optical materials can be damaged at different wavelengths. Coatings can also become compromised at specific wavelengths, leading to 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 in the types of tests that can be performed and decreases complexity so manufacturers can ensure optical products perform as expected,” says Dr. Mark Little, Technical and Scientific Marketing Consultant for OPOTEK, LLC, a global manufacturer of tunable lasers for research and diagnostics,
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Because peak power is calculated by dividing the energy of a single pulse by the pulse duration, OPO lasers can deliver megawatts of energy, versus milliwatts for continuous wave lasers.
with solutions for photoacoustic, spectroscopy, diagnostics, hyperspectral imaging, and medical research.
Little adds that there can be significant advantages to using pulse-based lasers. Although continuous wavelength lasers are an inexpensive solution for testing optical materials, they don’t 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 solarisation or photobleaching across a spectrum of wavelengths, including down to ‘deep’ UV,” explains Little, adding that continuous wave lasers are not powerful enough for this level of damage testing. When single wavelength pulse-based lasers are required, Nd:YAG lasers are an ideal option because they are relatively inexpensive and simple to use. The 1064-nm laser can also
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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,” says Dr. Little, adding that each of those harmonics increases the cost. “Optical component manufacturers will want to know how their products perform at the wavelengths between those harmonics.” According to Little, a more versatile, high- resolution option are OPO lasers that can be “tuned” to specific wavelengths across a wide spectrum. In this approach, optical parametric oscillators (OPO) convert the fundamental wavelength of pulsed mode Nd:YAGs to the selected frequency. Leading manufacturers like Carlsbad, CA-based OPOTEK have developed a diverse array of OPO technologies that ensures that many wavelengths from the deep UV to the mid- infrared can easily be produced. “An OPO laser can be tuned to a very specific wavelength resolution by simply punching in a number like 410, 410.1, or 410.2 nanometers,”
Photo: Optical engineering
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