Tunable Lasers Achieve Black Box Status

The OPO has developed into a plug-and-play device that can be easily integrated into larger systems.

Modern OPOs are user-friendly, integrated systems easily installed and controlled without extensive expertise.
Modern OPOs are user-friendly, integrated systems easily installed and controlled without extensive expertise.

Cutting-edge commercial products often originate within the academic research community. In many cases, professors establish companies themselves and/or investors express interest in licensing technology born in academic laboratories to develop into marketable products. 

In creating new products, academic researchers typically design and build using various component parts. When possible, off-the-shelf components are integrated into the final product. The more advanced the application, the more complex and unique component parts are likely to be. 

Pulse-based tunable lasers are a good example. These lasers must be flexible enough to produce wavelengths across a broad spectrum from visible light to deep UV, in high intensity bursts measured in nanoseconds. Pulse-based tunable lasers can transmit information over fiber, desorb ions and generate heat that is converted to ultrasonic waves or excite electrons. Their flexibility enables lasers to play a critical role in time-resolved physical chemistry, mass spectrometry, photoacoustic imaging, spectroscopy, spectrophotometry, diagnostics and hyperspectral imaging.

Optical Parametric Oscillators (OPO) are a notable type of tunable laser, now a commercial reality after 35 years of development.Optical Parametric Oscillators (OPO) are a notable type of tunable laser, now a commercial reality after 35 years of development.OPOTEK LLC

Among the most flexible and inexpensive pulse-based lasers are Optical Parametric Oscillators (OPO) lasers that can be “tuned” to a wide spectrum of specific wavelengths. 

Thanks to more than 35 years of development, OPO lasers are a commercial reality. From the early days as a large, easily misaligned system developed and sold out of a garage, OPOs are now fully integrated, off-the-shelf devices. And they no longer require a laser engineer to set up and calibrate. Today’s OPOs are readily installed and controlled in an OEM’s system.

This is a welcome development for biologists, chemists, physicists, scientists and other academic researchers who possess in-depth knowledge of their fields but lack expertise in laser design or tuning. 

“Off-the-shelf OPOs are designed specifically for those who don't know much about optics or how to tune a laser,” said Dr. Mark Little, Technical and Scientific Marketing Consultant for Carlsbad, CA-based OPOTEK LLC, a global manufacturer of tunable lasers. “Basically, it is a black box that can be integrated into another black box that is being developed.” 

The Evolution of the OPO Laser

Today’s OPO lasers may be plug-and-play devices, but that was not always the case. 

Optical parametric oscillators (OPO) work by using a crystal to convert the fundamental wavelength as well as its harmonics of pulsed mode Nd:YAG laser to a selected frequency. To “tune” the lasers, both the pump laser and the OPO had to be precisely positioned. Crystals then were manually rotated using micrometers until the desired wavelength was achieved. 

Researchers had to watch for misalignment of the two components caused by routine lab activities. Also, wavelengths at certain frequencies were emitted from separate ports. This required repositioning the external experiment.

These lasers are vital for various scientific applications, including mass spectrometry and photoacoustic imaging.These lasers are vital for various scientific applications, including mass spectrometry and photoacoustic imaging.OPOTEK LLC

As a result, academic researchers found it challenging to optimize lasers and incorporate OPOs in commercial applications. 

After years in the aerospace sector, Dr. Eli Margalith the potential of OPO lasers struck him when he learned about broadly tunable crystals being produced at a Chinese university almost 45 years ago. At the time, the only tunable lasers were chemical or dye based. Continuous and not pulse-based, these lasers often had leakage issues. Moreover, due to their overall complexity, size and costly maintenance requirements, dye lasers never gained traction in commercial applications.

Shortly thereafter, the entrepreneurial Dr. Margalith designed his first tunable OPO laser, patented the technology and OPOTEK was born in his garage. In July 1993, OPOTEK became the first company in the United States to offer a broadband, visible OPO. Numerous current products from the company stem from his original designs. Various advancements have enhanced and fine-tuned the technology since that time.

Today, Dr. Margalith says the accepted way to construct a complete OPO is to integrate the pump laser in the same housing as the OPO optical assembly, securing it in a manner that neither can move. This allows the complete tunable laser to be easily and safely moved as needed. Integrated software allows the system to check for alignment and make adjustments if needed. In commercial settings - such as moving imaging equipment from a lab to a hospital's operating room - stability is a necessity.

“Some OPOs in the past were so delicate that if the system is moved, an engineer would have to realign it,” explained Dr. Margalith. “With today’s stable OPOs that is unnecessary. Set up and training no longer require outside expertise. You can buy them off-the-shelf and shipped overnight like most consumer products.” 

Automation now controls all system elements, such as the pump laser harmonics, crystal rotation for optics adjustment, waveform separation optics and attenuators. Product developers can also incorporate the software functionality features of the OPO into their own software using software development kits.

“For research scientists or companies utilizing this laser in their products, having separate control software from the tunable laser manufacturer may not be ideal. They prefer to integrate all controls into their own software. In academic settings, saving all data with laser parameters is crucial for seamless operation. Integration is key for everything to function cohesively,” explained OPOTEK’s Dr. Little.

Integrating automation and control is important as often lasers are enclosed within a larger housing, making it difficult to access for reprogramming or repair.

The software development kit can also be used to set up programmable scans with pre-determined wavelengths in any order. This has applications in advanced, high-resolution imaging. The inherent focusability of lasers enables them to sample incredibly small size areas, measured in tens of micrometers. By pre-programming the laser, the system can raster and move the laser to different areas to produce high resolution scans.

“Since it is a pulse laser that lases many times per second, you can enter the number of times you want it to fire at each wavelength and determine how much to increase or decrease the wavelength,” said Dr. Little. “All the high-powered beams now come out of a single port, allowing the operator to directly target the area of interest for analysis.” 

Size matters with tunable OPO lasers. If an OPO is oversized, instrument integration will be more difficult and the overall final product footprint large. This can be significant given research lab spatial requirements.

Dr. Little first learned about OPO lasers as a graduate student at Louisiana State University. He recalls early OPOs were “very large, hard to use and broke down a lot. One OPO was 12 feet long.”

Pulse-based tunable lasers offer broad-spectrum wavelengths in intense bursts.Pulse-based tunable lasers offer broad-spectrum wavelengths in intense bursts.OPOTEK LLC

Today, OPOTEK offers one of the smallest tunable lasers commercially available, the ‘shoebox’ sized Opolette 2940. While still requiring a ‘briefcase’ sized power supply with internal water-cooling, the 2.94 micron OPO laser has a laser head footprint of only 9.5 x 4.5 x 7.5 inches, 

According to Dr. Little, the small size increases the rigidity of the laser, further stabilizing the component parts within the integrated housing. 

One notable feature of the modern OPO is the ability to transmit various wavelengths through fiber optics. Fiber optics has emerged as the primary method for transmitting laser light due to its ease of setup and disconnection. Moreover, it safeguards end users from light exposure or eye contact, as the light is conveyed through an enclosed conduit. OPOTEK provides fiber delivery for all its products, irrespective of the energy levels.

Historically, the OPO laser involved complex manual adjustments and precise alignments. Advancements have transformed these lasers into plug-and-play devices, stable and easy to use. Today’s OPO lasers, easy to use and reliable, can be fixtures developing applications in commercial and academic lab settings.

“Academic researchers should be able to focus on their research instead of trying to tune or repair the laser system,” said Dr. Margalith. “With a quality OPO laser, their device is going to do what it is supposed to do right out of the box.”

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