Tunable Lasers Achieve Black Box Status!

Cutting-edge commercial products often originate in the field of academic research. In many cases, professors will personally start companies, or attract investors to the technology birthed in academic laboratories for licensing, so that it will be transformed into products that can be brought to market.
When academic researchers build new products, they often design and manufacture them using a number of different components. When conditions allow, they integrate off-the-shelf components into the final product. As application requirements escalate, these component parts become increasingly complex and unique.
Pulse-based tunable lasers, for example, need to be highly flexible, capable of generating a wide range of wavelengths from visible to deep ultraviolet, and outputting high-intensity pulses in nanosecond increments. They have a wide range of applications including, but not limited to, fiber optic information transmission, ion desorption, heat generation, ultrasonic generation, electronic excitation, and more. It is by virtue of their outstanding flexibility that these lasers play a vital role in the fields of time-resolved physical chemistry, mass spectrometry, photoacoustic imaging, spectroscopy, spectrophotometry, diagnostics, and hyperspectral imaging.
Among these pulsed lasers, Optical Parametric Oscillator (OPO) lasers stand out for their outstanding flexibility and economy, with the ability to be "tuned" to a wide spectral range of specific wavelengths.
OPO lasers have been commercially available for more than 35 years as the technology has evolved. Early OPO systems were so large and error-prone that they were developed and sold in garages. Today's OPOs have been transformed into fully integrated, plug-and-play devices that do not require complex setup and calibration by specialized laser engineers. Modern OPOs can be easily integrated into OEM systems with effective control.
This advancement is undoubtedly a boon to biologists, chemists, physicists, scientists and other academic researchers. While they are highly accomplished in their fields, they may not have specialized knowledge of laser design or tuning.
"Off-the-shelf OPOs are designed precisely for people who don't know much about optics or how to tune lasers," says Dr. Mark Little. He is a technical and scientific marketing consultant for OPOTEK, LLC in Carlsbad, California, the world's leading manufacturer of tunable lasers. "Basically, it's a 'black box' that can be easily integrated into another system under development."
The evolution of OPO lasers
While OPO lasers may exist today as plug-and-play devices, their evolution has not been a smooth one.
Optical parametric oscillators (OPOs) work by utilizing a crystal to convert a pulsed-mode Nd:YAG laser and its harmonics to a specific frequency. In order to achieve "tuning", both the pump laser and the OPO need to be precisely positioned. Researchers then need to manually fine-tune the crystals to the micron level until the desired wavelength is reached.
In day-to-day lab operations, researchers must be constantly on the lookout for possible misalignment of the two components. To further complicate matters, wavelengths at certain frequencies are emitted from different ports, which often requires readjustment of the external experimental setup.
The birth of OPOTEK
It was against this backdrop that academic researchers found it extremely challenging to optimize and incorporate OPOs into commercial applications.
About 45 years ago, after working for many years in the aerospace field, Dr. Margalith learned that a university in China was developing widely tunable crystals, which opened his eyes to the enormous potential of OPO lasers. At the time, tunable lasers were largely based on chemistry or dyes, which were continuous rather than pulsed and often suffered from leakage problems. In addition, due to their high complexity, bulky size and expensive maintenance costs, dye lasers never gained widespread acceptance in commercial applications.
It wasn't long before the entrepreneurial spirit of Dr. Margalith designed the first tunable OPO laser and successfully patented the technology. Since then, OPOTEK was born in his garage.
In July 1993, OPOTEK became the first company in the United States to offer broadband visible OPO. Many of the company's current products stem from this groundbreaking design. Since then, various advances in technology have continually enhanced and adapted the performance of OPOs.
Today, Dr. Margalith says the accepted method of building an OPO is to integrate the pump laser and the OPO optics in the same housing and ensure that the two cannot be separated. This design allows the entire tunable laser to be easily and safely moved as needed. Integrated software detects system alignment and makes adjustments where necessary. This stability is especially critical in commercial environments, such as when moving imaging equipment from the lab to the hospital operating room.
"Some OPOs of the past were so fragile that if the system was moved, engineers would have to realign it," explains Dr. Margalith, "This is not necessary for today's stable OPOs. Setup and training no longer require outside expertise. You can buy an off-the-shelf product and have it shipped overnight like most consumer products."
Automation now controls all system elements such as pump laser harmonics, crystal rotation optical tuning, waveform separation optics and attenuators. Product developers can also use software development kits to integrate OPO's software functionality features into their own software.
"For research scientists or companies using such lasers in their products, obtaining separate control software from tunable laser manufacturers may not be ideal. They prefer to integrate all controls into their own software. In an academic setup, saving all data on laser parameters is critical for seamless operation. Integration is the key to all functionality." OPOTEK's Dr. Little explains.
Integrating automation and control is important because typically lasers are enclosed in a larger housing, making them difficult to reprogram 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 allows them to sample incredibly small areas, measuring in tens of microns. By pre-programming the lasers, the system can rasterize and move the lasers to different areas to produce high-resolution scans.
According to Dr. Little, "Since this is a pulsed laser that emits multiple times per second, you can enter the number of times you want it to emit at each wavelength and decide to increase or decrease the number of wavelengths." "All of the high-energy beams now come from a single port, allowing the operator to target the area of interest directly for analysis."
Size is related to the tunable OPO laser. If the OPO is too large, instrument integration will be more difficult and the overall footprint of the final product will be large. This is very important considering the space requirements of a research lab.
Dr. Little first learned about OPO lasers as a graduate student at Louisiana State University. He recalls that early OPOs were "very large, difficult to use, and often damaged. One OPO was 12 feet long."
Today, OPOTEK offers one of the smallest tunable lasers on the market: the "shoebox"-sized Opolette 2940. While still requiring a "briefcase"-sized power supply with internal water cooling, the 2.94-micron OPO laser's head occupies a small footprint. While still requiring a "briefcase" sized power supply with internal water cooling, the OPO laser's 2.94 micron laser head has a 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 and further stabilizes the components within the integrated housing.
A distinguishing feature of modern OPOs is the ability to transmit a wide range of wavelengths through fiber optics. Fiber optics has become the primary method of transmitting lasers because it is easy to set up and disconnect. In addition, it protects the end user from light exposure or eye contact because the light is transmitted through a closed tube.OPOTEK offers fiber delivery for all of its products, regardless of energy level.
Historically, OPO lasers involved complex manual adjustments and precise alignment. Advances in technology have turned these lasers into plug-and-play devices that are stable and easy to use. Today's OPO lasers, which are easy to use and reliable, can be used in commercial and academic lab settings for fixture development applications.
"Academic researchers should be able to focus on their research rather than trying to tweak or fix their laser systems," states Dr. Margalith, "With a high quality OPO laser, their equipment is ready to perform out of the box."