07/16/2026
High-Rep-Rate Tunable Laser Sharpens Nanosecond Transient Absorption Spectroscopy
A high-repetition-rate, tunable laser improves resolution in nanosecond transient absorption spectroscopy by increasing data collection speed and enhancing statistical averaging. When integrated with an advanced spectrometer, this approach expands the dynamic range of TAS experiments.
Nanosecond transient absorption spectroscopy (TAS) is a time-resolved pump-probe technique that reveals how molecules and materials behave in the first moments after they absorb light. Instead of producing a single static absorption spectrum, the method tracks how the spectrum evolves over time after a short excitation pulse from a laser.
The reason why TAS is such an effective tool is that it allows researchers to measure dynamic behaviors that cannot be measured through steady state spectroscopy. A number of significant photophysical and photochemical processes such as triplet and charge-carrier dynamics, exciton migration, and metastable photochemical intermediates, occur in the nanosecond to millisecond time domain and often produce weak, transient absorption features that require sensitive time-resolved spectroscopy for detection.
By directly measuring these short-lived spectral changes, nanosecond TAS gives researchers insight into the relationship between molecular structure and functional performance in photovoltaic devices, photocatalytic systems, light harvesting assemblies, biological chromophores, conductive polymers, and new energy conversion materials.
Now advances in laser technology are rapidly redefining the operational limits of nanosecond TAS. In particular, the emergence of tunable, high repetition rate lasers that dramatically increase pulse delivery frequency while maintaining ultrafast temporal resolution.
Tunable lasers allow researchers to precisely adjust the excitation wavelength in the UV, Visible and Near-Infrared (NIR) portions of the spectrum. At high repetition rates, these systems increase the amount of data collected per unit time, which reduces the effect of random noise on the measured signals and improves detection of weak transient components. The result is a more complete study of the kinetics of the system and a better understanding of the dynamic processes that occur.
The Excitation Laser
In a basic TAS setup, a nanosecond or shorter pump pulse excites a portion of the sample from the ground state into an electronically excited state. A weaker probe beam then passes through the same region at a controlled delay. By comparing the probe transmission with and without excitation, the system produces a wavelength-resolved differential absorption signal.
The laser light source contributes significantly to the overall performance of the measurement system. Pulse duration defines the achievable temporal resolution. Pulse energy governs how effectively the pump pulse drives measurable population changes within the sample. Source stability is essential to maintain clean differential signals and prevent noise from obscuring subtle effects.
The laser's repetition rate is also an important factor in determining the ability of the transient absorption technique to produce high quality measurements. Although it affects both the amount of signal averaging that can be performed as well as the quality and throughput, it is often overlooked when evaluating a system.
Until recently, however, most tunable lasers have been limited to an operating repetition rate of 10-20 Hz. Exceeding this threshold requires a new generation of diode-pumped solid-state (DPSS) lasers capable of operating at 100 Hz or higher.
Improving Signal-to-Noise Ratio to Improve Kinetic Clarity
One of the principal challenges in TAS is detecting weak signals that are frequently masked by electronic noise. Traditionally, improving the signal-to-noise ratio (SNR) in TAS measurements involves averaging the results of multiple experiments, where the SNR increases with the square root of the number of averaged data points. Averaging one hundred measurements only reduces the noise level tenfold, for instance.However, when using lower repetition-rate lasers, this method is time-consuming and impractical when repeated measurements are required. Fluctuations in the pump laser's shot-to-shot stability and drifts in the probe light source's intensity can also affect the SNR of TAS measurements during long data collection periods.
Additionally, SNR can still be poor even after prolonged scanning when using this approach, specifically when probing the vibrational dynamics of materials following photoexcitation. The signals generated from these dynamic processes are typically weak and therefore difficult to detect due to the presence of unwanted electrical noise; in fact, several hours of collected data may not be enough to adequately remove unwanted noise.
At higher repetition rates, more pump-probe pulses can be collected in less time with fewer variances in the entire system, thus improving the signal-to-noise ratio and enabling the use of lower pulse energies. Gentler excitation conditions reduce the risks of cumulative heating or photodamage and shorten the time required to obtain a full kinetic map.
However, the rate cannot be pushed too high, since samples must have time to relax or exchange between pulses. A 100 Hz excitation source strikes a desirable balance for many nanosecond-scale systems: fast enough to achieve efficient averaging, yet slow enough for most condensed-phase samples to fully recover between pulses.
A stable, tunable pump laser operating at 100 Hz provides an efficient and practical solution for a wide range of nanosecond and microsecond applications. In this context, high speed and high sensitivity are closely linked. According to Eric Kennehan, Ph.D., Co-founder & CEO of Magnitude Instruments, his doctoral research centered on transient absorption studies of photovoltaic materials, which required extensive use of TAS.
At the time, he found the available TAS instrumentation cumbersome, slow, and lacking in sensitivity. The limitations of the equipment spurred him to collaborate with colleagues to design and build an improved spectrometer so that he could spend less time in the lab and more time analyzing data and writing papers.
To improve SNR, the company has prioritized the development and implementation of advanced noise suppression technologies (NSTs). NSTs enable the precise subtraction of electronic artifacts that traditionally obscure weak signals in TAS measurements. This advancement allows researchers to collect the entire time axis for TA measurements directly from the detector response with each laser shot, dramatically accelerating data collection times and enhancing accuracy.
The incorporation of patented noise suppression technologies has enabled an enhancement of more than two orders of magnitude in the speed and sensitivity of transient absorption measurements on the nanosecond-to-millisecond timescale. Previously, the strategy to improve signal detection in TAS was to increase the pump fluence, thereby increasing the total number of excited states that could be probed. While this approach can improve signal visibility, it also may induce nonlinear interactions among excited states.
Such interactions occur when the high concentration of excited states begin interacting with one another, which can complicate and often obscure the interpretation of the results. Critically, elevated pump fluences can also hasten sample degradation, notably affecting sensitive biological specimens or materials prone to photodegradation.
Biological samples such as proteins and enzymes are highly susceptible to pump fluence. Excessively high laser fluences, as commonly employed in earlier approaches, can damage the sample, increasing the likelihood that the measured signals reflect laser-induced damage rather than the sample's intrinsic function or catalytic properties.
Integrating Tunable Lasers
For most applications, a fixed wavelength Nd:YAG laser capable of generating excitation wavelengths of 1064, 532, 355, and 266 nm is included in nanosecond TAS systems. However, when a project requires wavelength flexibility, Magnitude Instruments integrates an OPO (optical parametric oscillators) or OPA (optical parametric amplifier) sourced from a qualified supplier.The ability to vary the wavelength enables researchers to select and activate discrete electronic or vibrational transitions within their samples with a high degree of precision and control. This allows researchers to achieve more detailed and application-specific results from their experiments.
According to Kennehan, Magnitude Instruments was recently approached by a researcher at a leading university seeking information about the company's benchtop systems. A primary requirement was the integration of an OPO capable of operating at high repetition rates to meet the demands of the intended applications.
Operating a tunable laser at 100 Hz enables significantly faster data acquisition by the spectrometer. At 100 Hz compared with 10 Hz, data collection proceeds approximately ten times faster under otherwise equivalent conditions. Higher repetition rates also reduce background interference, leading to cleaner signals and improved overall data quality.
High repetition rates also enable Magnitude Instruments to detect weaker signals while operating at lower laser fluences. This approach minimizes the risk of sample damage or degradation during measurement. At the same time, it reduces complications such as nonlinear effects, multi-exciton generation, excited-state annihilation, and thermal artifacts that can develop on nanosecond to microsecond timescales.
- OPOTEK Opolucis C
Magnitude Instruments previously collaborated with OPOTEK on multiple installations, including projects that incorporated OPOs operating at 20 Hz. However, OPOTEK recently introduced a new family of DPSS-based OPO lasers, the Opolucis C, that can deliver a repetition rate of 100 Hz and peak OPO energy of up to 45 mJ per pulse.
Historically, the adoption of diode-pumped lasers was constrained by the high cost and limited supply of high-power diode assemblies. Producing these diodes required a specialized manufacturing process, and only a small group of global suppliers had the capability to deliver devices that met the performance demands of high-energy laser systems. Fortunately, recent improvements in diode fabrication and supply availability have made this approach commercially viable for use in OPO lasers. The compact footprint of the Opolucis C was particularly compelling, as reducing overall system size remains a central design objective for Magnitude Instruments.
Historically, transient absorption spectroscopy setups have posed considerable challenges for many laboratories due to the large, complex, and expensive nature of the equipment required to make TAS measurements. As a result, Magnitude Instruments has consistently emphasized developing a true benchtop system that can be integrated seamlessly into standard laboratory environments.
The ongoing effort to reduce the size limits of spectrometers requires compact laser systems, as earlier configurations paired with OPOs often resulted in laser systems that were as large as or larger than the spectrometer itself. As nanosecond transient absorption spectroscopy continues to gain traction in biotechnology and medical research, high-repetition-rate lasers are becoming less of a premium feature and more of a practical necessity. With high-repetition-rate lasers, data collection is much faster, enabling scientists to sample and process more points in an order of magnitude less time.
By dramatically increasing the number of pulses per second, scientists can collect and evaluate many more data points in about one order of magnitude less time than with low-repetition-rate lasers. As laser platforms continue to evolve toward higher stability, greater tunability, and scalable repetition rates, their integration into TAS setups is expected to significantly enhance both performance and experimental versatility. This progression opens new possibilities for investigating nanosecond time scale phenomena in increasingly complex systems.