Picosecond Transient Absorption Spectroscopy System
PicoTAS– Picosecond to Second Transient Absorption Spectrometer
About Unisoku/TII Group
As a member of Tokyo Instruments, Inc. (TII Group), UNISOKU has been developing, manufacturing and custom designing the world’s cutting-edge research instruments since 1974. It was chosen as one of Japan’s “Global Niche Top 100 Companies” by the Japanese Ministry of Economy, Trade and Industry in March 2014. It is striving to be the leading company in Japan as “No.1 in Nano-Technology measurement and Photonics”.
PicoTAS Transient Absorption Spectroscopy Systems
PicoTAS is one of UNISOKU’s newest innovative product capable of measuring Picosecond to Second Transient Absorption Spectrometer. It uses the combination of Asynchronous Pump Light and Probe Light technique and the Randomly Interleaved Pulse Train (RIPT) method. This newly patented technology allows seamless bridge of the picosecond to nanosecond time range, eliminates the notorious 1 ns – 20 ns time gap, avoids the pitfalls and limitations of optical delays in traditional pump and probe methods and nanosecond flash photolysis.
Unisoku has been developing this product in cooperation with Nihon University, Osaka University and Meijo University in the framework of the Japan Science and Technology Agency’s “Development of Systems and Technologies for Advanced Measurement and Analysis (JST-SENTAN)” program.
- Unisoku’s patented RIPT technique eliminates deficiencies of conventional TAS systems.
- Asynchronous Operation
- Complete coverage of gap time region (1 ns–20 ns)
- Broad wavelength range from VIS to NIR
- Transient absorption measurement from 100 picosecond to second
- Completely eliminates photoluminescence contamination, which has plagued conventional TAS methods.
- Can be easily upgraded to include TCSPC lifetime capability
- Compact size: can be placed on lab bench, optical bench is not required (ns model),
- Convenient to operate: No complex optical system for alignment, easy to operate, user-friendly software.
What is TAS ( Transient Absorption Spectroscopy)?
Time-resolved spectroscopy is the study of dynamic processes in materials or chemical compounds by means of spectroscopic techniques. Both TAS and Fluorescence lifetime measurement are time resolved methods, but the latter is limited to a fluorescent process at the first stage of the reaction (excited singlet state). TAS, on the other hand, can explore and analyze multi-step complex processes in a wide time region (short-lived radical species, charge transfer states, etc.), to predict emissive, non emissive states and dark states.
Conventional TAS usually refers to the pump-probe spectroscopic technique for probing and characterizing the electronic and structural properties of short-lived excited states (transient states) of photochemically or photophysically relevant molecules. In a typical conventional experimental set up, the sample is first excited by a pump pulse (pump light), then struck by a delayed probe pulse (probe light), and the impact of the probe pulse on the sample is observed by measurement of time-resolved absorption change of the probe light, analyzed against wavelength or time to study the dynamics of the excited state.
Absorbance (after pump)-Absorbance (before pump)= Δ Absorbance
Δ Absorbance records any change in the absorption spectrum as a function of time and wavelength. TAS curve along wavelength provides information of various intermediate species involved in chemical reaction at different wavelengths, and TAS against time, measured at a given wavelength, can provide information such as inter-system crossing, intermediate unstable electronic states, trap states, surface states etc.
PicoTAS from Unisoku
PicoTAS uses the Asynchronous Pump Light and Probe Light technique combined with the Randomly Interleaved Pulse Train (RIPT) method , which was featured by Science  and Nature Photonics . This is Unisoku’s newly patented technology , allows for seamless bridge of the picosecond and nanosecond time ranges, eliminating the notorious 1 ns – 20 ns time gap in conventional TAS instruments.
 Nakagawa, T.; Okamoto, K.; Hanada. H.; Katoh, R. Opt. Lett.2016, 41, 1498-1501.
 Yeston, J. Science 352, 670 (2016)
 Donati, G. Nature Photonics 10, 285 (2016)
 US Patent 9,709,497, 2017
What is Randomly Interleaved Pulse Train (RIPT) Method
The RIPT technique involves detecting the waveforms of uncorrelated pump pulses and probe pulse and calculating the time delay between the two. In the RIPT method, signal waveforms of both pump light and probe light are recorded by high-speed detectors on each pump light irradiation. The delay time of a probe pulse after the pump pulse is calculated from these waveforms. Each light intensity of probe light pulse that is transmitted through a sample is recorded by using a detector with amplifier, and the intensity is plotted against the delay time. When pump light irradiation is repeated, the delay time differs every time because pump light and probe light are asynchronous. In this way, the plot generates a continuous curve after many repeats of pump light irradiation. By executing delta optical density calculation, transient absorption curve is reconstructed. This elegant direct method avoids the pitfalls and limitations of optical delays in traditional pump and probe methods and nanosecond flash photolysis.
The main features of RIPT
- In RIPT method, the ratio between pump /probe light pulses is 1:Many, while this ratio is 1:1 for Pump-Probe method and 1: ∞ for CW method
- In RIPTI, Pump and Probe are asynchronous
- In RIPT, Time difference is calculated passively
- By repetition of pumping cycles with randomly-interleaved-pulse-train probing, TA signal with high time resolution and wide time range is reconstructed by high-speed data processing
What are the Differences between picoTAS and Conventional Techniques?
Eliminate “Gap time Region” (1-20ns):
There are mainly two conventional transient absorption (TA) techniques, Pump & Probe method and Nanosecond Flash Photolysis method. Both have difficulty in measuring the “Gap Time Region” (1‐20 nanoseconds) in which many important phenomena exist.
picoTAS uses Randomly Interleaved Pulse Train (RIPT method). It can measure wide time range of time including the time region from 1 to 20 nanoseconds.
Eliminating the influence of fluorescence:
picoTAS has the capability to eliminate the influence of fluorescence, therefore, not only non-fluorescent but also fluorescent intermediates can be detected and identified correctly. This is accomplished by picking up the signal intensity just before the rise of each probe pulse signal and repeating this procedure for a series of probe pulse train data set, and creating a background curve, which includes a photoluminescence decay signal generated by the pump pulse. Subtracting the background curve from individual probe pulse train data resulting in a transient absorption curve that is free of any photoluminescent contamination
Models: Two models of PicoTAS are offered, PicoTAS-ns (<400 ps) and PicoTAS-ps (<100 ps) depending on the pulse width of the pump laser. The configurations are flexible and can accommodate user-provided pump laser if it meets the required specs.
|Method||RIPT method (Randomly Interleaved Pulse Train method)|
|Time Resolution (10%–90% rise time)||<400 ps||<100 ps|
|Delay Time Resolution||10 ps, 20 ps, 50 ps, 100 ps, 200 ps, 500 ps, 1 ns, 2 ns, 5 ns, 10 ns, 20 ns|
|Full Scale||100 ns–2 ms|
|Wavelength Range||410–1600 nm|
|Automatic Control||wavelength scan, light intensity adjustment, shutter control|
|Sample Holder||solution (optical path length is 2 mm), thin film|
|Pump Light Source
|Source||passive Q-SW microchip laser||picosecond mode-locked laser|
|Wavelength||532 nm and/or 355 nm||532 nm and/or 355 nm and/or 266 nm|
|Pulse Width||<350 ps||<25 ps|
|Pulse Energy||>20 µJ||>80 µJ|
|Repetition Rate||100–1000 Hz (variable)||1000 Hz|
|Probe Light Source|
|Source||picosecond Supercontinuum Light Source|
|Pulse Width||<50–100 ps (dependent on wavelength)|
|Repetition Rate||20 MHz ± 5%|
|PC & Software|
|Function||Automatic reconstruction of transient absorption temporal profile, curve fitting (nonlinear least square method), data storage in text format|
|Installation Environment||no optical bench required||on optical bench|
* Specifications are subject to change without notification
* Our engineers will help to configure your customized system.
Dimensions of Optomechanical Unit
*Installation spaces for probe light source, PC and oscilloscope are needed separately.
**-ps model further requires an installation space for pump light source.
1. Wavelength-Tunable Pump Light Source for -ps model
Variable excitation wavelength
|Type||Optical Parametric Generator (OPG)|
|Pump Laser||Picosecond mode-locked laser 1kHz, 355 nm, 0.3W|
|Wavelength Range||410-709 nm, 710-2300 nm|
2. CoolSpeK Low-Temperature Cell Holder (for 2mm cell)
Temperature Range from -180°C to +100°C
|Temperature Range||-180℃ ～100°C|
|Temperature Control||Flow control of liquid nitrogen by an automatic valve|
|Functions||Low Dew Condensation by Heating of Optical Window, Stirrer|
|Liquid Nitrogen Reservoir||Stainless, 2L
Duration of 2H at -80℃
4. Global Analysis Software
Spectrum Analysis of Multicomponent and Various Analysis Functions
|Software||Globalworks – made by US Company OLIS|
|Analysis Feature||Singular Value Decomposition (SVD),
Customized system with existing pump light source and/or probe light source.
|Recommended Specification for Pump Light Source||Repetition rate 1 kHz,
Pulse width <500 ps,
Output energy 20 μJ/pulse
※Please contact us for the source out of the specification above
|Recommended Specification for Probe Light Source||1. Supercontinuum light source with repetition-rate of 20 MHz
2. Supercontinuum light source equipped with a pulse picker (Settable at 20 MHz.）
3. Picosecond laser diode with high output energy (100nJ/pulse)
Notes: System performance might be limited depending on the specifications of pump light source and/or probe light source.
Please feel free to contact us for the transient absorption system that can eliminate long-lived luminescence by making the most use of the RIPT method and a lower repetition-rate supercontinuum light source