Transient absorption

What is a transient absorption measurement?
Measurement principle of transient absorption
Excited state dynamics
Detection techniques
Advantages
Example of transient absorption measurement
Featured products and systems

What is a transient absorption measurement?

Transient absorption measurement is a sophisticated technique employed to generate and measure transient species, such as excited molecules and radicals, upon the irradiation of a sample with a pulsed laser. This method facilitates the measurement of the absorption spectrum of these transient species and their temporal variations. The data obtained provide insights into the excited states of molecules, the dynamics of excited molecules, and the photolysis processes of compounds, thereby enabling the tracing of photophysical and photochemical processes in light-emitting materials and devices.

Measurement principle of transient absorption

The transient absorption measurement relies on the use of two light pulses, as depicted schematically in Figure 1. The pump light serves to excite the sample, while the probe light detects the changes induced by the pump light. This technique is thus referred to as the pump-probe method. Typically, a high-power laser, such as Nd: YAG, is utilized as the pump light, and a broadband light source, such as a Xe lamp, is employed for the probe light.

Upon irradiation with the pump light (pulsed laser), certain molecules within the sample absorb the light and transition to an excited state. By measuring the probe light as the molecules revert to their ground state, the absorption spectrum of the excited molecules and its temporal evolution can be recorded.

過渡吸収測定系の模式図

Figure 1: Example of a transient absorption measurement system configuration

Excited state dynamics

In the excited state, the sample generally exhibits a distinct absorption spectrum compared to its ground state. The excited molecules gradually return to the ground state over time. By repeatedly measuring the absorption spectrum before all molecules return to the ground state, the temporal changes in the absorption spectrum can be captured (Figure 2).

過渡吸収測定の原理

Figure 2: Principle of transient absorption measurement

Detection techniques

When using a photomultiplier tube (PMT) as a detector, it is necessary to repeatedly irradiate the sample with pump and probe light, shifting the measurement timing to accumulate data. Hamamatsu Photonics’ transient absorption measurement system, featured as a time-resolved absorption spectroscopy analysis system (TRASS), deploys a streak camera combined with a spectrometer, as illustrated in Figure 3.

過渡吸収測定装置の構成例

Figure 3: Example of transient absorption measurement system configuration

Advantages

The TRASS system utilizing the streak technique is extremely valuable because it enables the acquisition of all temporal information in a single excitation event. This one-shot measurement approach not only reduces the overall measurement time but is also advantageous for samples susceptible to optical degradation.

Example of transient absorption measurement

Transient absorption time-resolved spectroscopy of the triplet-triplet annihilation reaction process of anthracene in supercritical carbon dioxide (40°C, 10.9 MPa)

超臨界二酸化炭素中 (40 ℃、10.9 MPa)のアントラセンの三重項-三重項消滅反応過程の過渡吸収時間分解分光

超臨界二酸化炭素中 (40 ℃、10.9 MPa)のアントラセンの三重項-三重項消滅反応過程の過渡吸収スペクトル

三重項アントラセンのモル吸光係数の圧力依存性（40℃）

Data courtesy of: National Institute of Advanced Industrial Science and Technology Supercritical Fluid Research Center (Sendai City, Japan)

Researcher: Dr. Takafumi Aizawa

Time-resolved transient absorption spectral streak image in simultaneous observation of the singlet-singlet absorption and the triplet-triplet formation of Anthracene solution

アントラセン溶液の一重項－一重項消滅反応過程と、三重項－三重項生成反応過程の同時計測

Featured products and systems

Time-resolved absorption spectrum analysis system

Measures transient absorption spectra in the picosecond to nanosecond time region. Time-resolved measurement of multiple wavelengths simultaneously in a single shot makes it possible to capture irreversible phenomena.

High dynamic range streak camera

The C13410 is a high dynamic range streak camera that can handle a large number of photo-electrons. This feature enables single-shot measurements of ultra fast phenomena with a dynamic range as high as 10 000 : 1.