Fundamentals of Ultrafast Spectroscopy
Lecture 1
-- Introduction of Ultrafast Spectroscopy
Jinhui Zhong 钟锦辉
Department of Materials Science and Engineering
Southern University of Science and Technology
zhongjh@sustech.edu.cn
About This Lecture
3 Credit points, 16 weeks, 48 learning hours
Odd-week, Thursday
Even-week, Wednesday + Thursday
3 learning hours per week
About This Lecture
3 Credit points, 16 weeks, 48 learning hours
Section 1
Section 2
Section 3
Section 4
Section 5
超快光谱学导论 Introduction of ultrafast spectroscopy
光与物质相互作用基础 Fundamentals of light-matter interaction
线性与非线性光学效应 Linear and nonlinear optical effects
超短脉冲的制备与表征方法 Generation and characterization of ultrashort laser
pulses
超快光谱方法 Ultrafast spectroscopic methods
Ultrafast fluorescence, pump-probe/Transient absorption spectroscopy, and twodimensional spectroscopy
Section 6
Section 7
超 快 光 谱 学 在 材 料 、 化 学 、 物 理 等 领 域 的 应 用 实 例 Examples of the
applications of ultrafast spectroscopy in materials science, chemistry, and
physics
超快光谱学的未来发展趋势 Perspective of ultrafast spectroscopy
An Introduction of Myself
• Education
• 2006.09-2010.07
BS Materials Chemistry, Sun Yat-Sen University
• 2010.09-2016.06
PhD Physical Chemistry, Xiamen University, Prof. Dr. Bin Ren
• Working/Research Experience
• 2016.07-2017.02 Xiamen University, Research Assistant
• 2017.02-2022.02 Carl von Ossietzky Universität Oldenburg (Germany)
Postdoctoral researcher, Alexander von Humboldt Fellowship
Prof. Dr. Christoph Lienau
• 2022.02-to date Southern University of Science and Technology
Assistant Professor
Electromagnetic Spectrum
Electromagnetic Spectrum
What do we see?
What do we see?
Metal reflects light
Glass transmits light
Ozone absorbs (UV) light
Milk scatters light
(Sky/Water)
Molecules and Spectroscopy
• Length of chemical bonds: C-H、O-H…..
纳米nm（10-9m）、埃Å（10-10m）
• Molecular spectroscopy：
Absorption吸收—UV, Vis, Infrared紫外、可见、红外等
Emission发射—Fluorescence, phosphorescence荧光、磷光等
Scattering散射—Raman、X-ray、electron等
质谱、NMR、EPR等
• Features of spectroscopy：
Qualitative定性—分子的结构：特征峰、“指纹”
Quantitative定量—分子的含量：峰的强度
• 动力学与分子相互作用：谱峰的形状
Typical molecular spectra
2E
g
钛宝石的吸收
和发射光谱
How fast are these processes?
2T
2g
intensity (a.u.)
Raman spectrum of ethanol
CH3 – CH2 – OH
s(CH2)
s(CH3)
a(CH3)
(CH3), (CO)
(CC)
pump
(OH)
(OH) (CH)
1000
1500
2000
wavenumber
2500
(cm-1)
3000
3500
Molecular “Dancing”—Vibration
• 振动模式和振动频率：伸缩、剪切（弯曲）、扭曲…..
C-H伸缩 ~2900cm-1 （振动周期~10 fs， 10-14秒）
The fastest vibrations in nature have an oscillation time of 10 fs.
Monitoring molecular “dancing” – Ultrafast spectroscopy
看分子“跳舞”—超快时间分辨光谱
Relevant Time Scales
超快时间尺度 Dynamics Time scales
1 millisecond (ms)
1 microsecond (s)
1 nanosecond (ns)
1 picosecond (ps)
1 femtosecond (fs)
1 attosecond (as)
= 110-3 s
= 110-6 s
= 110-9 s
= 110-12 s
= 110-15 s
= 110-18 s
超快现象-Ultrafast Phenomena
• A few relevant time scales：纳秒（ns）10-9s、皮秒（ps） 1012s、飞秒（fs）
10-15s、阿秒attosecond 10-18s
speed of light: 3 x 108 m/s = 300 nm/fs
• 超快过程或超快现象（Ultrafast）：
Physical/Chemical Processes occurring in a <1 ns time
scale
Molecular vibration, breaking/forming of a chemical
bond, collision of molecules in solution,
energy/charge transfer, proton transfer
Ultrafast Phenomena
International Conference on Ultrafast Phenomena
2020, 22nd in Shanghai, China
2022, 23rd in Vitoria, Canada
The spatial extent of light
1 s ➔ 300,000 km
(~3/4 the distance from the Earth to the moon)
1 ns ➔ 30 cm
(the nanosecond is the approximate time scale for high-speed
electronic chips and computers)
https://nineplanets.org/questions/how-far-is-the-moon/
Ultrafast optics
1 ps ➔ 300 m
(thickness of a business card)
1 fs ➔ 300 nm
The Horse in Motion
Bet: Do all four hooves of a trotting horse evern simultaneously leave the ground?
How can we measure things this fast?
–6
Timescale (seconds)
10
–9
10
Electronics
–12
10
Optics
–15
10
1960
1970
1980
Year
1990
2000
Time-Resolved Spectroscopy
Pump-probe spectroscopy
• 泵浦pump（激发）：引发体系的变化、确定
时间零点，通常是把分子激发到激发态
• 探测probe：实时跟踪体系的变化
监视反应物、中间物、产物等
t=0
Experimental pump-probe setup
• 光速：3x108 m/s（真空）
• 光程：Optical Path
1微米（10-6 m）
相当于3.33x10-15 秒
• 时间的起点：initiation
Pump-Probe Technique-A video illustration
http://toutestquantique.fr/en/
Following the inter-atomic distance change
• 分子中原子的移动速度: ~1000 m/s
• 看到化学键变化需要的空间分辨率: ~0.1 Å (10-11 m)
• 实时跟踪化学反应需要的时间分辨率:
10-11 m/(1000 m/s) = 10-14 s = 10 fs！
Photodissociation of
I2/benzene
Conical intersection dynamics of the primary
photoisomerization event in vision
视网膜上的光化学反应：视觉的基础
Cerullo, G. Conical intersection dynamics of the primary
photoisomerization event in vision. Nature 2010, 467, 440-443.
Interferometric frequency-resolved autocorrelation (IFRAC)
探测飞秒相干动力学
泵浦-探测时间延迟
二阶非线性光谱

Mirror
BS
80 MHz
L = 880 nm
t ~ 8 fs

Dichroic
mirror All-reflective
objective
Sample
Spectrometer
C Lienau, et al. Nat. Photon. 2012, 6, 293-298. T. Hanke, A. Leitenstorfer, R. Bratschitsch, et al. Nano Lett.
2012, 12, 992. Phys. Rev. Lett. 2009, 103, 257404. Steinmeyer, G. et al. Rev. Sci. Instrum. 2017, 88, 103102.
Nobel Prize in Chemistry 1999: A. H. Zewail
The Nobel Prize in Chemistry 1999 was awarded to Ahmed
H. Zewail "for his studies of the transition states of
chemical reactions using femtosecond spectroscopy"
The Nobel Prize in Physics 2005
光学频率梳
The Nobel Prize in Physics 2018
CPA-啁啾脉冲放大
Femtosecond Laser for Surgery
Myopia近视
Eye surgery
120 nJ/pulse
focused to a few micrometres
Characteristics of Ultrashort Pulses

t
激光线宽
Spectral width
脉冲宽度
Time duration
Pulse width
测不准关系： Uncertainty principle:
As the pulse duration decreases, the
bandwidth increases correspondingly.
E×t ≥ h/4
Characteristics of Ultrashort Pulses
• High bandwidth. By the uncertainty principle, the product of the
pulse-width (t) times the optical bandwidth () must be of order
unity (or larger). This high-bandwidth feature can be important for
optical communications as well as other applications.
Time-bandwidth product
t: Full width at half maximum (FWHM半高宽) of the temporal intensity
profile 𝐼 t = 𝐸(𝑡) 2 .
: FWHM of the spectral intensity profile 𝐼  = 𝐸() 2 .
Pulse-width (t) vs the Optical bandwidth ()
Fourier transform limited pulse (no chirp)
5.6 fs, 184 nm (FWHM)
9.2 fs, 110 nm
27 fs, 36 nm
Pulses of 100 fs have bandwidths on the order of 10 terahertz (THz), and the
shortest visible laser pulses contain so much of the visible spectrum that they
appear white.
The pre-condition to have an ultrashort pulse is to have a broadband spectrum.
Time-Bandwidth Product of Different Pulse Shapes
A sub-10 fs pulse
9.2 fs, 110 nm
Characteristics of Ultrashort Pulses
• Potential for high intensity. For a given pulse energy, the peak
power and peak intensity are inversely proportional to the pulse
duration. Because the size (hence cost) of high-power lasers
usually scales with pulse energy, femtosecond pulse technology
can be used to obtain ultrahigh peak intensities at moderate
energy levels. Amplified femtosecond pulses have produced peak
powers up to the petawatt level (1 petawatt = 1015 W) and peak
intensities exceeding 1020 W/cm2.
Summary
• Relevant time scale for ultrafast spectroscopy
• Characteristics of ultrashort pulse
• Uncertainty principle applies for laser pulse
Some suggestions/requirements
for attending this lecture
1. Take a notebook and a pen (writing down is always better
than just listening)
2. A laptop installed with Matlab, a very useful software for
mathematical calculation and simulation
-SUSTech library
-will show examples and you will need to practice to learn
Matlab in SUSTech Library
Course Assessment 课程考核
出勤Attendance（10%）、课堂表现Class Performance（10%）
、小测验Quiz（20%）、平时作业Assignments（20%）、课程
项目Projects（20%）期末报告Final Presentation（20%）
Thank you for your attention!
Questions
Relevant Time Scales
1 millisecond (ms)
1 microsecond (s)
1 nanosecond (ns)
1 picosecond (ps)
1 femtosecond (fs)
1 attosecond (as)
One femtosecond is 10–15 seconds, that is, 0.000000000000001 seconds
= 110-3 s
= 110-6 s
= 110-9 s
= 110-12 s
= 110-15 s
= 110-18 s
Characteristics of Ultrashort Pulses
•
High time resolution. By definition, the pulse duration is in the
picosecond or femtosecond range (or below). This provides very high
time resolution for excitation and measurement of ultrafast physical
processes in solid-state, chemical, and biological materials.
•
High spatial resolution. The spatial extent of a short light pulse is given
by the pulse duration multiplied by the speed of light. As noted above,
for very short pulse durations, the spatial pulse length can be on the
order of micrometers. This makes ultrashort pulses useful for some
microscopy and imaging applications.