光电子技术 精品课程
飞秒脉冲的测量方案 电子科学与技术 (Measurement of an ultrashort pulse) 精密仪器与光电子工程学院
Outlines
为什么测量超短脉冲是一项挑战? 为什么 要对超短脉冲进行测量? 对超短脉冲的全面描述需要那些测量量？ 光谱仪与Michelson 干涉仪 自相关法 频率分辨光学开关法 (FROG) 光谱相位干涉直接电场重构法 (SPIDER)
What if we use a collinear beam geometry, and allow the autocorrelator signal light to interfere with the SHG from each individual beam?
Michelson Interferometer
SHG-FROG and other geometries
XFROG, Single-shot FROG and GRENOILLE
频率分辨光学开关法 (FROG)
FROG： 用复制的可延迟的脉冲与原脉冲在非线性介质中的瞬时相 互作用作为光学开关；对开关脉冲随时间的变化进行光谱分辨。
Pulse to be measured
Nonlinear medium (glass)
Esig(t,) = E(t) |E(t-)|2
Use any ultrafast nonlinearity: Second-harmonic generation, etc.
SHG FROG Measurements of a 4.5-fs Pulse!
“Polarization Gate” Geometry
Beam splitter E(t-)
I FROG ( , )
45° polarization rotation


2

Esig (t , ) exp( i t ) dt
Camera
Variable delay,
E (t )
Iaconis and Walmsley, JQE 35, 501 (1999).
SPIDER apparatus
Delay Line M BS Delay Line
Focusing Lens
Lens
Spectrometer
SHG crystal
Filter Aperture
BS
Pulse Stretcher
This pulse sums with the blue part of the chirped pulums with the green part of the chirped pulse.

t
t
SFG


Performing SI on these two pulses yields the difference in spectral phase at nearby frequencies (separated by ). This yields the spectral phase.
Michelson Interferometer
Grating
Input
BS
BS
Grating
~ ~ ~ ~ S ( , ) | Etest ( 1 ) |2 | Etest ( 2 ) |2 | Etest ( 1 ) || Etest ( 2 ) | cos[ test ( 1 ) test ( 2 ) ]
How SPIDER works
Input pulses
Chirped pulse t
Output pulses Two replicas of the pulse are produced, each frequency shifted by a different amount.
0
Input pulse
E(t)
SHG Lens crystal Filter
Slow detector
2
Developed by J-C Diels
Diels and Rudolph, Ultrashort Laser Pulse Phenomena, Academic Press, 1996.
Mirror
By guruntech
超短脉冲的测量Ⅰ：自相关法
Outlines
Intensity Autocorrelation Single-shot autocorrelation Third-order Autocorrelation
Intensity Cross-Correlation
Interferometric Autocorrelation
Beamsplitter E(t–)
E(t ) E (t )
(2)
[ E(t) E(t )]
Delay
Mirror New terms
IA ( )


[E (t ) E (t )]
2 2
dt

IA ( )
(2)


E (t ) E (t ) 2 E(t )E(t ) dt
Mirrors
E(t–) Delay
Lens ES H(t, ) E(t)E(t ) IS H(t, ) I (t) I(t )
The Intensity Autocorrelation:
A(2) ( )


I (t )I (t ) dt

干涉自相关器
2 2
2
Usual Autocorrelation term

Also called the “Fringe-Resolved Autocorrelation”
超短脉冲测量Ⅱ：频率分辨光开关法
Outlines:
The Musical Score and the Spectrogram
Frequency-Resolved Optical Gating (FROG)
Baltuska, Pshenichnikov, and Weirsma, J. Quant. Electron., 35, 459 (1999).
超短脉冲测量Ⅲ： SPIDER
Outlines:
What is SPIDER?
How SPIDER works?
SPIDER apparatus X-SPIDER
强度自相关器
Crossing beams in an SHG crystal, varying the delay between them, and measuring the second-harmonic (SH) pulse energy vs. delay yields the Intensity Autocorrelation:
Input pulse Mirror Beam-splitter E(t) Aperture eliminates input pulses and also any SH created by the individual input beams. SHG crystal Slow detector Vd et( ) A (2) ( )