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Ultrashort Visible Laser Pulses
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Book Description

This Spotlight discusses the generation of ultrashort pulses in three spectral regions: visible, deep-ultraviolet, and terahertz ranges. We explore a method to control the carrier-envelope phase (CEP) dynamics based on all-optical phase stabilization. The concepts presented here can be used to generate high-intensity, low-cycle laser optical fields with an exactly locked CEP. Such pulses are indispensable to the study of coherent x-ray and attosecond physics.

Book Details

Date Published: 11 December 2019
Pages: 73
ISBN:
Volume: SL54

Table of Contents
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1 Introduction
1.1 Importance of ultrafast phenomena research and its brief history
1.2 Ti:sapphire laser

2 Nonlinear Optical Processes and Nonlinear Susceptibilities
2.1 Optical-field-only-dependent nonlinearity
2.2 Intensity-dependent case

3 Optical Parametric Amplification

4 Noncollinear Optical Nonlinear Parametric Amplification
4.1 Basics of ultrashort pulse generation by NOPA
4.2 Broadband phase-matching condition in type-I BBO crystal
4.3 Type-I phase-matching condition in BBO crystal

5 Optical Parametric Fluorescence and Gain Spectra
5.1 Optical parametric fluorescence spectrum
5.2 Parametric gain spectrum

6 Configurations of NOPA and Ultrafast Spectroscopy Setups
6.1 Pulse-front-matching configuration in NOPA
6.2 Experimental setup of NOPA
6.3 Configuration of pump-probe experimental setup

7 Carrier-Envelope Phase-Controlled Visible Pulse
7.1 Carrier-envelope phase
7.2 CEP-stabilized NOPA
7.3 Chirp compensation by a prism pair
7.4 Multicolor CEP-locked pulse generation by a spatial filter
7.5 Double-color CEP-locked pulse generation by dual color seeding

8 Broadband Parametric Four-Wave Mixing for Ultrashort DUV Pulse Generation
8.1 Introduction
8.2 Principle of broadband chirped pulse four-wave mixing
8.3 Experimental
8.4 Results and discussion
8.5 Intermediate conclusion

9 Ultrafast Spectroscopy System
9.1 Multichannel lock-in detection for transient absorption spectroscopy
9.2 Photodetector-array-based time-resolved spectroscopy system
9.3 Fast-scan TA spectroscopy system
9.4 Fast-scan delay for TAS
     9.4.1 Fast-scan delay for femtosecond TAS
     9.4.2 Fast-scan delay for picosecond TAS
9.5 Spectrometer for TAS

10 Two-Dimensional Correlation Spectroscopy for Ultrafast Transient Absorption
10.1 Basic analysis scheme
10.2 Analytical expression for 2-D spectra
     10.2.1 Spectral bands with common decay rate
     10.2.2 Spectral bands with different decay rates
     10.2.3 Probe wavelength-dependent decay rate
     10.2.4 Spectral bandwidth narrowing with delay time

11 Conclusion

Preface

Photoreactions play important roles in daily life, as seen in light sensor proteins in the retina, photovoltaic materials in solar cells, photosynthesis in chlorophyll, etc. Ultrashort pulse lasers have enabled us to visualize the primary reaction mechanisms of those photoreactions. We discuss ultrashort pulse generation in two different spectral regions, i.e., (1) visible and (2) deep-ultraviolet (DUV) ranges and their applications for spectroscopy. The generation of ultrashort pulse utilizes various nonlinear optical (NLO) processes whose basis is described in Section 2. At first, we discuss one of the NLO processes, i.e., optical parametric amplification (OPA) in Section 3. Then we discuss sub-10-fs visible pulse generation from a noncollinear optical parametric amplifier (NOPA) utilizing various NLO processes. Compared with traditional optical parametric amplifiers (OPAs), this amplifier has the outstanding advantage of broad spectral bandwidth, which is essential to obtain an ultrashort pulse. The basic idea of NOPA is introduced in Section 4, and the principle and methodology to obtain gain bandwidth are discussed in Section 5. Several key techniques of the development of NOPA are described based on the research activities of our groups in the University of Tokyo, University of Electro-Communications, and National Chiao Tung University. Experimental details of NOPA are shown in Section 6 with its application to a pump-probe time-resolved experiment. The generated pulse from the NOPA was as short as 7 fs with the spectrum of 556 to 753 nm, which can elucidate ultrafast dynamics of photoreactions observing spectral dynamics with a 7-fs time-resolution in the pump–probe measurement. A multichannel lock-in amplifier was utilized in the pump–probe experiment to detect the broadband probe spectrum of the ultrashort laser pulse. In Section 7, we explore an approach toward the control of carrier-envelope dynamics, which is based on all-optical phase stabilization. We show that the use of fundamental properties of parametric interaction of light enables the carrier-envelope phase (CEP) of the idler pulse to be locked to a fixed value regardless of the carrier slip in the driving laser source. The concept presented and experimentally verified in this research can be implemented for generation of high-intensity few-cycle laser optical fields with exactly locked CEP. Such pulses are indispensable to the study of coherent x-ray and attosecond physics. Then sub-10-fs DUV pulse generation is discussed in Section 8. Broadband chirped-pulse four-wave mixing and a pulse compressor consisting of a prism pair and a grating pair are used to generate 9.7-fs DUV pulses. A large fraction of the dispersion up to 1000 fs2 is compensated without inducing third-order dispersion. The nearly-Fourier-transform-limited DUV pulse generated has a smooth spectral and temporal profile and is suited to DUV-pump ultrafast spectroscopy. Section 9 describes our application of ultrashort laser pulses to ultrafast transient absorption spectroscopy. Ultrafast spectral dynamics was observed by improving the signal-to-noise ratio using the multichannel lock-in detection system and photodetector array. Fast-scan delay has enabled us to study the ultrafast dynamics of photofragile materials such as protein samples, avoiding damage accumulation by the ultrashort laser pulse. The observed ultrafast dynamics were analyzed using two-dimensional correlation spectroscopy whose detailed description can be found in Section 10.

Takayoshi Kobayashi
Atsushi Yabushita
December 2019


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