• Không có kết quả nào được tìm thấy

High Energy and Short Pulse Lasers

N/A
N/A
Nguyễn Gia Hào

Academic year: 2023

Chia sẻ "High Energy and Short Pulse Lasers"

Copied!
228
0
0

Loading.... (view fulltext now)

Văn bản

Inquiries about the use of the book should be directed to INTECH rights and permissions department (permissions@intechopen.com). The main task of this book is to expand the knowledge of the readers in both these sepa‐.

Generation of High-Intensity Laser Pulses and their Applications

Generation of ultrashort laser pulses

  • Short pulse generation by locking phase of longitudinal mode
  • How to lock phases of longitudinal modes
  • Dispersion

As the pulse duration of a laser pulse decreases, the pulse spectrum becomes wider and the pulse encounters the scattering effect in the medium. The absorption of the material is assumed to be recovered instantaneously in the rapidly saturating absorber (see Figure 2(c)).

Figure 1. Power at free running and mode-locked operations. When the phase relation is random among longitudinal modes, the intensity has fluctuation because of the beating among modes (left)
Figure 1. Power at free running and mode-locked operations. When the phase relation is random among longitudinal modes, the intensity has fluctuation because of the beating among modes (left)

Amplification of ultrashort laser pulses

  • Stretching of an ultrashort laser pulse before amplification
  • Rate equation
  • Energy amplification

Using the Frantz-Nodvik equation [12], the output energy of a laser pulse at the ith round trip in the amplifier can be expressed by A spontaneous emission traveling in the transverse direction of the gain medium has energy gain before the arrival of the laser pulse.

Figure 6. Parallel grating pulse stretching scheme. The parallel grating pulse stretcher introduces a negative GDD to the laser pulse.
Figure 6. Parallel grating pulse stretching scheme. The parallel grating pulse stretcher introduces a negative GDD to the laser pulse.

Focusing ultrashort laser pulses

  • Modeling of focusing scheme with low f-number parabolic mirror
  • Coherent superposition of monochromatic fields for femtosecond focal spot
  • Intensity distribution in the focal plane and its vicinity

The wavefront aberration of a laser pulse is one of the factors that determines the intensity distribution of a focal spot. Figure 15(b) shows the change of a focal point for an aberrated laser pulse as the f-number decreases.

Figure 12. On-axis focusing scheme for an aberrated laser beam with a low f-number parabolic mirror.
Figure 12. On-axis focusing scheme for an aberrated laser beam with a low f-number parabolic mirror.

Interaction of an intense laser pulse with plasma

As shown in the previous section, relativistic intensity is easily achieved by focusing a high-power femtosecond laser pulse. When a high-power laser pulse is focused on a thin metal target, the target immediately turns into a plasma, and electrons in the plasma are accelerated toward the direction of propagation of the laser beam by the ponderomotive force.

Conclusion

As the laser intensity increases, the proton energy distribution can be narrowed by a narrow electron energy distribution due to the radiation pressure. High-brightness, high-energy photons (X-rays and γ-rays) can also be produced by a laser-plasma accelerator.

Author details

As the intensity obtainable with the high-power laser pulse increases beyond 1024 W/cm2, some of the fundamental physical processes can be investigated. Since the invention of laser, the application field of laser has been expanded dramatically as the laser intensity increases.

Multi-GeV electron beams from subpetawatt laser pulses guided by capillary discharge in the self-trap regime. Beams of electrons, photons and ions from the relativistic interaction of petawatt laser pulses with solid targets.

High-Power Diode-Pumped Short Pulse Lasers Based on Yb:KGW Crystals for Industrial Applications

  • Introduction
  • Design of high-average power Yb:KGW laser system
    • Mode-locked Yb:KYW oscillator
    • Stretcher-compressor
    • Spectral shaping
    • Double-slab laser and amplifier
  • Performance of the Yb:KGW femtosecond laser system
  • Microhole drilling for processing drawing dies using ultrafast Yb:KGW laser

The position of the laser crystal can be determined by the displacement x from the center of the beam caustic in the cavity. The laser performance in CW mode is shown in Figure 5 for two cases of (a) Np polarization crystal with 4% output coupler and (b) Nm polarization crystal with 6%.

Figure 1. Schematic layout of the femtosecond laser system [15]. FM is a high reflective flat mirror; CM1 is a curved mirror with ROC = 400 mm; CM2 is a curved mirror with ROC = 600 mm; DM is a flat dichroic mirror; FL is a focusing lens; CL is a collimati
Figure 1. Schematic layout of the femtosecond laser system [15]. FM is a high reflective flat mirror; CM1 is a curved mirror with ROC = 400 mm; CM2 is a curved mirror with ROC = 600 mm; DM is a flat dichroic mirror; FL is a focusing lens; CL is a collimati

Acknowledgements

Optimization of the laser resonator increased the output power from 18 to 24 W in the case of Q-switched oscillator and from 17 to 21 W in the case of regenerative amplifier. This level of output power and quality of a laser beam is practically the same as the output power of Yb:KGW/Yb:KYW thin-disk lasers with medium level of output power [6, 9].

Yb:YAG-Pumped, Few-Cycle Optical Parametric Amplifiers

  • Recycling the pump energy
    • System description
  • Controlling the deposition of pump energy
    • Theoretical analysis
    • Experimental setup
  • Gain bandwidth engineering
  • Summary
  • Outlook

In the next OPCPA stage, the amplification is shifted to the second half of the seed spectrum and gains 6 W of the total amplification (Figure 6(a), pink curve). a) The experimental demonstration of Design 2. This similarity in the conversion efficiency is due to the fact that the spatiotemporal quality of the residual pump pulses after one amplifi‐. The feasibility of increasing the conversion efficiency of the system by reusing the pump energy after each amplification stage, in subsequent OPCPA stages, was demon-.

Figure 1. (a) Qualitative behavior of OPCPA amplified energy over the length of the nonlinear medium
Figure 1. (a) Qualitative behavior of OPCPA amplified energy over the length of the nonlinear medium

Laser-produced Soft X-Ray Sources

Tünnermann, "Octave-spanning OPCPA system delivering CEP-stable single-cycle pulses and 22 W average power at 1 MHz repetition rate", Opt. Krausz, “Investigating temporal compression of few-cycle pulses from an ultra-wideband, multi-mJ optical parametric amplifier,” in “Conf. Schultze, “Waveform-driven near-single-cycle milli-joule laser pulses generate sub-10 nm extreme ultraviolet continua,” Opt.

Brilliance Improvement of a Laser-Produced Soft X-Ray Plasma

Physical properties of a plasma

In competition with the heating processes, deionization takes place in the form of diffusion and recombination [27]. In addition to the thermal electrons, a suprathermal component is introduced, which is raised by nonlinear interactions such as resonant absorption. The resulting photon energy corresponds to the transition energy of the electron as described by Moseley's law, which is an extension of the Rydberg formula [30].

Gas dynamics of jet targets

Here, it is sufficient to take into account the change in the initial density ρ and the Mach number M in the case of a normal shock with respect to the flow direction. Internal shock waves and the Mach disk spatially limit the influence of the background gas. In the continuous regime, the extent of the shock structure changes with the nozzle pressure ratio p0/pb.

Figure 3. State functions of a flow in a de Laval nozzle: density ρ in terms of its stagnation value ρ 0 , Mach number M and the local cross-sectional area A reaching A *  at its throat position
Figure 3. State functions of a flow in a de Laval nozzle: density ρ in terms of its stagnation value ρ 0 , Mach number M and the local cross-sectional area A reaching A * at its throat position

The laser-produced soft X-ray source

Pinhole camera images of the plasma at a stagnation pressure of p0 = 11 bar for different background pressures pb as shown below the individual figure. The nozzle is opened for a period of 1 ms, generating an under-expanded supersonic jet that expands from stagnation pressure p0 = 11 bar in vacuum, i.e. the background pressure pb is as low as 10-4 mbar. In this way, areas are obtained with high densities of the target gas at relatively large distances from the nozzle.

Figure 7. Pinhole camera images of the plasma at a stagnation pressure of p 0  = 11 bar for various background pressures p b  as given below the individual figure
Figure 7. Pinhole camera images of the plasma at a stagnation pressure of p 0 = 11 bar for various background pressures p b as given below the individual figure

Gas jet and soft X-ray diagnostics

  • Schlieren imaging
  • Wavefront monitoring
  • Plasma characterization

The optical density distribution n(x, y, z) increases the optical path length, resulting in the wavefront deformation shown. The refractive index distribution in the z = 0 plane containing the jet axis is recovered from. The conversion of the refractive index n(x, y, 0) to a particle density N is done using the Lorentz-Lorenz formula [45].

Figure 10. Characteristic emission spectra of various target gases, captured with a soft X-ray spectrometer.
Figure 10. Characteristic emission spectra of various target gases, captured with a soft X-ray spectrometer.
  • Experimental results
    • Characterization of the target gas jet
    • Characterization of the plasma enhancement
  • Conclusion

Particle density before (Nmin) and after (Nmax) the walking shock, given on the symmetry axis of the jet. Consequently, this leads to a higher rarefaction of the gas and the typical spherical shock. This limits the size of the plasma in the beam direction and explains its smaller size.

Figure 13. Principle of plasma characterization by pinhole camera.
Figure 13. Principle of plasma characterization by pinhole camera.

High-Brightness Solid-State Lasers for Compact Short- Wavelength Sources

High repetition rate picosecond Yb:YAG thin disc-laser in LPP EUV source

The microlithography has been the central fabrication technology and continuous wavelength reduction is the main architecture. It is close to the high power plasma source, and its life extension is the most critical engineering concern. One of the laser beamlines is PERLA (Pearl) C, which aims to realize a compact, stable 500 W picosecond thin-disk laser with a repetition rate of 100 kHz [26].

Figure 1. Building of the HiLASE R&D Centre in Dolní Břežany, Czech Republic.
Figure 1. Building of the HiLASE R&D Centre in Dolní Břežany, Czech Republic.

High average power wavelength conversion of picosecond solid-state lasers

Several semiconductor cathodes were studied for higher efficiency to reduce the average power requirement of the driving laser in the repetition rate mode. Another consideration is the reduction of temporal microspikes in the SASE FEL pulses. This leads to local changes in the refractive index and results in the development of a thermal lens.

Figure 9. Left: Experimental setup of photocathode QE measurement. Right: Electron charge vs
Figure 9. Left: Experimental setup of photocathode QE measurement. Right: Electron charge vs

Cryogenic laser technology for high pulse energy picosecond amplifier

These pulses were compressed by a dielectric grating pair producing 1 J, 5 ps FWHM duration pulses at 100 Hz repetition rate." The repetition rate was recently increased to 500 Hz and the picosecond pulse energy is 1 J, and the resulting average. The dominant reason of the aberration was found to be the thermal lensing in the experimental condition as 6.3 kW/cm2 pump intensity and pump repetition rate of 100 Hz. This consists of Yb:YAG ceramic sheets in the laser head, dichroic beam splitters (DBSs), lens arrays (LAs), vacuum spatial filters (VSFs), and homogenized pump diode laser modules (PDs).

Figure 15. LEFT: Experimental configuration of the aberration measurement. FLD1, fiber-coupled pump diode at 936.6 nm; FLD2, fiber-coupled probe beam laser diode at 1065 nm; GT, Galilean telescope; W, windows; M, turning mirrors;
Figure 15. LEFT: Experimental configuration of the aberration measurement. FLD1, fiber-coupled pump diode at 936.6 nm; FLD2, fiber-coupled probe beam laser diode at 1065 nm; GT, Galilean telescope; W, windows; M, turning mirrors;

Large-scale High-power Laser Systems

2016) "Photothermal Method for Absorption Measurements in Anisotropic Crystals," Rev. 2011) "Development of a laser pulse storage technology. que in an optical super-cavity for a compact X-ray source based on laser-Compton scattering," Nucl. 2016) "Time-Resolved Measurement of Thermally Induced Deflections in a Cryogenically Cooled Yb:YAG Sheet Using a Wavefront Sensor." 2013) “Optimization of Wavefront Distortions and Thermal Stress-Induced Birefringence in a Cryogenically Cooled Multislab Laser Amplifier,” IEEE J. 2012) “Modeling of Enhanced Spontaneous Emission, Heat Deposition and Energy Extraction in Cryogenic-.

Multiterawatt Hybrid (Solid/Gas) Femtosecond Systems in the Visible

Photochemical lasers

  • XeF(C‐A) active medium
  • Xe 2 Cl active medium
  • Kr 2 F active medium

The breakthrough results obtained in the course of the iodine photodissociation laser development have stimulated extensive studies of the potential of the gaseous active media optical pump. The C state, which lies lower than the B state, is populated due to collisional relaxation of the latter in the presence of a buffer gas. Broad gain bandwidth on the C-A transition (Δλ . = 70 nm [21]) is accounted for by the repulsive nature of the A state.

Table 1. Characteristics of broadband active media.
Table 1. Characteristics of broadband active media.

Hybrid systems with XeF(C‐A) amplifiers

  • Hybrid systems based on surface discharge‐driven XeF(C–A) amplifiers
  • Hybrid systems based on XeF(C‐A) amplifiers pumped by the VUV radiation of e‐beam converter

Photos of the front end and the XeF(C‐A) amplifier incorporated in the THL‐30 hybrid system are shown in Figure 4. Schematic cross‐sectional diagram of the XeF(C‐A) amplifier: (1) vacuum diode, (2) beam converter, and (3) photolytic laser. The active medium of the XeF(C‐A) amplifier is created under the action of VUV radiation at a wavelength of 172 nm.

Figure 3. Photographs of the XeF(C‐A) amplifiers built at (a) LP3 and (b) LPI. (c) Inside view of the amplifier cell with multichannel surface discharges fired along its side walls.
Figure 3. Photographs of the XeF(C‐A) amplifiers built at (a) LP3 and (b) LPI. (c) Inside view of the amplifier cell with multichannel surface discharges fired along its side walls.

Wavelength scaling of laser‐matter interaction

  • Laser wake‐field acceleration
  • High‐order harmonic generation
  • Soft X‐ray lasers

Amplification of a chirped pulse in the XeF(C-A) amplifier was performed using the laser mixture containing 0.2 Torr XeF2 and 0.5 bar nitrogen at U0 = 95 kV. Wavelength scaling of the same form, but with α = 5 independent of laser intensity, was argued with the use of 1D-PIC code in the previous paper by Gibbon [70]. One of the biggest challenges is high-resolution 3D holographic microscopy of a wide variety of biological objects in the living state.

Conclusions

The laser plasma enables the generation of lasing in the soft X-ray region with beam performances close to those of XFELs [72]. In the case of the Xe2Cl active medium, repetition rates up to 10 Hz appear to be achievable with proper engineering. Stimulated emission due to the B(1/2)–X2Σ+ transition in the XeF molecule formed by the photodissociation of XeF2.

Nuclear-Induced Plasmas of Gas Mixtures and Nuclear- Pumped Lasers

Methods and sources of gas excitation by nuclear reaction products

  • Basic processes of formation and relaxation of nuclear-induced plasmas of gas mixtures Currently, direct nuclear pumping is implemented in gas media in which the populating of
  • Kinetics of plasma processes at nuclear pumping of gas mixtures
  • Design and development of experimental methods for nuclear-induced plasma research Pulsed nuclear reactors were used as a source of neutron radiation for NPLs research [3, 27,

This follows from calculations in that the electron energy distribution and energy formation of electron-ion pair in the gas does not depend on the type of charged particles [24, 25]. Therefore, we consider the kinetics of processes in plasma in the example as a two-component mixture. The gas pressure in the cell is measured by capacitance diaphragm gauge mounted at the top of the chamber.

Figure 1. Electron energy distribution in the ionized gas. 1—primary electrons of source; 2—electrons of ionization cascade; 3—electrons in the inelastic excitation region; 4—thermal and subthreshold electrons.
Figure 1. Electron energy distribution in the ionized gas. 1—primary electrons of source; 2—electrons of ionization cascade; 3—electrons in the inelastic excitation region; 4—thermal and subthreshold electrons.

NPL active media on transitions of atoms and atomic ions

  • IR lasers operating on transitions of Xe, Kr, and Ar
  • Visible-range lasers operating on Ne atom transitions
  • Metal vapor lasers

The pumping of the electron beam produced laser action in a row of neon transitions of 3p–3s in the red spectral region [86] (see Figure 6). During the study of luminescence of He-Ne mixtures with quenching additives [30], we obtained results confirming the main conclusion in [79]: the main and clearly dominant channels of neon 3p levels population when pumping through a hard ionizer are the processes unrelated to dissociative molecular ion recombination of neon. Our works [36, 98] have shown that population of mercury atom 73S1 level occurs in the process of molecular ion dissociative recombination and not in direct or stepwise electron excitation.

Figure 6. Scheme of laser transitions in neon. The wavelengths of laser and resonant transitions are indicated in nm.
Figure 6. Scheme of laser transitions in neon. The wavelengths of laser and resonant transitions are indicated in nm.

NPL active media on molecular transitions

  • Lasers operating on first negative system of nitrogen and carbon monoxide
  • Excimer lasers operating on halides of inert gases
  • Radiation of heteronuclear ionic molecules of inert gases

In: Proceedings of the 4th International Conference "Physics of Nuclear Pump Lasers and Pulse Reactors". In: Proceedings of the professional conference "Physics of nuclear excited plasma and problems of lasers with nuclear pumping". Active medium kinetics of a nuclear pumping laser based on transitions in the cadmium atom.

Hình ảnh

Figure 6. Parallel grating pulse stretching scheme. The parallel grating pulse stretcher introduces a negative GDD to the laser pulse.
Figure 12. On-axis focusing scheme for an aberrated laser beam with a low f-number parabolic mirror.
Figure 13. Spectrum and spectral phase for calculating the femtosecond focal spot.
Figure 17. (a) Electron acceleration though the laser wake field. The laser pulse is focused onto the gas target
+7

Tài liệu tham khảo

Tài liệu liên quan

When the positively chirped single- photon-level laser pulse and negatively classical laser pulse simultaneously reach the PPLN waveguide chip, a blue-shifted frequency component of