Terawatt-class output lasers
and their principles
Quantum Physicist and Brain Scientist
Visiting Professor of Quantum Physics,
California Institute of Technology
IEEE-USA Fellow
American Physical Society-USA Fellow
PhD. & Dr. Kazuto Kamuro
AERI：Artificial Evolution Research Institute
Pasadena, California
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Terawatt-class ultra-high-power lasers are extremely powerful lasers capable of delivering laser pulses with power levels in the terawatt (1 trillion watts) range. These lasers have revolutionized scientific research, industrial applications, and advanced technologies. There are several types of terawatt-class ultra-high-power lasers, each based on different principles. Here are three commonly used types:
These lasers have a wide range of applications, including scientific research, industrial machining, and laser-driven particle acceleration. There are several types of terawatt-class lasers, each based on different principles. Here are three commonly used types:
(1) Ti: sapphire lasers:
A Ti: sapphire laser is a type of solid-state laser that utilizes a titanium-doped sapphire crystal as the gain medium. It is known for its ability to generate ultrafast laser pulses in the femtosecond range. The power and principle of a Ti: sapphire laser can be explained as follows:
Principle:
The principle of a Ti: sapphire laser is based on the principle of optical amplification in a solid-state gain medium. The gain medium is a crystal made of sapphire (Al₂O₃) that is doped with small amounts of titanium ions (Ti³⁺). The titanium ions replace some of the aluminum ions in the sapphire lattice, introducing energy levels that allow for optical transitions.
To initiate laser action, the Ti: sapphire crystal is pumped with a suitable pump source. The most common pump sources for Ti: sapphire lasers are high-power green lasers, such as frequency-doubled Nd: YAG or frequency-doubled Nd: YVO₄ lasers. The pump light is absorbed by the titanium ions, exciting them to higher energy levels.
The excited titanium ions can then undergo stimulated emission, where they transition back to lower energy levels and emit photons. These emitted photons undergo further amplification as they interact with other excited titanium ions, bouncing back and forth between two mirrors placed at the ends of the crystal. One mirror is partially reflective, allowing a portion of the photons to pass through as the laser output, while the other mirror is highly reflective, reflecting the photons back into the gain medium for further amplification.
Power:
Ti: sapphire lasers are capable of delivering high-power laser pulses, typically in the range of milliwatts to multiple watts. The power output of a Ti: sapphire laser depends on various factors, including the pump power, the efficiency of the pump source, and the design of the laser system.
One of the key advantages of Ti: sapphire lasers is their ability to generate ultrafast laser pulses. The Ti: sapphire crystal has a broad gain bandwidth, enabling the laser to produce pulses with extremely short durations in the femtosecond range (10^-15 seconds). The ultrafast pulses are achieved through the technique of mode-locking, where the laser cavity is designed to achieve a specific mode-locking condition. This leads to the production of a train of extremely short, high-energy laser pulses.
Ti: sapphire lasers have a wide wavelength tuning range, typically covering the visible and near-infrared spectrum. By adjusting the cavity design and the intracavity elements, the wavelength of the laser output can be tuned within the gain bandwidth of the Ti: sapphire crystal.
Ti: sapphire lasers find applications in various fields, including ultrafast spectroscopy, laser micromachining, nonlinear optics research, and medical applications. The combination of high-power, ultrafast pulses, and tunability makes Ti: sapphire lasers versatile tools for a wide range of scientific and industrial applications.
(2) Diode-pumped solid-state lasers (DPSSL):
A diode-pumped solid-state laser (DPSSL) is a type of laser that utilizes semiconductor diode lasers as the pump source to excite a solid-state gain medium. The power and principle of a diode-pumped solid-state laser can be explained as follows:
Principle:
The principle of a DPSSL involves the use of a solid-state gain medium, typically a crystal or glass doped with rare-earth ions, such as neodymium (Nd) or ytterbium (Yb). The gain medium is optically pumped by high-power semiconductor diode lasers, which emit light in the near-infrared spectrum.
The pump diode lasers generate high-intensity light, which is focused onto the gain medium. The pump light is absorbed by the rare-earth ions in the gain medium, exciting them to higher energy levels. These excited ions can then undergo stimulated emission, releasing photons of specific wavelengths as they transition back to lower energy levels.
Power:
Diode-pumped solid-state lasers can produce a wide range of power outputs, ranging from a few milliwatts to several kilowatts. The power output depends on various factors, including the pump power, the efficiency of the pump diode lasers, the characteristics of the gain medium, and the design of the laser system.
One of the main advantages of DPSSLs is their high pump efficiency. Semiconductor diode lasers have high electrical-to-optical conversion efficiencies, resulting in efficient use of electrical power for pumping the gain medium. This enables DPSSLs to achieve higher overall efficiency compared to other laser types.
The power output of a DPSSL can be further increased by employing amplification techniques such as Q-switching or mode-locking. In Q-switching, a rapid optical switch is used to store energy in the gain medium for a short time before releasing it in a high-energy pulse. Mode-locking, on the other hand, creates a train of ultra-short laser pulses by synchronizing the emission of photons in the gain medium.
DPSSLs are widely used in various applications, including laser marking, material processing, scientific research, and medical treatments. They offer advantages such as compact size, high beam quality, long operational lifetime, and excellent wavelength flexibility. With advancements in diode technology and gain medium development, DPSSLs continue to be a versatile and efficient choice for many laser applications.
(3) Excimer lasers:
An excimer laser is a type of gas laser that produces high-energy laser light in the ultraviolet (UV) range. It operates on the principle of excited dimer molecules formed by a mixture of noble gases and halogen molecules. The power and principle of an excimer laser can be described as follows:
Principle:
The principle of an excimer laser is based on the concept of an excimer, which is an excited dimer molecule. The laser medium consists of a mixture of noble gases, such as argon (Ar), krypton (Kr), or xenon (Xe), and a halogen gas, typically fluorine (F) or chlorine (Cl). These gases are placed in a discharge tube and excited by an electrical discharge or by a pulsed electric discharge.
When the discharge is initiated, an electron collides with a noble gas atom, causing it to become excited. The excited noble gas atom then transfers its energy to a halogen molecule, forming a temporary excited-state dimer molecule known as an excimer. This excimer is in a metastable state and exists only for a short duration, typically on the order of nanoseconds (10^-9 seconds).
During the brief lifetime of the excimer, it releases its excess energy in the form of laser light. The laser emission occurs when the excimer spontaneously decays and returns to its ground state. This emission is highly energetic and occurs in the UV range, often in the deep UV region.
Power:
Excimer lasers are capable of delivering high-power laser beams, typically in the range of kilowatts to multi-kilowatts. The power output of an excimer laser depends on various factors, including the gas mixture, the discharge parameters, and the optical design of the laser system.
To increase the power output, excimer lasers employ amplification techniques such as pulse amplification or beam multiplexing. In pulse amplification, the initial laser pulse generated by the excimer is amplified by passing it through multiple amplification stages, often using a technique called optical pumping. This process involves pumping the laser beam through a chain of amplifiers, each increasing the power of the pulse.
Excimer lasers find applications in various fields, including industrial processes, scientific research, and medical treatments. They are commonly used in laser lithography for microchip fabrication, eye surgery for vision correction (LASIK), and the production of high-resolution printing plates. The high-power and short-pulse characteristics of excimer lasers make them suitable for precision material removal, photoablation, and photochemical reactions where a controlled and intense UV light source is required.
(4) Free electron lasers:
Free Electron Lasers (FELs) are a different class of terawatt-class lasers that operate on the principle of relativistic electron acceleration. FELs utilize a beam of high-energy electrons that are accelerated to near the speed of light using particle accelerators. These high-speed electrons are then passed through an undulator, which consists of alternating magnetic poles. As the electrons pass through the undulator, they undergo sinusoidal motion due to the magnetic field, leading to the emission of intense, coherent laser light through the process of stimulated emission. FELs can generate terawatt-class outputs across a wide range of wavelengths, including X-rays and infrared.
Free electron laser (FEL) is a type of laser that utilizes a beam of high-energy electrons to generate coherent and intense laser light across a wide range of wavelengths, including X-rays and infrared. Unlike conventional lasers that rely on fixed atomic or molecular transitions, FELs exploit the properties of relativistic electrons moving through a periodic magnetic field. The power and principle of an FEL are as follows:
Principle:
The principle of an FEL is based on the phenomenon of self-amplified spontaneous emission (SASE). It begins with a beam of high-energy electrons that are accelerated to nearly the speed of light using a particle accelerator, such as a linear accelerator (linac). The accelerated electrons are then directed into a long undulator, which consists of a series of alternating magnetic poles.
As the high-speed electrons pass through the undulator, they undergo a sinusoidal motion due to the alternating magnetic field. This motion causes the electrons to emit radiation in the form of spontaneous emission, producing a broad spectrum of incoherent light. However, the undulator is carefully designed such that the emitted light interacts with the passing electrons and induces further amplification through stimulated emission.
Power:
The power of a free electron laser can be exceptionally high, ranging from gigawatts to even terawatts. This high power is achieved through the interaction between the emitted radiation and the electron beam. As the electrons travel through the undulator, the radiation produced in one section of the undulator can stimulate further emission and amplification in subsequent sections.
The amplification process in an FEL is based on the synchronization of the electron bunches with the emitted radiation. By carefully controlling the energy, density, and phase of the electron beam, the FEL can achieve coherence and build-up of the laser light intensity over a long distance. This process leads to the production of an intense, highly coherent, and tunable laser beam.
Due to the unique principles of FELs, they have significant advantages over conventional lasers. FELs can generate laser light across a broad range of wavelengths, including X-rays, which are challenging to produce with other laser technologies. They also offer excellent tunability, allowing researchers to select specific wavelengths by adjusting the energy and trajectory of the electron beam. This makes FELs valuable tools for a wide range of applications, including materials science, imaging, spectroscopy, and advanced research in various scientific disciplines.
(5) Chirped Pulse Amplification (CPA) Lasers:
Chirped Pulse Amplification is a technique that allows for the generation of ultrashort laser pulses with high peak powers. In CPA lasers, the laser pulse is first stretched in time using a dispersive element such as a pair of diffraction gratings. The stretched pulse is then amplified using an amplification medium, typically a solid-state laser or a gas laser. After amplification, the pulse is compressed in time using a compressor, which removes the chirp and restores the original short pulse duration. By repeating the amplification process in multiple stages, terawatt-class peak powers can be achieved.
Chirped Pulse Amplification (CPA) is a technique used to generate ultrashort, high-energy laser pulses. The power and principle of a CPA laser can be explained as follows:
Principle:
The principle of CPA is based on the manipulation of laser pulses in time domain and the amplification of these pulses in a controlled manner. The technique involves three main steps: stretching, amplification, and compression.
(a) Stretching: The initial laser pulse is stretched in time using a dispersive element, typically a pair of diffraction gratings. The pulse is dispersed in a way that different wavelengths of the pulse travel at slightly different speeds, causing the pulse to elongate in time. The stretching process increases the pulse duration while maintaining its energy.
(b) Amplification: The stretched pulse is then directed into an amplification medium, which can be a solid-state laser or a gas laser. The pulse interacts with the gain medium, where it undergoes amplification. The amplification is achieved by pumping energy into the gain medium, increasing the energy level of the pulse. The amplification process is usually performed in multiple stages to achieve higher energy levels.
(c) Compression: After amplification, the pulse is recompressed in time to its original duration. This is achieved by passing the amplified pulse through a compressor, which consists of another set of diffraction gratings or other dispersive elements. The compressor compensates for the initial stretching, causing the different wavelengths of the pulse to recombine and create a short, high-energy pulse. The recompression process reduces the pulse duration while preserving its energy.
Power:
CPA lasers are capable of delivering extremely high peak powers, including terawatt-class powers. The power output of a CPA laser depends on several factors, including the pump power, the efficiency of the amplification process, and the characteristics of the gain medium.
One of the main advantages of CPA lasers is the ability to generate ultrashort pulses with high energies. By stretching the pulse in the initial stage, the energy is spread over a longer duration, which allows for efficient amplification without damaging the gain medium. The subsequent compression process then concentrates the energy into a short pulse, resulting in high peak powers.
CPA lasers are widely used in various applications, including laser fusion, high-energy physics experiments, nonlinear optics research, and laser-driven particle acceleration. The technique has enabled significant advancements in laser science, allowing researchers to explore new frontiers in ultrafast phenomena and high-intensity laser-matter interactions.
(6) Optical Parametric Chirped Pulse Amplification (OPCPA) Lasers:
OPCPA is an extension of the CPA technique that utilizes nonlinear optical processes for amplification. In OPCPA lasers, a high-energy pump laser is used to generate an ultrashort seed pulse, typically in the near-infrared range. This seed pulse is then passed through a nonlinear crystal, where it interacts with a high-energy pump pulse. The interaction in the nonlinear crystal leads to parametric amplification of the seed pulse, resulting in significant amplification of the pulse energy. OPCPA lasers can achieve extremely high peak powers and are well-suited for generating terawatt-class output.
Optical Parametric Chirped Pulse Amplification (OPCPA) is an advanced technique used to generate high-energy, ultrashort laser pulses. It combines the principles of optical parametric amplification and chirped pulse amplification to achieve efficient and powerful laser outputs. The power and principle of an OPCPA laser can be explained as follows:
Principle:
The principle of OPCPA is based on the interaction of two laser pulses in a nonlinear optical crystal, typically a nonlinear crystal such as a periodically poled lithium niobate (PPLN) or a beta-barium borate (BBO) crystal. The technique involves three main steps: parametric amplification, chirped pulse amplification, and pulse compression.
Parametric Amplification: In OPCPA, a high-energy pump laser pulse and a low-energy seed laser pulse are combined in a nonlinear crystal. The nonlinear crystal has specific properties that allow for a process called parametric amplification. The pump laser pulse provides the energy, and the seed laser pulse provides the timing and spectral characteristics.
As the pump and seed pulses propagate through the nonlinear crystal, they interact through a nonlinear process called parametric amplification. This process involves the conversion of energy from the high-energy pump pulse to the low-energy seed pulse, resulting in the amplification of the seed pulse while depleting the pump pulse. The parametric amplification process allows for the transfer of energy and characteristics from the pump pulse to the seed pulse.
Chirped Pulse Amplification: The amplified seed pulse, which now carries the characteristics of the original pump pulse, is then directed into an amplification medium, such as a solid-state laser or a gas laser. Similar to the principle of Chirped Pulse Amplification (CPA), the pulse is further amplified through multiple stages to increase its energy while maintaining its duration.
Pulse Compression: After amplification, the pulse is recompressed to its original duration. This is achieved using a pulse compressor, typically employing dispersive elements such as diffraction gratings or prisms. The compressor compensates for the initial chirping or stretching of the pulse, causing different wavelengths to recombine and create a short, high-energy pulse. The recompression process reduces the pulse duration while preserving its energy.
Power:
OPCPA lasers are capable of delivering high-energy laser pulses with peak powers in the terawatt (1 trillion watts) range. The power output of an OPCPA laser depends on several factors, including the pump power, the efficiency of the parametric amplification process, and the characteristics of the amplification medium.
One of the main advantages of OPCPA lasers is their ability to achieve high peak powers with excellent pulse characteristics. The parametric amplification process allows for efficient energy transfer and the preservation of the spectral and temporal characteristics of the seed pulse. The subsequent chirped pulse amplification and pulse compression steps further enhance the power and duration of the laser pulse, resulting in high-energy, ultrashort pulses.
OPCPA lasers find applications in various fields, including high-intensity laser physics, attosecond science, and high-energy density physics. The technique enables researchers to explore extreme laser-matter interactions, nonlinear optics phenomena, and time-resolved spectroscopy at unprecedented power levels and temporal resolutions.
Advises from professor Kamuro
These terawatt-class ultra-high-power lasers have revolutionized various fields of research and technology. They enable studies in high-energy physics, ultrafast spectroscopy, laser-driven particle acceleration, materials science, and laser-based manufacturing, among others. The principles and capabilities of these lasers continue to advance, pushing the boundaries of what is possible in laser science and applications.
To achieve laser emission, the gain medium is placed between two mirrors, forming an optical cavity. One of the mirrors is partially reflective, allowing a portion of the emitted photons to pass through and form the laser output. The other mirror is highly reflective, bouncing the photons back into the gain medium for further amplification.
It's important to note that terawatt-class lasers require sophisticated optical systems, precise alignment, and advanced control techniques to achieve the desired performance. They play a crucial role in various fields of research and technology, enabling studies in high-energy physics, material science, and laser-based manufacturing, among others.
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Quantum Brain Chipset & Bio Processor (BioVLSI)
Prof. PhD. Dr. Kamuro
Quantum Physicist and Brain Scientist involved in Caltech & AERI Associate Professor and Brain Scientist in Artificial Evolution Research Institute（ AERI: https://www.aeri-japan.com/ ）
IEEE-USA Fellow
American Physical Society Fellow
PhD. & Dr. Kazuto Kamuro
email: info@aeri-japan.com
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【Keywords】 Artificial Evolution Research Institute：AERI
HP： https://www.aeri-japan.com/
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