Lasers are used in a wide variety of products and technologies, and the variety is amazing. From CD players, dental drills, high-speed metal cutters to measurement systems, it seems that everything has a laser in its shadow, and they all need lasers. But what exactly is a laser? What is the difference between a laser beam and a flashlight beam?
NASA Langley Research Center
The optical damage threshold test device has three lasers: high-energy pulsed neodymium-yttrium aluminum
Garnet lasers, titanium-sapphire lasers and resonant He-ne lasers.
NASA Langley Research Center
The optical damage threshold test device has three lasers: high-energy pulsed neodymium-yttrium aluminum
Garnet lasers, titanium-sapphire lasers and resonant He-ne lasers.
There are only about 100 different atoms in the entire universe. Everything we see is made up of more than 100 atoms combined in an infinite number of ways. The way these atoms are arranged between each other determines whether the object formed is a glass of water, a piece of metal, or the foam in a soda bottle!
Atoms are in perpetual motion. They vibrate, move, and rotate constantly, and even the atoms that make up our seats are in constant motion. Solids are actually moving! Atoms have several different excitation states, in other words, they have different energies. If enough energy is given to an atom, it can rise from the ground state energy level to the excited state energy level. The level of energy of the excited state depends on how much energy is given to the atom in the form of heat, light, electricity, etc.
The following diagram illustrates the structure of atoms well:
The simplest atomic model
It's made up of an atomic nucleus and electrons orbiting around it.
It's made up of an atomic nucleus and electrons orbiting around it.
A simple atom consists of a nucleus (containing protons and neutrons) and a cloud of electrons. We can think of electrons in an electron cloud as traveling in a number of different orbits around the nucleus.
Even if we look at atoms with modern technology, we cannot see the discrete orbitals of electrons, but it helps to think of these orbitals as the different energy levels of atoms. In other words, if we heat an atom, some electrons in low-energy orbitals may be excited to jump into higher-energy orbitals farther away from the nucleus.
Energy absorption:
Atoms can absorb energy in the form of heat, light, electricity, etc. The electron can then jump from a low energy orbital to a high energy orbital.
Although this description is simple, it does reveal the core principle of how atoms form lasers.
After the electron transition to a higher energy orbit, it will eventually return to the ground state. During this process, electrons release energy in the form of photons (a type of light particle). You'll see that atoms are constantly giving off energy in the form of photons. For example, the heating element in an oven turns bright red, where the red color is the red photon released by atoms excited by heat. When you look at the image on the TV screen, what you see is a variety of different colors of light emitted by phosphorus atoms excited by high-speed electrons. Any luminous object, including fluorescent lamps, gas lamps, and incandescent lamps, emits light by changing the orbits of electrons and releasing photons.
A laser is a device that controls the release of photons from excited atoms. “ Laser” light amplification by stimulated emission of radiation (light amplification by stimulated emission of radiation). This name briefly describes how the laser works.
Although there are many types of lasers, they all have some basic characteristics. In a laser, the laser medium must be pumped to make the atoms in an excited state. In general, a high-intensity flash or discharge can pump the medium, which in turn produces a large number of atoms (atoms containing high-energy electrons) in an excited state. In order for a laser to operate effectively, it must have a large number of atoms in an excited state. In general, atoms must be excited to rise to two or three energy levels above the ground state. This increases the degree of population inversion. The population inversion is the number ratio between atoms in the excited state and atoms in the ground state.
When the laser medium is pumped, it includes a number of atoms with excited electrons. The energy of the excited electron is higher than that of the lower level electron. Just as an electron can absorb a certain amount of energy to reach an excited state, an electron can also release that energy. As shown in the figure below, as long as the electron jumps to the lower level, it will release some of its energy. The released energy is converted into the form of photons (light energy). The emitted photon has a specific wavelength (color), depending on the energy state of the electron at the time of its release. Two atoms with the same electronic state emit photons of the same wavelength.
Laser light is very different from ordinary light. It has the following features:
The emitted laser is monochromatic. A laser contains light of a specific wavelength (that is, a specific color). The wavelength of light is determined by the energy released by the electrons as they return to a lower energy orbit.
The emitted laser has good coherence. The structure of the laser is better, and each photon follows the other photon. That is, the wavefront of all the photons is exactly the same.
Laser has good directivity. Laser beams are compact, focused and extremely energetic. On the contrary, the light emitted by the flashlight is scattered in multiple directions, and the light energy is weak and the concentration is low.
In order to achieve these three properties, a process called stimulated emission is required. This phenomenon cannot be seen in a normal flashlight because its atoms emit photons at random. In stimulated emission, atoms emit photons in an organized manner.
The photon emitted by the atom has a specific wavelength, which depends on the energy difference between the excited state and the ground state. If a photon (with a certain energy and phase) touches another atom that has an electron in the same excited state, stimulated emission can be caused. The first photon can excite or guide the atom to emit a photon, and the emitted photon (that is, the photon emitted by the second atom) oscillates in the same frequency and direction as the incoming photon.
Another key component of the laser is a pair of mirrors, located at each end of the laser medium. Photons of a specific wavelength and phase travel back and forth between the laser medium through the reflection of the reflectors at both ends. In doing so, they will excite more electrons to jump from high-energy to low-energy orbits, which will emit more photons of the same wavelength and phase, which will subsequently produce “ Waterfall ” In turn, a large number of photons of the same wavelength and phase are rapidly gathered in the laser. The mirror at one end of the laser medium is “ Semi-reflection ” Coating, that is, it only reflects part of the light, while other light can penetrate. The light that passes through is a laser.
The ruby laser consists of a flash tube similar to a camera flash, a ruby rod, and two mirrors (one of which is a semi-reflective mirror). The ruby rod is the laser medium, and the flash tube is the pumping source.