The Application Of Femtosecond Lasers

Femtosecond lasers are "ultrashort pulsed light" generating devices that emit light for an ultra-short period of time of only about one gigabit of a second. Femto is the abbreviation of the international system of units femto (femto), 1 femtosecond = 1 × 10^-15 seconds. The so-called pulsed light is only in a moment to release light. The light-emitting time of the camera's flash is about 1 microsecond, so the ultra-short pulse of femtosecond light is only about one billionth of its time to release light. As we all know, the speed of light is 300,000 kilometers per second (7 and a half weeks around the earth in 1 second) unparalleled speed, but during 1 femtosecond even light is only 0.3 microns forward.
Usually, we use flash photography to be able to cut the instantaneous state of the moving object. Similarly, with a femtosecond laser flash, it is possible to see every fragment of a chemical reaction that is going on at a violent speed. For this reason, femtosecond lasers can be used to study the mystery of chemical reactions.
Chemical reactions in general take place after an intermediate state of high energy, the so-called "activated state". The existence of the activation state was predicted theoretically by the chemist Arrhenius in 1889, but it could not be observed directly because it existed in a very short time. However, its existence was directly demonstrated by a femtosecond laser in the late 1980s, and this is an example of a chemical reaction identified with a femtosecond laser. For example, the decomposition of a cyclopentanone molecule into carbon monoxide and two ethylene molecules in an activated state.
Nowadays, femtosecond lasers are also used in a wide range of fields such as physics, chemistry, life sciences, medicine, engineering, etc. In particular, light and electronics go hand in hand and are expected to open up all kinds of new possibilities in the field of communication or computers and energy. This is because the intensity of light can transmit a large amount of information from one place to another almost without loss, making optical communication further high-speed. In the field of nuclear physics, femtosecond lasers have made a huge impact. Because pulsed light has a very strong electric field, it is possible to accelerate electrons to near the speed of light in 1 femtosecond, and therefore can be used as a "gas pedal" to accelerate electrons.
Medical applications
As mentioned above, the world in femtoseconds is so frozen that even light cannot move very far, but even at this time scale, atoms and molecules in matter and electrons in circuits inside computer chips are still moving. If you use femtosecond pulses you can make it stop instantly and study what is happening. In addition to flashes that stop time, femtosecond lasers are capable of drilling microscopic holes in metal down to 200 nanometers (two-thousandths of a millimeter) in diameter. This means that the ultrashort pulses of light that are compressed and locked inside for a short period of time get an amazingly high output without additional damage to the surrounding area. Furthermore, the pulsed light from the femtosecond laser is capable of taking extremely fine stereo images of the subject. Stereoscopic photography is of great use in medical diagnosis, thus opening up a new field of research called optical interference tomography. This is the use of femtosecond lasers to take stereoscopic images of living tissue and cells. For example, a very short pulse of light is aimed at the skin, and the pulsed light is reflected on the surface of the skin, with some of the pulsed light being directed into the skin. The inside of the skin consists of many layers, and the pulsed light that is shot into the skin is bounced back as small pulses, and from the echoes of these shaped pulsed lights in the reflected light, it is possible to know the internal structure of the skin.
In addition, this technology has great utility in ophthalmology, where it is possible to take stereoscopic images of the retina deep inside the eye. Doctors are thus able to diagnose whether there is a problem with its tissues. This examination is not limited to the eyes, but if the laser is sent into the body with fiber optics, all the tissues of various organs in the body can be examined, and in the future it may even be possible to check whether they have become cancerous.
Achieve ultra-precise clock
Scientists believe that if a clock with a femtosecond laser is made using visible light, it will be able to measure time more precisely than an atomic clock and will serve as the world's most accurate clock in the coming years. If the clock is accurate, then it also greatly improves the accuracy of the GPS (Global Positioning System) used for car navigation.
Why can visible light make accurate clocks? All clocks and watches do not have a pendulum and gears for movement, through the swing of the pendulum with a precise frequency of vibration, so that the gears turn seconds, accurate clocks are no exception. Therefore, in order to create more accurate clocks, it is necessary to use a pendulum with a higher frequency of vibration. Quartz clocks (clocks with crystal oscillations instead of pendulums) are more accurate than pendulum clocks, and that is because quartz resonators oscillate more times per second.
The frequency of oscillation of the cesium atomic clock, which is now the standard of time, is about 9.2 gigahertz (the word head of the international unit giga, 1 gig = 10^9). Atomic clock is the use of cesium atoms inherent frequency of oscillation, with its oscillation frequency consistent with the microwave instead of the pendulum, its accuracy is tens of millions of years only 1 second difference. In contrast, visible light has an oscillation frequency 100,000 to 1 million times higher than the microwave oscillation frequency, that is, visible light can be used to create precision clocks with a million times higher accuracy than atomic clocks. Now the world's most accurate clock using visible light has been successfully built in the laboratory.
With the help of this precise clock it is possible to verify Einstein's theory of relativity. We will be such a precise clock in the laboratory, the other in the office downstairs, consider the possible situation, after one or two hours, the results as predicted by Einstein's theory of relativity, due to the two layers have different "gravitational field" between the two clocks no longer point to the same time, the clock downstairs than the clock upstairs The clock downstairs moves slower than the clock upstairs. With a more accurate clock, perhaps even the watch on the wrist and the ankle would not have the same time that day. We can simply experience the fascination of relativity with the help of accurate clocks.
Light slowing down technology
In 1999, Professor Rainer Howe of Hubbart University in the United States succeeded in slowing down light to 17 meters per second, a speed that a car could catch up with, and later to a speed that even a bicycle could catch up with. This experiment involves research at the forefront of physics, and in this paper only two keys to the success of the experiment are presented. One is the construction of a "cloud" of sodium atoms at extremely low temperatures close to absolute zero (-273.15°C), a special gas state known as a Bose-Einstein condensate. The other one is a laser (control laser) that regulates the frequency of vibrations and irradiates the cloud of sodium atoms with it, with the result that something incredible happens.
First of all, with the help of the control laser, the pulsed light was compressed in the cloud of atoms and slowed down to an extreme speed. Then the control laser is shone again, and the pulsed light is restored and comes out of the atomic cloud. The pulses that were compressed are then widened again and the speed is restored. The whole process of entering the pulsed light information into the atomic cloud is similar to reading, storing and resetting in a computer, so this technique is useful for the implementation of quantum computers.
From "femtosecond" to "attosecond" world
Femtoseconds are already beyond our imagination. Now we are venturing into the world of "attosecond" which is even shorter than femtosecond. A is the abbreviation of the International System of Units (SI) word atto. 1 attosecond = 1 x 10^-18 seconds = 1 thousandth of a femtosecond. An attosecond pulse cannot be made with visible light because shorter pulses must be made with shorter wavelengths of light. For example, if you want to create a pulse with red visible light, it is not possible to create a pulse with a shorter wavelength than that. Visible light is the limit of about 2 femtoseconds, and for this reason the attosecond pulses are made with shorter wavelengths of x-rays or gamma rays. It is not clear what can be found in the future using an attosecond x-ray pulse. For example, using an attosecond inter-flash to visualize a biomolecule, it is possible to observe its activity on a very short time scale and perhaps identify the structure of the biomolecule.