The characteristics of laser mainly include

Laser is also light, which is not essentially different from ordinary light. But laser is a special kind of light. Compared with ordinary light, it has four characteristics: good directivity, good monochromaticity, high brightness and excellent coherence. All kinds of applications of laser are based on the above characteristics, and there is no second light source comparable to laser in these aspects.

(1) pointing thousands of miles away-a good direction.

Directivity is the directivity of light beam, which is often evaluated by the size of angle A. The smaller the angle A is, the smaller the beam divergence is and the better the directivity is. If the angle a tends to zero, it can be approximately called "parallel light". Ordinary light, such as lights and sunlight, is emitted in all directions, far from the direction. Although people can get approximate "parallel light" by placing the light source on the focus of a lens or concave mirror, because the light source always has a certain size, the divergence caused by aperture diffraction of the mirror always has a divergence angle of 0.0 1 radian (1 radian = 103 milliradian = 57.296 degrees), so the mirror cannot be absolutely accurate.

Due to the limitation of the resonant cavity on the oscillation direction of light, the laser beam can only oscillate and amplify along the cavity axis by stimulated radiation, so the laser beam has high directivity. Of course, due to the diffraction limit of the resonator mirror, it is quite difficult to make the divergence angle zero without taking some measures. Nevertheless, the divergence angle of laser is generally in the order of milliradian, which is more than 10 times smaller than searchlight and about 100 times smaller than microwave. With the help of optical emission system, the α angle of laser beam can be as small as almost zero, which is close to parallel beam.

(2) Red, orange, yellow, green, blue and purple-good monochromaticity.

From the electromagnetic spectrum, we can see that there is a wavelength corresponding to a color. "After the rain, the sun sets and the rainbow stands in the sky" is a common natural phenomenon, because sunlight contains all the wavelengths of visible light, that is, all the colors in the world, but it turns white. Therefore, "white" light is a mixture of red, orange, yellow, green, cyan, blue and purple light. The smaller the wavelength range of light, the purer its color and the brighter it looks. Usually we call this phenomenon high monochromaticity. Generally, a section of radiation whose wavelength range is less than a few angstroms (1 angstrom = 65438+ one billionth centimeter) is called monochromatic light, and the light source that emits monochromatic light is called monochromatic light source. Just as the divergence angle of laser beam is a sign to measure the directivity of beam, the width of spectral line is a standard to measure monochromaticity.

People have created many monochromatic light sources in long-term production and scientific experiments, such as neon lights, mercury lamps and sodium lamps. In the past, the best monochromatic light source was isotope krypton lamp 86. The wavelength range of light emitted at low temperature was only about 0.005 angstrom, and the spectral line width at room temperature was 0.0095 angstrom, so the color was very bright. The appearance of laser has caused a great leap in the monochromaticity of light. For example, the wavelength range of He-Ne laser with good monochromaticity is even less than one millionth of an angstrom, and the smallest has reached several millionths of an angstrom. Its monochromaticity is hundreds of millions of times that of ordinary light. Therefore, laser is the purest and freshest light.

(c) 654.38+000 billion times of sunlight-high brightness.

Simply put, brightness refers to the luminous intensity of a light source per unit area. It is an important index to evaluate the brightness of light source.

In order to meet the needs of production practice, it is optically stipulated that the light power emitted by a light source in a certain direction in a unit area is called the brightness of the light source in that direction. In general lighting engineering, the unit of brightness is "Xiti". Simply put, 1 Siti means that the luminous intensity is 1 candlelight in the unit area of 1 cm2. Please refer to the table for the brightness of several light sources.

As we all know, electric lamps are much brighter than candles, carbon arc lamps are brighter than electric lamps, and ultra-high pressure mercury lamps are more than ten times brighter than carbon arc lamps. So, what is the brightest light source in the world? With the appearance of artificial small sun (long arc xenon lamp), its brightness has caught up with the sun. High voltage pulsed xenon lamp is brighter than the sun 10 times. But in front of the laser, whether it is the sun, artificial small sun or high-voltage pulsed xenon lamp, their brightness is nothing. The brightness of He-Ne laser with power of only 1 MW is about 100 times higher than that of the sun. The brightness of the giant pulsed solid-state laser can be 10 10 times higher than the brightness of the sun surface, that is,10 billion times. What an amazing leap in the brightness of the light source this year! It is no exaggeration to say that laser is the brightest light source in modern times, and its brightness is beyond anything in the past. So far, only the intense flash of hydrogen bomb explosion can be compared with it. It should be noted here that the brightness of laser must not be misunderstood as the light energy that laser can give is more than that given by sunlight at the same time. In fact, this is because the pulse width is narrow and the beam divergence angle is small.

(d) Black and white stripes are clear and consistent.

Laser is a kind of coherent light, which is the most important difference between laser as a brand-new light source and ordinary light source. So, what is the coherence of light? We might as well explain it by water waves: when you throw two stones into a calm lake at the same time, they each form a set of water waves. Two groups of water waves propagate independently, but influence and interfere with each other, which is called "wave interference phenomenon". If we carefully observe the interference of two groups of water waves, we will further find that if the two groups of peaks meet, the waves will fluctuate higher; Similarly, if the trough meets the trough, the trough will also become deeper. If the peaks of one set of water waves meet the valleys of another set of water waves, the waves will cancel each other out. This phenomenon is called "wave superposition phenomenon". The superposition principle of waves is as follows: each wave independently excites vibration in the area where it arrives, regardless of whether other waves exist at the same time; When two waves interfere at the same time and act on a point, the vibration of the point is equal to the algebraic sum of the vibrations caused by each wave acting alone. We call two series of waves that can produce interference phenomena "interference waves". A wave source that emits coherent waves is called a "coherent wave source".

However, it should be pointed out that the above four characteristics are generally compared with ordinary light. In fact, there is no need to put forward high requirements for all four characteristics in practical application. For example, the main requirements of holography are good monochromaticity and coherence; The main requirements of laser communication are good directivity, monochromaticity and coherence; The main requirements of laser ranging are good directivity and high brightness; The main requirements of laser weapons are high brightness and good directivity. According to different application purposes, lasers with different characteristics should be selected or developed.