Key Characteristics & Real-Life Applications of LASERs
A laser is a device that stimulates atoms or molecules to emit light at particular wavelengths. In a laser, this emitted light is amplified to produce a very narrow, intense, and highly directional beam. Unlike ordinary light, the radiation from a laser typically covers an extremely limited range of visible, infrared, or ultraviolet wavelengths.
Lasers work based on the physical principle that excited atoms or molecules, when triggered, can emit photons—particles of light—of the same energy. Each photon then stimulates the emission of further photons in the same direction and phase, resulting in an amplified, coherent light beam.
Principle of Laser Operation
The core concept behind a laser is "stimulated emission". When an atom or molecule in an excited state encounters a photon with energy equal to the difference between its current and lower energy states, it can be stimulated to drop to the lower state, releasing a second photon. The new photon has the same energy, phase, and direction as the first.
This process leads to "amplification" of light. Energy is introduced into the system (often by electrical or optical means) to excite the atoms, causing a condition known as "population inversion"—where more particles exist in excited states than in lower ones, enabling continuous stimulated emission.
Characteristics of Laser Light
Laser light differs from normal light in several key ways:
- Monochromatic: Laser emits light of a single wavelength.
- Coherent: Photons move in phase, producing uniform waves.
- Directional: The beam is highly focused and travels in one direction with minimal divergence.
- High Intensity: The energy is concentrated in a small region, making the beam very intense.
These features make lasers valuable for precise applications across science, industry, and technology.
Key Formulas in Laser Physics
A few important formulas help understand and solve laser-based problems.
| Formula Name | Formula | Explanation |
|---|---|---|
| Energy of a Photon | E = hν = hc/λ | Relates the energy (E) of a single photon to its frequency (ν) or wavelength (λ), where h is Planck’s constant and c is the speed of light. |
| Laser Intensity | Intensity = Power / Area | Describes the laser’s power spread over its cross-sectional area. |
| Photon Emission Rate | Number/sec = Power / Energy per photon | Calculates how many photons are emitted each second at a given power. |
Example Problem: Calculating Number of Photons Emitted
Suppose a laser emits light at a wavelength of 600 nm with a power of 1 mW.
- First, calculate energy per photon:
E = hc/λ
= (6.626 × 10-34 J·s × 3 × 108 m/s) / (600 × 10-9 m)
≈ 3.31 × 10-19 J - Number of photons per second:
= Power / Energy per photon
= (1 × 10-3 J/s) / (3.31 × 10-19 J)
≈ 3.02 × 1015 photons per second
This calculation shows the massive number of photons even a low-power laser emits every second.
Comparison: Laser Light vs. Ordinary Light
| Property | Laser Light | Ordinary Light |
|---|---|---|
| Wavelength Range | Extremely limited (nearly single wavelength) | Broad range of wavelengths |
| Coherence | Highly coherent (waves are in phase) | Incoherent (random phase) |
| Directionality | Highly directional (narrow beam) | Spreads in all directions |
| Intensity | Very high | Low |
Step-by-Step Approach to Solving Laser Problems
- Identify the property or parameter to find (energy, intensity, number of photons).
- Select the appropriate formula based on given values (wavelength, power, area).
- Convert all quantities to SI units (e.g., nm to m, mW to W).
- Substitute the values carefully and solve stepwise, checking units at each step.
- Interpret the result, explaining its significance in contexts like intensity or emission rate.
Applications of Lasers
- Industrial: Used for cutting, welding, and engraving due to high precision.
- Medicine: Applied in surgeries (such as eye surgery) where focus and intensity are critical.
- Scientific Research: Essential in spectroscopy for analyzing material properties.
- Technology: Used in barcode scanners, communication systems, and optical data storage devices.
Types of Lasers
Lasers are categorized based on the material used as the medium for stimulated emission. They may employ gases, liquids, or solids to generate the laser beam, and each type is designed for specific uses depending on the desired wavelength and power.
Key Takeaways
- Lasers generate intense, highly directional, monochromatic, and coherent beams of light.
- They operate by stimulating emission from excited atoms or molecules and amplifying the resulting radiation.
- Their unique characteristics make them essential in many scientific, industrial, and technical fields.
For more on laser physics, stepwise practice questions, and guided resources, visit Vedantu's Laser Physics page.
To deepen your understanding, practice applying formulas and solving questions involving laser beams, energy calculations, and emission rates. Consistent practice will strengthen concept clarity and boost problem-solving speed.
FAQs on LASER in Physics: Meaning, Properties, and Uses
1. What does laser stand for?
Laser stands for Light Amplification by Stimulated Emission of Radiation. It describes a process where light is amplified due to the stimulated emission of photons, producing a highly focused and intense beam of light.
2. How does a laser work?
A laser works based on the principle of stimulated emission. The basic steps in laser operation are:
- Population inversion: More atoms are excited to a higher energy state than remain in the lower state.
- Stimulated emission: An incoming photon causes excited atoms to emit identical photons.
- Amplification: The process amplifies the light intensity through multiple reflections within the laser cavity, resulting in a strong, coherent, and directional laser beam.
3. What are the four main characteristics of laser light?
The four main characteristics of laser light are:
- Monochromaticity: Laser light consists of a single wavelength (color).
- Coherence: The light waves are in phase in time and space.
- Directionality: Laser beams are highly directional and travel in a straight, narrow path.
- High Intensity: Laser light has much higher intensity than ordinary sources.
4. What is stimulated emission?
Stimulated emission is a process where an incoming photon causes an excited atom to drop to a lower energy level, releasing a second photon with the same energy, phase, and direction as the first. This phenomenon is fundamental to laser operation and enables the amplification of light.
5. State the difference between ordinary light and laser light.
Laser light is highly monochromatic, coherent, intense, and directional, while ordinary light (from sources like bulbs) is polychromatic, incoherent, less intense, and spreads in all directions. These differences make lasers suitable for specialized applications in science, medicine, and industry.
6. What are the uses of lasers?
Lasers have a wide range of applications:
- Medical: Eye surgeries, skin treatments, tissue cutting
- Industrial: Cutting, welding, engraving
- Communication: Optical fiber transmission, bar-code scanning
- Research: Spectroscopy, holography
- Defense: Rangefinding, military targeting
7. Explain the term population inversion in the context of lasers.
Population inversion occurs when more atoms or molecules are in an excited energy state than in the lower energy state. This non-equilibrium condition is essential for stimulated emission to dominate over absorption, enabling the amplification of light in a laser.
8. What is the energy of a photon in a laser beam?
The energy of a photon in a laser beam is given by the formula:
E = hν = hc/λ,
where:
- E is the energy of the photon
- h is Planck's constant (6.626 × 10-34 J·s)
- ν is frequency, c is speed of light (3 × 108 m/s), and λ is wavelength
9. How is the intensity of a laser beam calculated?
The intensity of a laser beam is calculated by the formula:
I = Power / Area
where Power is the output of the laser (in watts) and Area is the cross-sectional area of the beam. Intensity is measured in watts per square meter (W/m2).
10. What are the different types of lasers?
Lasers can be classified based on the active medium:
- Solid-state lasers: e.g., Ruby laser
- Gas lasers: e.g., Helium-Neon laser
- Semiconductor (diode) lasers
- Dye lasers
- Fiber lasers
11. Why is laser light important in communication systems?
Laser light is vital in communication systems due to its high directionality, coherence, and intensity. These properties allow lasers to transmit large amounts of data over long distances through optical fibers with minimal loss and interference, making them essential for modern telecommunication and internet infrastructure.
12. Give a numerical example: How many photons per second are emitted by a 5 mW laser emitting at 500 nm?
Solution:
- Energy per photon: E = hc/λ = (6.626×10-34 × 3×108) / (500×10-9) = 3.98 × 10-19 J
- Power, P = 5 mW = 5×10-3 J/s
- No. of photons/sec = Power / Energy per photon
= (5×10-3) / (3.98×10-19) ≈ 1.26×1016 photons per second
