Unit 5 LASERS | Physical optics 1st Sem | Bachelor of Optometry

 

Unit 5 – LASERS: A Comprehensive Introduction

1. What Exactly Is a Laser?

The word LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. In plain language, a laser is a device that gathers energy inside an optical cavity and releases it as an extremely pure, coherent, and highly directional beam of light. Unlike the diffuse glow of a torch or the broad spectrum of a filament bulb, a laser’s output is razor-sharp in both wavelength and spatial spread. This singularity underpins its diverse applications—from precision eye surgery and fiber-optic communication to the atomic clocks that underpin the GPS in your phone.

2. A Brief Historical Perspective

The conceptual foundation of lasers dates back to Albert Einstein’s 1917 paper introducing the idea of stimulated emission. Yet it took more than four decades—and a healthy rivalry between physics labs—to turn those equations into a working device. In 1954, Charles H. Townes demonstrated the MASER (Microwave Amplification by Stimulated Emission of Radiation). Six years later, Theodore Maiman unveiled the first optical ruby laser at Hughes Research Laboratories. The breakthrough not only earned multiple Nobel Prizes but also ushered in the photonics era, fundamentally altering medicine, industry, and consumer electronics.

3. The Basic Principle: From Atoms to Amplified Light

Every laser—regardless of size, cost, or wavelength—relies on three core ingredients:

1. Active (Gain) Medium. Atoms, ions, or semiconductor junctions whose electronic energy levels can be selectively excited.
2. Population Inversion. A non-equilibrium state in which more particles occupy an excited level than the lower one, defying the Boltzmann distribution. Achieving and sustaining inversion is the laser engineer’s primary challenge.
3. Optical Resonator. Usually two parallel mirrors that trap photons, forcing them to bounce back and forth through the gain medium. One mirror is partially transparent, allowing a fraction of the amplified light to escape as the usable laser beam.

When an excited atom sees a photon whose energy matches the gap between its excited and ground states, it can be stimulated to emit a second photon in perfect phase, direction, and frequency with the first. This domino effect cascades inside the cavity, producing exponential amplification—hence the word Light Amplification.

Fig 1. Stimulated emission: the heart of all laser operation.

4. Key Properties That Make Lasers Special

Coherence—both temporal and spatial—is the defining trademark of a laser. All emitted photons march in lockstep like a perfectly drilled platoon, enabling interference over long distances. Monochromaticity restricts the emission to a linewidth as narrow as parts per billion. Finally, directionality produces a beam that diverges by mere milliradians, allowing power densities that can drill steel or write Blu-ray discs. Together, these traits give lasers an edge over ordinary light sources in precision applications ranging from LiDAR mapping to photorefractive keratectomy (PRK) in ophthalmology.

5. Safety Note

Laser beams can be deceptively invisible (infra-red) yet searingly powerful. Always check the IEC 60825-1 classification and use appropriate eyewear: Class 1 is safe under all conditions, while Class 4 can ignite materials and cause irreversible eye damage even from diffuse reflections.

6. Looking Ahead to Further Topics

With the foundational ideas in place, the subsequent lessons will dive deeper into:

• Population inversion techniques—optical, electrical, chemical, and nuclear pumping
• Detailed study of four seminal laser architectures: He-Ne, Nd:YAG, CO₂, and semiconductor diode lasers
• System design parameters—threshold gain, mode locking, Q-switching, beam quality (M²), and thermal management
• Cutting-edge applications from 3-D surface profiling to femtosecond ophthalmic surgery

Spontaneous vs Stimulated Emission – The Quantum Physics Behind Lasers

1. Understanding Energy Level Transitions

At the heart of every laser lies a dance of electrons between discrete energy levels within an atom, ion, or molecule. According to quantum theory, electrons can absorb or emit energy only in specific quantized amounts. When an atom absorbs a photon, it jumps to a higher energy level; when it releases energy, it drops to a lower one. The way in which that energy is released determines whether the emission is spontaneous or stimulated.

2. Spontaneous Emission – Nature’s Way

Spontaneous emission occurs naturally when an excited atom or molecule returns to a lower energy state by emitting a photon. This process is:

• Random in direction: The emitted photon can go in any direction.
• Random in phase: There is no phase relationship between photons.
• Incoherent and broad: The resulting radiation spreads over many wavelengths.

This is the principle behind ordinary light sources like incandescent bulbs and even stars. The emission is uncontrolled, and the resulting light lacks both coherence and directionality.

Fig 2. Spontaneous emission: Emission of light without external triggering.

3. Stimulated Emission – The Basis of Lasers

Stimulated emission was proposed by Albert Einstein in 1917 and is the fundamental mechanism that enables lasers. When an already excited atom is struck by a photon whose energy exactly matches the energy difference between two levels, it gets "triggered" to emit a second photon.

The resulting photon:

• Has the same frequency as the incoming photon
• Is in phase (temporal coherence)
• Moves in the same direction (spatial coherence)

This duplication of photons creates a domino effect inside the laser cavity, amplifying light exponentially. The more photons inside the cavity, the more stimulated emissions occur, making the laser beam stronger and more uniform.

Fig 3. Stimulated emission: The trigger for laser amplification.

4. Einstein Coefficients and Emission Rates

Einstein formalized these two processes using what are now called the Einstein Coefficients:

• A₂₁: Probability per unit time of spontaneous emission
• B₁₂: Probability per unit time of absorption
• B₂₁: Probability per unit time of stimulated emission

In lasers, we aim to maximize the effects of B₂₁ (stimulated emission) while suppressing spontaneous processes. This is why temperature control and cavity design are so important in laser engineering.

5. A Simple Analogy

Think of spontaneous emission like a person randomly throwing a single ping-pong ball into a room. Stimulated emission, on the other hand, is like clapping your hands in a hall and causing everyone else to clap in perfect rhythm and direction. This controlled cascade is what makes lasers so powerful and precise.

6. Comparison Summary: Spontaneous vs Stimulated

Feature	Spontaneous Emission	Stimulated Emission
Trigger	None (natural decay)	Incident photon
Phase Relation	Random	In phase
Directionality	Random	Same direction as trigger photon
Output Light	Incoherent	Coherent

Population Inversion – Creating the Right Conditions for Laser Action

1. What is Population Inversion?

In normal thermal conditions, atoms in a system are more likely to be in their ground state (lowest energy level) than in excited states. This statistical arrangement is governed by the Boltzmann distribution. However, for laser action to occur, we need an unusual and non-equilibrium condition where:

The number of atoms in the excited state exceeds those in the lower energy state.

This is known as Population Inversion, and it is the essential prerequisite for stimulated emission to dominate over absorption.

2. Why Is It Needed for Laser Operation?

Without population inversion, any incident photon is more likely to be absorbed than to stimulate emission. In such a state, the medium behaves like a light absorber, not an amplifier.

But once the excited state population overtakes the ground state, each incoming photon is more likely to stimulate an identical photon, resulting in coherent amplification of light — the signature of laser action.

3. Two-Level vs Three-Level and Four-Level Systems

Achieving population inversion in a two-level system is nearly impossible because the same transition is used for excitation and emission — any energy added immediately triggers absorption.

Therefore, practical lasers use either three-level or four-level systems:

• Three-Level System

In this setup:

1. Atoms are pumped from ground state (E₁) to a higher level (E₃).
2. They rapidly decay (non-radiatively) to a long-lived metastable level (E₂).
3. Stimulated emission occurs from E₂ to E₁.

Drawback: More than 50% of atoms must be excited to surpass the ground state population.

• Four-Level System

More efficient and commonly used:

1. Pumping moves atoms from ground state (E₀) to E₃.
2. Quick decay to metastable level E₂.
3. Stimulated emission occurs from E₂ to E₁.
4. Final decay to E₀.

Advantage: The lower laser level (E₁) has very few atoms, making population inversion easier to achieve.

Fig 4. Four-level system—widely used in Nd:YAG and CO2 lasers.

4. Methods of Achieving Population Inversion

Various techniques are used to excite atoms to higher energy levels, depending on the laser type:

• Optical Pumping: Intense light (usually from flashlamps or another laser) is used to raise electrons. Used in ruby and Nd:YAG lasers.
• Electrical Discharge: A high-voltage current excites gas atoms, common in He-Ne and CO₂ lasers.
• Chemical Reactions: Energy from chemical reactions drives transitions, as seen in chemical lasers used in defense.
• Semiconductor Injection: Electrons and holes are injected into a junction in diode lasers, triggering recombination and photon emission.

5. Real-Life Examples

- In a He-Ne laser, helium atoms are excited by electric discharge and then transfer energy to neon atoms, which achieve a metastable state — enabling population inversion.

- In a Nd:YAG laser, optical pumping by flashlamps excites neodymium ions to a metastable level, ready for stimulated emission at 1064 nm.

6. Conclusion

Population inversion is not just a requirement—it is the **backbone** of laser operation. Without it, the chain reaction of stimulated emission that defines laser behavior cannot begin. Creating and maintaining this inverted population through efficient pumping mechanisms and system designs is the art and science of laser physics.

Different Types of Pumping – Fueling the Laser Engine

1. What is Pumping in Lasers?

Pumping is the process of supplying energy to the laser medium to raise atoms or electrons from a lower energy state to a higher (excited) state. This is essential for creating population inversion, the critical condition for laser amplification. Without an efficient pumping mechanism, stimulated emission cannot outpace absorption, and laser action becomes impossible.

Different laser types use different pumping techniques, depending on their medium (gas, solid-state, liquid, or semiconductor) and application requirements.

2. Optical Pumping

Optical pumping uses intense light sources, such as flashlamps or arc lamps, to excite atoms in the gain medium. Photons from the pump source are absorbed by the active atoms, raising them to excited states.

Used in: Solid-state lasers like Ruby and Nd:YAG.

Advantages: Simple to implement and effective for narrowband energy transitions.

Drawbacks: Inefficient energy usage; a lot of light is lost as heat.

Fig 5. Flashlamp-based optical pumping in solid-state lasers.

3. Electrical Discharge Pumping

In this method, a high-voltage electric current passes through a gas medium, energizing atoms through collisions with free electrons. This raises them to higher energy levels.

Used in: Gas lasers such as He-Ne, Argon-ion, and CO₂ lasers.

Advantages: Efficient and cost-effective for continuous operation.

Drawbacks: Requires stable and controlled discharge systems to prevent overheating or instability.

Fig 6. Electrical excitation for gas lasers.

4. Semiconductor Injection (Electrical Injection)

Widely used in diode lasers, this method involves injecting electrons and holes across a p-n junction. Recombination at the junction produces photons, achieving population inversion within the semiconductor.

Used in: Semiconductor lasers like laser diodes in CD/DVD drives, barcode scanners, and fiber-optic communication.

Advantages: Compact, highly efficient, low power consumption, and fast switching speed.

Drawbacks: Limited power output and beam quality compared to bulkier systems.

5. Chemical Pumping

Chemical lasers derive their energy from exothermic chemical reactions. The energy released excites the molecules directly to a metastable state without external light or electrical input.

Used in: High-power military lasers like the Chemical Oxygen Iodine Laser (COIL).

Advantages: Extremely high power and energy scalability.

Drawbacks: Complex setup, toxic chemicals, not suitable for consumer or clinical applications.

6. Energy Transfer Pumping

In some systems, one species (e.g., helium atoms in He-Ne lasers) is excited and then transfers energy to another species (e.g., neon) through inelastic collisions. This indirect pumping is essential for certain multi-gas systems.

Used in: He-Ne laser and some dye lasers.

Advantages: Allows precise control over energy delivery and transitions.

Drawbacks: Requires precise control over gas ratios and conditions.

7. Comparative Summary

Type of Pumping	Medium	Example Laser	Key Advantage
Optical	Solid-state	Ruby, Nd:YAG	Simple implementation
Electrical Discharge	Gas	He-Ne, CO2	Low-cost and efficient
Semiconductor Injection	Semiconductor	Laser Diode	Compact and energy-efficient
Chemical	Gas (reactive)	COIL	High power output
Energy Transfer	Gas mixture	He-Ne	Precision excitation

8. Conclusion

The method of pumping directly influences the efficiency, design, cost, and application of a laser system. Whether through light, electricity, or chemical energy, the ultimate goal remains the same: achieve and sustain population inversion to produce coherent laser light. Understanding these mechanisms lays the foundation for choosing or designing the right laser for the task.

Characteristics of LASER – What Makes Lasers Unique

1. Introduction

Lasers differ dramatically from conventional light sources like incandescent bulbs or LEDs. What makes a laser beam so powerful, focused, and coherent lies in its unique physical characteristics. These attributes are not accidental—they result from careful manipulation of atomic processes and resonator design. In this section, we explore the defining features that make lasers indispensable in modern technology.

2. Coherence (Temporal and Spatial)

Coherence is the hallmark of laser light. It refers to the predictable phase relationship between photons.

• Temporal Coherence: All photons maintain the same phase over time. This allows the laser to interfere with itself even over long distances.
• Spatial Coherence: All light waves are in phase across the beam cross-section, enabling the formation of narrow, focused beams.

Result: Interference, holography, and high-precision measurement are possible due to high coherence.

3. Monochromaticity

A laser emits light of a single wavelength (or a very narrow band), unlike ordinary white light which spans a broad spectrum. This property arises from the discrete energy transitions in atoms.

Example: A typical He-Ne laser emits at 632.8 nm with a linewidth of just a few MHz.

Benefit: Monochromatic light is essential in spectroscopy, communication, and optical data storage.

4. Directionality

Laser beams are highly directional, meaning they propagate in a single, narrow path with very low divergence. This is due to the resonant optical cavity that amplifies only parallel rays.

Comparison: A laser beam may diverge at less than 1 milliradian, whereas light from a bulb spreads in all directions.

Advantage: Allows high-intensity delivery over long distances (e.g., in fiber optics and laser pointers).

5. High Intensity (Brightness)

Because of directionality and coherence, lasers can concentrate energy into very small areas, resulting in extremely high power densities.

Example: Industrial cutting lasers can deliver thousands of watts into a beam just millimeters wide.

Application: Enables medical surgeries, material processing, and scientific experimentation requiring high energy density.

6. Polarization

Lasers can emit light that is linearly or circularly polarized depending on the resonator design. This property allows precise interaction with materials and biological tissues.

Use Case: In optical trapping, polarization is used to manipulate particles at the micro and nano scale.

7. Comparison with Ordinary Light

Property	Ordinary Light	Laser Light
Coherence	Incoherent	Highly coherent
Monochromatic	Broad spectrum	Single wavelength
Directionality	Divergent	Highly directional
Intensity	Low	Very high
Polarization	Random	Controlled

8. Conclusion

The distinct properties of laser light—coherence, monochromaticity, directionality, intensity, and polarization—are what make it suitable for a wide range of precise and powerful applications. These characteristics are not just theoretical; they are harnessed in real-world fields like medicine, communications, defense, and engineering.

Types of Lasers – He-Ne, Nd:YAG, CO₂, and Semiconductor Lasers

1. Helium-Neon (He-Ne) Laser

The He-Ne laser is a gas laser, commonly used in laboratories, holography, barcode scanning, and educational demonstrations. It is one of the first types of continuous-wave (CW) lasers developed and still popular due to its simplicity and stable output.

Construction:

• Glass tube filled with helium and neon gases in the ratio 10:1
• Electrodes at both ends apply high voltage to excite helium atoms
• Two mirrors form the resonator: one fully reflective, one partially transparent

Working Principle:

An electrical discharge excites helium atoms, which then transfer energy to neon atoms through collisions. The neon atoms reach a metastable excited state. Population inversion is achieved, and stimulated emission at 632.8 nm (red light) occurs.

Key Features:

• Wavelength: 632.8 nm (visible red)
• Output power: 0.5 to 50 mW
• Highly stable and coherent

Applications:

Used in alignment systems, physics labs, barcode readers, interferometry, and holography.

2. Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) Laser

A solid-state laser, the Nd:YAG laser uses a synthetic crystal doped with neodymium ions (Nd³⁺). It is one of the most powerful and versatile lasers in industrial and medical applications.

Construction:

• Nd:YAG rod as the active medium
• Flashlamp or diode lasers used for optical pumping
• Highly reflective mirrors at each end forming the resonator

Working Principle:

Optical pumping excites neodymium ions to a metastable level. Stimulated emission occurs when the ions transition to a lower energy state, emitting infrared light.

Key Features:

• Wavelength: 1064 nm (infrared)
• Modes: Continuous or pulsed (Q-switched)
• High peak power and good beam quality

Applications:

Used in laser cutting, welding, dentistry, tattoo removal, eye surgeries (YAG capsulotomy), and military rangefinders.

3. CO₂ (Carbon Dioxide) Laser

The CO₂ laser is a gas laser known for its extremely high power output and efficiency. It is commonly used in industrial manufacturing and surgical procedures.

Construction:

• Gas mixture of CO₂, N₂, and He inside a long glass tube
• High voltage source to create electric discharge
• Mirrors at both ends form the optical cavity

Working Principle:

Electrical discharge excites nitrogen, which transfers energy to CO₂ molecules. CO₂ molecules then transition between vibrational energy levels, producing infrared radiation through stimulated emission.

Key Features:

• Wavelength: 10.6 µm (infrared)
• Output: Up to several kilowatts
• Very high efficiency: up to 20%

Applications:

Laser cutting of metal and plastics, engraving, medical surgeries, dermatology, and military uses like infrared weapon guidance.

4. Semiconductor Laser (Laser Diode)

Semiconductor lasers are compact, efficient, and used in almost every modern electronic device. They operate using electron-hole recombination in a p-n junction.

Construction:

• P-n junction made of semiconductor materials (e.g., GaAs)
• Current injected across the junction to provide energy
• Resonator formed by cleaved or coated end surfaces

Working Principle:

Electrons and holes recombine in the active region, releasing photons. If population inversion is achieved, stimulated emission occurs, and a coherent beam emerges.

Key Features:

• Wavelength: 630–1550 nm (varies by material)
• Very small size and low power consumption
• Modulatable: Can be turned on/off rapidly for communication

Applications:

Used in fiber-optic communication, laser printers, barcode readers, CD/DVD/Blu-ray drives, laser pointers, medical diagnostics, and sensors.

5. Summary Table: Comparing Four Laser Types

Laser Type	Medium	Wavelength	Pumping Method	Applications
He-Ne	Gas (He + Ne)	632.8 nm (red)	Electric discharge + energy transfer	Lab experiments, barcode scanning, alignment
Nd:YAG	Solid-state (crystal)	1064 nm (IR)	Optical pumping	Medical, industrial cutting, military
CO₂	Gas (CO₂ + N₂ + He)	10.6 µm (far IR)	Electric discharge	Metal cutting, surgery, engraving
Semiconductor	p-n junction	630–1550 nm	Electrical injection	Communication, consumer electronics

3-D Profiling Using Lasers – Precision Mapping and Imaging

1. What is 3-D Laser Profiling?

3-D laser profiling refers to the process of using laser beams to measure and reconstruct the three-dimensional shape or surface topology of an object. By analyzing how laser light reflects or scatters from an object, highly accurate digital models can be generated in real-time. This technology is widely used in industries such as manufacturing, medicine, robotics, and geospatial mapping.

2. How Does It Work?

There are several techniques through which lasers are used for 3-D profiling. The most common include:

• Laser Triangulation: A laser beam is projected onto a surface, and a camera captures the reflected spot from a known angle. The position of the spot helps calculate the distance using triangulation.
• Time-of-Flight (ToF): The time taken by a laser pulse to hit a surface and return is measured. Since light travels at a known speed, the distance is calculated precisely.
• Structured Light Scanning: A pattern of laser lines or grids is projected, and a camera captures distortions to determine surface contours.
• Interferometry: Laser interference patterns are analyzed to measure extremely fine surface variations down to nanometer precision.

Fig 7. Laser triangulation method for accurate 3D measurements.

3. Advantages of Laser-Based 3D Profiling

• Non-contact measurement: No physical touch means no wear and tear or surface damage.
• High speed and precision: Suitable for real-time quality control and high-volume inspections.
• Versatility: Works on metals, plastics, skin, terrain, and even fluids under specific conditions.
• Automation-friendly: Easily integrated into robotic arms, conveyor belts, or drones.

4. Key Applications

• Manufacturing: For detecting surface defects, dimensions, and alignment in real-time.
• Medicine: For facial reconstruction, orthotic fitting, and 3-D mapping of organs and skin.
• Architecture and Civil Engineering: Laser scanners generate 3D models of buildings, bridges, and landscapes.
• Autonomous Vehicles: LIDAR (Light Detection and Ranging) uses laser pulses to detect obstacles and terrain in 3D.
• Forensics and Archaeology: Documenting crime scenes or ancient structures in fine detail.

5. Real-Life Example: LIDAR in Action

LIDAR systems mounted on drones or vehicles emit thousands of laser pulses per second to map the environment in 3D. The data is used in:

• Self-driving cars to avoid obstacles
• Forestry to estimate tree canopy height
• Disaster zones to evaluate landslides or floods

Fig 8. LIDAR technology using laser pulses for 3D mapping.

6. Limitations

Although powerful, laser-based profiling does have some limitations:

• Reflective or transparent surfaces can distort measurements.
• Ambient light interference can reduce accuracy outdoors.
• High cost for precision-grade equipment.

7. Conclusion

3-D profiling using lasers has revolutionized measurement, inspection, and modeling across industries. With advancements in scanning speed, resolution, and compact design, laser-based profiling continues to pave the way for smarter automation, better diagnostics, and deeper environmental insights.

Applications of Lasers – In the Field of Medicine & Ophthalmology

1. Introduction

Lasers have revolutionized medical science by offering unparalleled precision, minimally invasive treatment options, and faster healing. Their ability to focus light into tight beams allows for cutting, cauterizing, reshaping, and even regenerating tissue without damaging surrounding areas. Among all medical applications, ophthalmology stands out as one of the most impactful fields where lasers have become standard tools for both diagnosis and treatment.

2. General Applications of Lasers in Medicine

Lasers are widely used across various branches of medicine. Depending on the wavelength and power, lasers can either ablate (cut), coagulate (seal), or stimulate tissue.

• Dermatology: Used to remove tattoos, wrinkles, birthmarks, scars, and unwanted hair with minimal scarring.
• Surgery: CO₂ and Nd:YAG lasers are used for bloodless cuts, especially in delicate surgeries involving the brain, liver, or intestines.
• Oncology: Lasers are employed for photodynamic therapy (PDT) to treat early-stage cancers by activating photosensitizing drugs.
• Dental Treatments: Diode lasers are used for gum reshaping, teeth whitening, and cavity preparation with less pain and faster recovery.
• Orthopedics: Used to treat chronic pain and accelerate healing of tissues via low-level laser therapy (LLLT).

3. Applications of Lasers in Ophthalmology

The eye is a delicate organ where micro-level precision is critical. Lasers provide the surgeon with unmatched accuracy in targeting minute structures inside the eye.

• LASIK (Laser-Assisted In Situ Keratomileusis)

LASIK uses an excimer laser to reshape the cornea, correcting refractive errors like myopia, hyperopia, and astigmatism. This outpatient procedure is quick, with most patients recovering vision within 24–48 hours.

• PRK (Photorefractive Keratectomy)

PRK is an alternative to LASIK for patients with thin corneas. The surface layer is removed and the cornea reshaped using an excimer laser. Healing time is slightly longer, but results are comparable.

• YAG Laser Capsulotomy

After cataract surgery, the lens capsule can become cloudy. A YAG laser is used to create a clear opening in the posterior capsule, restoring vision in seconds.

• Retinal Photocoagulation

Argon or diode lasers are used to seal leaking blood vessels in diabetic retinopathy and to treat retinal tears. The laser burns prevent further fluid leakage or retinal detachment.

• Glaucoma Treatment (Laser Trabeculoplasty)

Lasers help improve drainage in the eye’s trabecular meshwork, reducing intraocular pressure in glaucoma patients without incisions.

Fig 9. LASIK surgery: Using lasers to correct corneal shape and eliminate glasses.

4. Advantages of Using Lasers in Medical Applications

• Minimally invasive – smaller incisions, less bleeding
• High precision – targeted treatment with minimal tissue damage
• Reduced infection risk due to cauterization
• Shorter hospital stays and faster recovery times
• Greater comfort for the patient during and after procedures

5. Safety and Limitations

Although laser procedures are safe when used properly, there are potential risks:

• Eye damage if improper protective eyewear is used
• Scarring or burns from improper calibration or technique
• High cost of equipment and specialized training required

Regulatory standards such as ANSI Z136.1 and IEC 60825-1 ensure safe usage in clinical environments.

6. Conclusion

Lasers have become indispensable in modern medicine. From painless vision correction to scar-free surgeries and cancer treatment, they are reshaping how healthcare is delivered. In ophthalmology especially, lasers have brought about life-changing results, restoring sight and preventing blindness for millions. With continued advancements, lasers will play an even greater role in minimally invasive, high-precision medical care.

For more units of physical optics click below 👇 

👉 Unit 1 Nature of light (part 1)

👉 Unit 1 Source of light (part 2)

👉 Unit 2 Interference of Light 

👉 Unit 3 Diffraction and Scattering 

👉 Unit 4 Polarization of light