Lasers: Light Amplification

• Laser stands for Light Amplification by Stimulated Emission of Radiation
• A laser generates an intense beam of coherent monochromatic light
• This is achieved through stimulated emission of photons from excited atoms or molecules

Laser Types & Components

• A Helium-Neon gas in a glass tube or a semiconductor diode can be used as a laser source
• He-Ne or semiconductor diodes produce monochromatic and coherent light
• This light emitted's wavelength is determined in the experiment
• A He-Ne laser is a gas laser that uses a mixture of helium and neon gas as its laser source
• Gas lasers are more commonly used compared to semiconductor or solid-state lasers
• Electron excitation in the He-Ne gas medium is achieved by passing an electric current through the gas
• He-Ne lasers operate at a wavelength of 632.8 nm, which is in the red portion of the visible spectrum
• A helium-neon gas laser setup includes a DC power supply, cathode, anode, helium-neon gas mixture, output coupler, glass tube and high reflector

Determining Laser Wavelength with Diffraction Grating

• Diffraction describes waves spreading out as they pass through an aperture or around obstacles
• The experiment's aim is to determine a given laser's wavelength using a diffraction grating

Experiment Objectives

• Measure the distance between the diffracting grating and the screen
• Measure the distance between the laser source and diffracting grating
• Shine the laser through the grating
• Measure the distance between the central fringe and the first order fringe
• Calculate the wavelength of laser using a formula

Apparatus

• Essential equipment includes a laser source (He-Ne or semiconductor)
• A transmission grating is required
• An optical bench is needed to hold components
• Also needed is a screen to observe the diffraction pattern
• A meter scale is required for measuring distances

Procedure Outline

• Place the laser source on the optical bench to generate a horizontal beam
• Position the diffracting grating on its stand in front of the laser source, ensuring it is normal to the laser beam
• Place the screen a distance d from the grating
• Switch on the power source to produce a laser beam incident normally on the grating, then focus the light on the zero mark

Results & Analysis

• The laser beam diffracts at varying angles from the brightest spot on the screen
• The central, brightest spot represents the central maximum, or fringe
• Measure the distances x1, x2, etc., of the different spots from the central maximum on both sides
• Calculate the average distance x for each order

Calculations

• Find the tangent inverse of the ratio between x and d for the first order to determine the angle theta (Θ)
• Calculate the sine of Θ and use it in the formula λ = sinΘ/Nn
• N represents the number of lines per grating
• Ordinary grating material has N = 10^5 lines per meter
• "n" is the diffraction order (no unit)
• Θ is the angle of diffraction, measured in degrees
• λ represents the wavelength of the laser light, measured in angstroms (A°)
• One angstrom equals 10^-10 meters, or one nanometer

Laser Applications

• Laser light possesses unique properties such as coherency, monochromacy, directionality, and high intensity
• Lasers are different from ordinary light due to their various unique properties
• These properties allow lasers to be used in medicine, communications, industries, science, technology and military