Advanced Laser & Optics Learning LabYoung's Double-Slit Interference
Two coherent slits produce a fringe pattern on a screen. Adjust wavelength, slit separation and screen distance and watch the live fringe pattern and the diffraction envelope that modulates it.
📖 Full theory, formulas & procedure for this in the User Guide → 📝 Open Lab Record & Viva-Voce Booklet (PDF) →d (slit separation) squeezes fringes closer together; increasing
D (screen distance) spreads them apart. This is the same physics behind Fresnel's biprism and
Newton's rings in BAS101 Unit 1.Single-, Double- and N-Slit Diffraction
Switch between a single slit, a double slit and a full diffraction grating. Watch how increasing the number of slits N sharpens the principal maxima — the working principle of a spectrometer grating.
📖 Full theory, formulas & procedure for this in the User Guide → 📝 Open Lab Record & Viva-Voce Booklet (PDF) →Polarization & Malus's Law
Light passes through a fixed polarizer, then an analyzer whose angle you control. Watch the E-field orientation and the transmitted intensity follow Malus's law, I = I₀cos²θ.
📖 Full theory, formulas & procedure for this in the User Guide → 📝 Open Lab Record & Viva-Voce Booklet (PDF) →Dispersion by a Prism
A prism bends different wavelengths by different amounts because refractive index depends on wavelength (normal dispersion: n is higher for blue/violet than for red). Adjust the prism's dispersive power and watch white light spread into a spectrum.
📖 Full theory, formulas & procedure for this in the User Guide → 📝 Open Lab Record & Viva-Voce Booklet (PDF) →🪞 Michelson Interferometer
A beamsplitter divides a laser beam into two arms, each ending in a mirror. Moving mirror M₁ changes the path difference between the arms, and the recombined beams form a circular fringe pattern that expands or collapses at the centre as the mirror moves — the classic length-measurement instrument.
Focusing of Light by a Convex Lens
Parallel rays entering a convex lens converge to a focal point. Adjust focal length and aperture (lens diameter) and see both the ray-traced focus and the diffraction-limited minimum spot size a real lens can achieve — geometry alone is never the full story once diffraction is included.
📖 Full theory, formulas & procedure for this in the User Guide → 📝 Open Lab Record & Viva-Voce Booklet (PDF) →Image Formation by a Compound Lens System
Trace rays through two thin lenses in series (as in a microscope or telescope eyepiece pair). Move the object and change each lens's focal length and their separation, and watch the intermediate image from lens 1 become the object for lens 2. Drag the diagram left/right to pan, and use the zoom control if the image falls outside the view.
📖 Full theory, formulas & procedure for this in the User Guide → 📝 Open Lab Record & Viva-Voce Booklet (PDF) →The Photoelectric Effect
Shine light of a chosen frequency and intensity onto a metal plate. Below the threshold frequency, no electrons are ejected — however bright the light. Above threshold, electrons are ejected instantly, with a maximum kinetic energy that depends only on frequency, not intensity.
Compton Scattering
An X-ray photon collides with a free electron like a billiard-ball collision, transferring some momentum and losing energy — its wavelength increases. Change the scattering angle and see the wavelength shift predicted by the Compton formula, direct evidence that photons carry momentum p = h/λ.
Single-Photon Double-Slit Build-up
Photons are sent through a double slit one at a time. Each one lands as a single, random-looking dot — yet after thousands of individual "particle" arrivals, an interference pattern emerges. This is perhaps the single most direct demonstration of wave–particle duality.
Coherence Length & Coherence Time
Real sources never emit a perfectly single frequency — they have some spectral linewidth Δν. This limits how far apart two points on the wave can be and still interfere with a well-defined phase relationship: the coherence time τc ≈ 1/Δν and coherence length Lc = cτc. Widen the linewidth and watch the interference fringes lose contrast (visibility) at larger path differences.
📖 Full theory, formulas & procedure for this in the User Guide → 📝 Open Lab Record & Viva-Voce Booklet (PDF) →Directionality & Beam Quality
A laser's optical cavity forces emission into a narrow set of directions (a low-divergence beam) — very different from an ordinary lamp, which radiates in all directions. Compare beam spread over distance for a laser vs. a conventional source.
📖 Full theory, formulas & procedure for this in the User Guide → 📝 Open Lab Record & Viva-Voce Booklet (PDF) →Monochromaticity & Spectral Purity
Monochromaticity describes how close a source comes to emitting a single wavelength. Compare the emission spectrum of a laser (extremely narrow line) against an LED and a white-light source (broad continuum).
Making a Hologram
A hologram records the interference between light scattered off an object and a coherent reference beam, capturing both amplitude and phase. Step through the recording and reconstruction stages below.
Red → Ultraviolet: What Changes as Frequency Increases?
Slide from deep red (near-infrared boundary) through the visible spectrum into the ultraviolet, and see how colour, photon energy, and physical hazard all change together — higher frequency light carries more energetic (and more dangerous) photons.
📖 Full theory, formulas & procedure for this in the User Guide → 📝 Open Lab Record & Viva-Voce Booklet (PDF) →Laser Safety, Precautions & Potential Harm
Every experiment in BAS101, MPY301, BAS151 and MPY351 that involves a real laser (Newton's rings/biprism with laser sources, He-Ne alignment, Ruby/Nd:YAG demonstrations, laser diffraction) carries real hazards. This section is not optional reading — review it before touching any laser apparatus in the lab.
📖 Full theory, formulas & procedure for this in the User Guide →Laser Hazard Classes (IEC 60825-1)
| Class | Typical power | Hazard level | Examples |
|---|---|---|---|
| Class 1 | < 0.4 mW (visible, CW) | Safe under normal use; no known biological hazard | Laser printers, CD/DVD/Blu-ray players (enclosed) |
| Class 1M | Varies | Safe unless viewed with magnifying optics (binoculars, telescopes) | Fibre-communication test sources |
| Class 2 | < 1 mW (visible) | Blink reflex (~0.25 s) normally protects the eye — do not stare deliberately | Basic laser pointers, barcode scanners |
| Class 3R | 1–5 mW | Low risk but direct beam viewing should be avoided | Some laser pointers, alignment lasers |
| Class 3B | 5–500 mW | Hazardous to the eye from direct beam and specular reflections; diffuse reflection usually safe | Typical teaching He-Ne and diode lasers used in BAS101/MPY301/BAS151/MPY351 experiments |
| Class 4 | > 500 mW | Hazardous to eye and skin from direct, specular AND diffuse reflections; fire and ignition risk | Nd:YAG/Ruby/CO₂ industrial and research lasers (MPY301 Unit 5 processing lasers) |
👁️ Eye Injury
The eye focuses laser light onto the retina exactly as it focuses any other light — but a coherent, collimated beam concentrates enormous power density onto a tiny retinal spot. Possible outcomes include permanent blind spots (retinal burns/scotomas), retinal haemorrhage, and — for UV/IR lasers — corneal or lens damage, since these wavelengths are absorbed before reaching the retina at all. Damage from a visible Class 3B/4 beam can occur in a fraction of a second, faster than the natural blink reflex.
🔥 Skin & Tissue Burns
Class 4 beams (and even some Class 3B beams focused to a point) can burn skin, ignite clothing, paper, or solvent vapours, and damage optical components not rated for the beam's power. Reflected beams from jewellery, watches or metallic tools are a commonly overlooked hazard.
⚡ Electrical Hazards
Gas lasers (He-Ne, Ar-ion) and flashlamp-pumped solid-state lasers (Ruby) use high-voltage power supplies (kilovolts) to strike the discharge or fire the flashlamp. Capacitor banks in pulsed systems can retain a lethal charge even after the supply is switched off.
🧪 Chemical / Fume Hazards
Dye lasers use organic dyes dissolved in solvents that may be toxic, flammable or carcinogenic; some excimer lasers use toxic or corrosive gases (e.g. fluorine-based mixtures) that require proper gas handling and ventilation.
✅ Mandatory Precautions Before & During a Laser Experiment
- Wear correctly rated laser safety goggles — matched to the laser's wavelength and power, not generic sunglasses or safety glasses. Verify the optical density (OD) rating covers your specific laser.
- Never place your eye at beam height. Keep the beam path at chest level or below whenever possible, and always know exactly where the beam and its reflections are travelling.
- Remove reflective objects — wristwatches, rings, metallic pens, ID cards — from the beam path before aligning any optics.
- Enclose or terminate the beam path with a non-reflective beam block/dump at the end of its travel so it cannot escape into occupied space.
- Work in a well-lit room when practical — dark rooms encourage the pupil to dilate, increasing the amount of light entering the eye if an accidental exposure occurs. (Some alignment tasks genuinely require dim light — in that case, keep exposure time and direct viewing to an absolute minimum and rely on beam viewing cards, not the naked eye.)
- Never look into the beam to "check if it's on". Use a beam card, IR viewer, or power meter instead — never your eye, and never a co-worker's eye.
- Align at reduced power first wherever the laser/power supply allows, then increase to working power only once the beam path is fully controlled and enclosed.
- Post a warning sign ("LASER IN USE — DO NOT ENTER") and, for Class 3B/4 systems, use an interlocked door or curtain so nobody can walk into the beam path unexpectedly.
- Know your laser's class and maximum permissible exposure (MPE) before starting; this information is on the manufacturer's label and safety datasheet.
- Never defeat safety interlocks on laser housings, and never attempt to service the internal high-voltage power supply or flashlamp circuitry without qualified supervision — stored charge can be lethal even with the unit "off".
- Keep flammable solvents, papers, and gas cylinders away from the direct beam path of any Class 4 laser used for materials-processing demonstrations.
- Report every incident — even a suspected brief exposure — to the lab in-charge immediately; retinal injury is not always immediately painful or obvious.
🚫 Common Mistakes That Lead to Injury
- Looking along the beam axis "to see if it's aligned" instead of using a card or viewer.
- Assuming a "low-power" laser pointer or diode module is harmless — many exceed Class 2 limits and can still injure the retina with sustained or repeated exposure.
- Leaning over the optical table so the eye is at beam height while adjusting mirrors or lenses.
- Wearing sunglasses instead of laser-rated goggles — sunglasses provide essentially zero protection against the specific, narrow-band wavelength a laser emits.
- Not accounting for specular reflections from lens mounts, mirror edges, or metal tools left on the table.
- Running a Class 3B/4 beam through an open door or window into a corridor or another room.
🕳️ Laser Drilling
Operate a pulsed Nd:YAG drilling station and produce a precision hole to specification.
📖 Full theory, formulas & procedure for this in the User Guide →Drill a precision blind hole in a 2 mm stainless-steel sheet using a pulsed Nd:YAG laser. Aim for a clean, round hole with minimal heat-affected zone (HAZ) — too little energy leaves the hole incomplete; too much energy or too many pulses widens the HAZ and distorts the hole.
✂️ Laser Cutting
Operate a CO₂ laser cutting station with oxygen assist gas to produce a clean, dross-free cut.
📖 Full theory, formulas & procedure for this in the User Guide →Cut a 5 mm mild-steel plate with a CO₂ laser using oxygen assist gas. Aim for a narrow, smooth kerf with no dross (re-solidified molten metal) adhering to the bottom edge.
🔗 Laser Welding
Join two aluminium sheets with a fibre laser, achieving full penetration with no porosity.
📖 Full theory, formulas & procedure for this in the User Guide →Weld two 2 mm aluminium sheets edge-to-edge using a fibre laser. Aim for full-depth penetration with a smooth bead and no gas-porosity voids trapped in the weld.
🧪 Laser Surface Alloying
Melt a Cr-Ni powder layer into a steel substrate to create a corrosion-resistant surface alloy.
📖 Full theory, formulas & procedure for this in the User Guide →Alloy a thin Cr-Ni powder layer onto a mild-steel substrate, producing a uniform, well-mixed surface layer roughly 0.5 mm deep — patchy melting leaves an uneven, poorly bonded surface.
🧵 Laser Chemical Vapour Deposition (LCVD)
Deposit a uniform tungsten thin film by decomposing a precursor gas with a focused laser beam.
📖 Full theory, formulas & procedure for this in the User Guide →Decompose WF₆ precursor gas with a focused laser to deposit a ~200 nm tungsten film on a substrate. Aim for a uniform thickness across the scanned area — too little power/gas starves growth, too much causes uneven, over-thick deposits.
⚙️ Laser Hardening & Annealing
Surface-harden a steel gear tooth to a target case depth without melting the surface.
📖 Full theory, formulas & procedure for this in the User Guide →Harden the surface of a steel gear tooth to a case depth of about 0.8 mm using rapid self-quenching laser heating. Stay above the austenitizing temperature but below the melting point — melting ruins the surface finish, and insufficient heating leaves the case too shallow.
📡 LIDAR Ranging
Measure the distance to an unknown target using laser time-of-flight — read the echo, set your detection threshold, and estimate the range.
📖 Full theory, formulas & procedure for this in the User Guide →A pulse is fired at an unknown target and its echo is captured on the oscilloscope trace below. Move the measurement cursor onto the centre of the returned echo and set a sensible detection threshold above the noise floor, then read off the corresponding distance.
Laser Doppler Vibrometry
A laser beam reflected from a vibrating surface is Doppler-shifted in frequency by an amount proportional to the surface's instantaneous velocity. Mixing the reflected beam with a reference beam (heterodyne detection) recovers that velocity without ever touching the surface.
Optical Fiber — Numerical Aperture & Attenuation
Light launched into an optical fiber's core is trapped by total internal reflection only if it enters within a cone defined by the fiber's Numerical Aperture (NA). Meanwhile, the signal power decays exponentially with distance travelled, characterized by the fiber's attenuation coefficient.
Laser Speckle Metrology — Non-Contact Surface Roughness
When coherent laser light scatters off a surface whose height variations are comparable to or larger than the wavelength, the scattered wavelets interfere randomly and produce a grainy "speckle" pattern. The statistics of that pattern — its grain size and contrast — encode the surface's roughness.
