What Is a Laser Diode?
A laser diode, unlike an ordinary LED, is a diode that produces focused, single-wavelength and coherent light. It's the source of laser light.
How Does It Differ From an LED?
An LED emits scattered light over a wide angle and at many wavelengths. A laser diode amplifies the light in an optical cavity to form a narrow, single-color beam in the same phase; this lets it be focused very far.
Threshold Current
Below a certain current (the threshold current) a laser diode only glows like a weak LED. Above the threshold the laser effect suddenly begins and the brightness rises rapidly. So the current control must be very precise.
| Property | LED | Laser Diode |
|---|---|---|
| Light | Scattered | Focused beam |
| Wavelength | Wide | Very narrow |
| Coherence | None | Yes |
The Need for Precise Driving
Laser diodes are very sensitive to overcurrent and electrostatic discharge (ESD); even a moment above the threshold can permanently damage the diode. So they're fed with special constant-current drivers.
Where Is It Used?
CD/DVD/Blu-ray readers, laser printers, fiber-optic communication, barcode readers, laser pointers and rangefinders.
Common Mistakes
- Giving current uncontrolled: even short pulses above the threshold can burn the diode.
- No ESD protection: static electricity easily damages a laser diode.
- Eye safety: looking at the laser beam with the naked eye is dangerous.
Frequently Asked Questions
Why is a laser diode more expensive?+
Is it the same as a laser pointer?+
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