laser pointers (original) (raw)

Definition: devices used for pointing at items with laser beams

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Contents

What are Laser Pointers?

A laser pointer is a small (usually battery-powered) laser device designed for pointing at objects by illuminating them with a collimated visible laser beam. Most laser pointers, particularly the cheap ones, contain a small GaInP/AlGaInP laser diode operating somewhere in the red spectral region, a collimating lens, a simple electronic diode driver, and a battery compartment for e.g. three coin cells.

Some laser pointers, as shown in Figure 1, emit green or even blue or yellow light. Some of them are based e.g. on directly green- or blue-emitting laser diodes. Others, which are significantly more expensive, contain a small diode-pumped solid-state laser with a nonlinear crystal for frequency doubling. Green laser pointers are often based on a miniature Nd:YVO4 laser with a KTP crystal for intracavity frequency doubling. Here, Nd:YVO4 is beneficial for a low threshold pump power, and KTP works in a relatively wide temperature range, thus not requiring means for temperature stabilization.

laser pointer

Figure 1: A green-emitting laser pointer, containing a tiny diode-pumped frequency-doubled solid-state laser. Red laser pointers are available in smaller sizes because they do not need as large batteries.

Laser pointers should not be confused with lamps containing light-emitting diodes (LEDs), which emit a much more diffuse beam (with much lower spatial coherence, similar to that of an incandescent lamp) and can also emit light with different colors, or white light. In contrast, laser points usually emit quasi-monochromatic light.

Applications

A typical use of a hand-held laser pointer is to point at some screen or chart during a presentation, e.g. a conference talk, to direct the viewer's attention to certain points. This is convenient because it can be done from a large distance and requires only a small hand-held device. However, the visibility of the generated spot on the screen is often poor (particularly for red laser pointers with relatively long emission wavelength), and a fast-moving light spot can have a somewhat nervous appearance. Therefore, some people prefer an old-fashioned telescopic pointing device for presentations.

Laser pointers can be useful for, e.g., aligning some machinery, or for certain optical distance measurements.

Brightness and Color

The apparent brightness of the illuminated spot depends strongly on the wavelength of the emitted light. Most devices operate in the red spectral region, where the sensitivity of the eye rapidly decreases with increasing wavelength. Devices with 650-nm output appear about twice as bright as those emitting the same power at 670 nm, and 635-nm devices still about two times brighter. However, the shorter-wavelength laser pointers are typically more expensive. This is particularly true for green lasers, which are significantly brighter than their red counterparts, but are still expensive. They involve a diode-pumped solid-state laser and a frequency doubler. Due to the typically poor conversion efficiency of the frequency doubler at low power levels, hundreds of milliwatts of infrared (typically 1064-nm) light are required for generating a few milliwatts in the green, and the batteries will accordingly not last very long, unless they are comparatively heavy.

Range of a Laser Pointer

Lay persons often ask what is the range of a laser pointer, and responding to this interest some producers specify some questionable numbers.

If the question is meant to be how far the light of a laser pointer can propagate, the correct answer is that there is no limit, provided that the light is not absorbed or scattered away in the atmosphere. However, the beam area will eventually become larger due to the beam divergence, so that the intensity e.g. on a screen will be reduced even if the overall power remains constant. Accordingly, an airplane pilot looking down into such a beam from an altitude of 10 km will not be disturbed by the remaining small intensity. (Exposure on a smaller distance could be quite problematic.)

The range of a laser pointer may also be understood as the maximum distance from which the spot on the screen can be seen. That kind of range is normally not limited by the beam divergence but by the overall optical power (apart from the wavelength and level of ambient light), since the issue is not the comparatively minor divergence on the way from the laser pointer to the screen, but rather the huge divergence of the scattered light on the way back. Therefore, someone standing next to the illuminated screen would easily see the spot when it is already hardly perceivable from the position of the laser pointer.

Safety Hazards

There have been extensive debates on laser safety issues associated with laser pointers. Typical output powers are a few milliwatts — normally below 5 mW to comply with safety class 3R, and sometimes below 1 mW for class 2. Direct staring into a 1 mW beam can be irritating for the eye: It can cause temporary flash blindness. However, one would normally not do that long enough to cause serious eye damage. Nevertheless, great care should be taken, e.g. when children are playing with laser pointers, if laser pointers are at all considered to be suitable as toys. Significant hazards could arise, for instance, if somebody walking down stairs or a car driver is distracted or dazzled by a laser beam.

There are some reports saying that cheap green laser pointers are sold which do not have a filter to eliminate the infrared light, and therefore can emit hundreds of milliwatts in the infrared spectral region. This is obviously a serious safety hazard; an eye directly hit by such a beam could be permanently damaged within a fraction of a second.

Because of such risks, most countries regulate the sale and use of laser pointers. Consumer devices are typically restricted to power levels of 1 mW or 5 mW, depending on national classification systems, to ensure that they remain within the safe range for momentary exposure. Higher-powered lasers are usually treated as industrial or research equipment, subject to licensing or professional-use requirements.

Laws also commonly prohibit aiming laser pointers at people, vehicles, or aircraft, since momentary blindness or distraction can cause accidents. In several jurisdictions, misuse of a laser pointer — particularly when directed at aircraft or law enforcement officers — is treated as a criminal offense, punishable by fines or imprisonment.

These regulatory measures reflect the view that laser pointers, while useful for presentations and educational demonstrations, are not toys and must be handled responsibly to prevent eye injuries and public safety incidents.

Use for Alignment

In principle, laser pointers can be used for alignment purposes. However, there are special alignment lasers which may be better suited for such applications. For example, they have a housing which can be more conveniently mounted, and the beam direction may be more stable.

Frequently Asked Questions

What is a laser pointer?

A laser pointer is a small, usually battery-powered laser device designed for pointing at objects by illuminating them with a visible, collimated laser beam.

How do laser pointers produce different colors like red and green?

Why does a green laser pointer appear much brighter than a red one of the same power?

The apparent brightness depends on the sensitivity of the human eye, which is much higher in the green spectral region than in the red. Therefore, a green spot appears significantly brighter than a red one with the same optical power.

What is the effective range of a laser pointer?

The beam itself can travel indefinitely unless absorbed or scattered. However, the visible range for pointing is limited by the optical power. The spot becomes hard to see from a distance because the scattered light returning to the viewer becomes too faint.

Are laser pointers dangerous?

Yes, they can be hazardous. While low-power pointers (class 2, <1 mW) are relatively safe, more powerful ones (class 3R, <5 mW) can cause eye irritation or temporary flash blindness. They pose a significant risk if misused, for example, by distracting drivers.

What is a specific danger associated with cheap green laser pointers?

Some cheap green laser pointers lack a filter to block the infrared pump light. They can dangerously emit hundreds of milliwatts of invisible infrared radiation, which could destroy an eye almost instantly upon direct exposure.

Are laser pointers subject to safety regulations?

Yes, there are various country-specific regulations, both concerning what laser pointers can be freely sold and how or where they may be used. Some dangerous abuses are heavily fined.

How does a laser pointer differ from an LED pointer?

A laser pointer emits a collimated, quasi-monochromatic beam with high spatial coherence. In contrast, a light-emitting diode (LED) emits a much more diffuse beam over a broader range of wavelengths.

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