What are the most commonly used materials for Laser Diodes ?

Most commonly used materials for semiconductor lasers are the III-V compounds. These are such as GaAs, AlGaAs, InGaAs and InGaAsP depending upon the desired lasing wavelength emission.
Recently, GaN/AlGaN and InGaN/AlGaN are  being used to achieve laser diode emission in the green blue and ultraviolet regions.
InGaN (indium-gallium-nitride) is used for direct green laser diode emission.
Blue Diode Lasers (blue semiconductor laser diodes) are typically fabricated out of aluminum gallium nitride (AlGaN) or aluminum indium gallium nitride (AlInGaN).
Violet 405nm laser diodes and 375 nm UV laser diodes are based on either gallium nitride or indium gallium nitride.

What are the Typical Laser Diode Parameters ?

Threshold Current
:  The lowest current at which lasing action takes place.

Operating Current : Ideal laser diode operating current

Operating Voltage : The voltage across the laser diode at the specified operating current.

Wavelength : The output wavelength can vary from sample-to-sample and due to temperature.

Radiation Angle : The beam divergence parallel (horizontal) and perpendicular (vertical) relative to the gain region of the laser diode.

Positional and Angular Accuracy : The tolerance in mounting of the laser diode chip.

Differential Efficiency : Once the current threshold has been exceeded, the incremental increase in output power with current is fairly linear, measured in mW/mA. However, it can vary widely from sample-to-sample and with changes in temperature.

Astigmatism : The difference in virtual point source of the parallel and perpendicular beams.

Laser Diode Monitor Current : Sensitivity of the monitor photodiode with respect to laser diode output power.

What are some notable ranges of the electromagnetic spectrum?

The most familiar range is the visible spectrum – ranging from the short violet wavelengths to the the long red wavelengths. Most humans can see between 400nm and 700nm. Beyond the range of our vision exist shorter wavelengths of ultraviolet light, and longer wavelengths of infrared light. The higher the frequency of a photon, the more energy it has. World Star Tech carries laser diodes ranging from the ultraviolet 375nm to the infrared 1064nm.

How do you rate output laser power?

The output power of a laser is the maximum power of the light exiting the the laser housing. All World Star Tech lasers have their output power rated after passing through any installed optical assemblies. The power is measured according to CDRH specifications.

Each laser is classified by measuring the amount of optical power that would enter a 7mm aperture located at a distance of 20cm from the laser source. Our line lasers have a lower classification rating because the laser power is spread along the length of the line, rather than focusing on a single small point.

What determines the lifetime of a laser module?

Typical lifetime of laser diode modules are 25,000 to 50,000 hours. If the laser diode temperature rises beyond the maximum operating temperature the long-term performance may degrade significantly, up to and including complete failure. If the laser diode’s operating temperature is reduced by about 10 degrees, the lifetime will statistically double.

Laser module lifetime can be extended significantly by maintaining the case temperature at the low end of the operating temperature range. Heat sinks are recommended and must be used if the laser is operating constantly. Operating the laser modules at the low end of the recommended voltage range will also help to extend the lifetime of the laser.

What is bore-sight accuracy and beam pointing stability?

Boresight accuracy known as pointing accuracy, it is a measure of the angular difference between the beam propagating axis (where the laser beam is pointing) and the mechanical axis (where the laser housing is pointing). Pointing stability is a measure of how much the beam alignment drifts over a period of time.

The direction of the output beam of a laser is subject to some beam pointing fluctuations, which can in some cases cause significant problems – e.g., when the beam must be coupled into a single-mode fiber, or when the beam must precisely hit a target at a large distance. For such reasons, a quantitative measure for the beam pointing stability can be of importance.

In a weapon boresighting system for aircraft and vehicles, an optical square is oriented to a fixed reference line on the vehicle and provides the directionality of a pair of orthogonally positioned of laser illuminated retroreflective catadioptric collimators attached to said optical square whose outputs are directed via one or more deviators or periscopes to a pair of retroreflective catadioptric receivers orthogonally attached to a second optical square positioned at the weapon to be boresighted, each said receiver imaging the laser on a position sensitive sensor, the outputs of the latter indicating the pitch roll and yaw condition at the weapon.

What is laser beam divergence ?

Beam divergence specifies how much a beam spreads out over distance. All our beam divergence specifications are full angle values. The beam divergence of an electromagnetic beam is an angular measure of the increase in beam diameter or radius with distance from the optical aperture or antenna aperture from which the electromagnetic beam emerges. The term is relevant only in the “far field”, away from any focus of the beam. Practically speaking, however, the far field can commence physically close to the radiating aperture, depending on aperture diameter and the operating wavelength.

Beam divergence is often used to characterize electromagnetic beams in the optical regime, for cases in which the aperture from which the beam emerges is very large with respect to the wavelength. That said, it is also used in the Radio Frequency (RF) regime for cases in which the antenna is operating in the so-called optical region and is likewise very large relative to a wavelength.

Beam divergence usually refers to a beam of circular cross section, but not necessarily so. A beam may, for example, have an elliptical cross section, in which case the orientation of the beam divergence must be specified, for example with respect to the major or minor axis of the elliptical cross section.

What are some advantages of laser diode technology?

The commercial and industrial use of laser diodes has dramatically increased recently. The optical characteristics, small size, and ruggedness of laser diodes have allowed many new uses to be commercialized.

The output of laser diodes is very bright considering their small size. Today, hundreds of watts of power are commercially available from laser diodes operating under continuous wave (CW) conditions in packages as small as a few cubic inches. This characteristic makes these devices suitable for cable TV transmission, high definition TV (HDTV) development, and medical applications.

In addition, compared to other types of lasers, laser diodes use very little power. Most laser diodes operate with voltage drops of less than 2 V with power requirements determined by their current setting. Overall efficiencies greater than 30% are typical in the case of laser diodes. Since laser diodes are made of semiconductor materials, they do not require the fragile glass enclosures or mirror alignment typical of gas lasers. The resulting ruggedness and small size allow laser diodes to be used in environments and spaces in which other types of lasers cannot operate.

Coherence and single wavelength characteristics of laser diodes enable the outputs of these devices to be focused to a diffraction limited spot size. The size of the resultant spot is dependent on the wavelength of the laser – the shorter the wavelength of light, the smaller the size of the spot that can be generated. Operation at shorter blue and UV wavelengths makes smaller spot sizes possible, consequently allowing more information to be stored on optical disks at a higher density.

Another advantage of laser diodes is that they can be directly modulated at high frequencies. By modulating the drive current, the output of the laser diode is modulated with frequencies up to several GHz in high-speed data communications.