Laser Diodes

Laser diodes are semiconductor devices that emit a concentrated power density of light. This is possible when an electric potential is applied across their P and N layers. A high-reflectivity dielectric coating is applied to the rear facet of the laser chip. This ensures that more of the light is emitted from the front facet. The front facet is also coated with a low-reflection coating (often 2 or 3% reflectivity, depending on the power), to further increase the efficiency and reflect only the minimum amount of light required for lasing. In addition, a region is etched on the active layer, which becomes the waveguide and confines the light in the lateral dimension. The light is confined to the vertical dimension of the waveguide by the top and bottom cladding layers.

Depending on the dimensions of the waveguide, its numerical aperture, wavelength, and other factors, the laser can be either single mode or multimode. A single mode laser diode emits a Gaussian beam. This single mode beam has the lowest divergence of any type of laser beam when it propagates in space, as well as the lowest etendue (French for the word "spread," as it describes the minimum divergence that can be achieved for a given collimated beam diameter. A multimode laser diode, also sometimes referred to as a broad area waveguide (BAL), has a larger waveguide. When a broad area laser is collimated, the light has far greater divergence; the BAL effectively behaves in some ways like an LED, due to the larger emitter.

However, divergence can be reduced for any laser by collimating it with a lens having a longer focal length. In fact, for a given collimated beam from any laser diode, its divergence is directly inversely proportional to the focal length of the lens used. Typically, a high-quality aspheric lens is chosen as the collimation lens because the laser's low-etendue characteristics, or low divergence, can be preserved. Aspheric lenses can also be quite cost-effective when produced by molding in volume. This combination makes a very cost-effective laser module.

Laser diodes are incorporated in into products for various applications. Too numerous to list comprehensively, uses include engraving, cutting and marking on a variety of materials such as metals, woods, and plastics. Diode lasers can also be used as a light source for sample illumination in the life sciences. For example, laser diodes are often incorporated into the light source for a fluorescence microscope. One of the main advantages of using laser diodes as the light source for medical and science applications, including microscopy, is that laser light tends to be spectrally dense. Usually, the semiconductor laser's emitted light spectrum is concentrated within a small region in wavelength space of 2nm or less. It can be further narrowed by adding a wavelength selection element, which can be either integrated longitudinally within the waveguide structure externally or be positioned externally. However, for engraving lasers, the spectral width is less critical as the center wavelength.

Violet and blue laser diodes at the 405nm, 445nm or 450nm wavelengths are ideal for laser heads used for engraving, marking, and cutting for a variety of reasons. The short wavelength light is strongly absorbed by many materials, have low-etendue characteristics resulting from a typically narrow waveguide structure for highly concentrated power densities, are high-power (up to and exceeding 6W at the time of writing), relatively impervious to temperature, and have a long lifetime. Opt Lasers integrates blue and violet laser diodes into their engraving laser heads for these and other reasons. More information about the advantages of using blue laser diodes.

In addition to integrating laser diodes into engraving lasers and scientific lasers, Opt Lasers also sells individual laser diodes, often in TO-can packages. Typical standards we provide include 3.8mm (TO-38), 5.6mm (TO-56) and 9mm (TO-18). Opt Lasers provides laser diodes at a variety of wavelengths, including 405nm, 445nm, 465nm, 473nm, 488nm, 505nm, 520nm, 638nm, 808nm, 830nm, 850nm, 980nm, and 1060nm, both free-space and fiber-coupled. Feel free to contact us if there is another wavelength that you need for your application.

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