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12 Do’s and Don’ts for Laser Diodes
1. Laser Classification – You should know the classification of your laser and take the necessary precautions to avoid direct or indirect laser light. Moderate and high-power lasers are potentially hazardous because they can burn the retina of the eye or even the skin. To control the risk of injury, various specifications, for example, 21 Code of Federal Regulations (CFR) Part 1040 in the US and IEC 60825.
2. Eye Safety – Working with lasers can be dangerous, especially to the naked eye. Laser goggles, protective enclosures, etc. should be used in addition to safety equipment such as “laser active” signs, door interlocks, and switches. Ideally, diode lasers should be operated in a light-tight box, the door of which should be equipped with a switch, that shuts down the diode laser when the door is opened.
3. Electrostatic Discharge (ESD) – Most all laser diodes are very sensitive to damage by electrostatic discharge (ESD), or other voltage transients. ESD procedures are required when handling laser diodes. During shipment, the laser diode will be in a conductive plastic bag, and when possible, the anode and cathode electrical contacts shorted together to prevent ESD damage. When the laser is not connected to a power supply, the user should also short the anode and cathode electrical contacts. All persons and tools that may contact the laser must be continuously grounded.
4. Unpacking – Before opening the conductive plastic bag, diode lasers should be kept for at least 4 hours in the room where the bag will be opened to achieve thermal equilibrium. The protective bag should only be opened in a clean environment. The handling personnel and the tools used for handling must be grounded for ESDprotection purposes. During handling the personnel should wear clean gloves and use plastic tweezers to avoid contaminating the facets of the laser. Some lasers may be secured to a transport plate by fixing screws. Understand which screws are fixing screws and which screws are part of the assembly. Do not loosen the assembly screws which keep the diode laser together. The fixing screws may also be the shortcircuit between the anode and cathode electrical contacts to prevent ESD damage. The laser diodes must be kept in a clean and dry atmosphere with a temperature range of 0°C to 60°C once removed from the shipping containers.
5. Cleaning – Solvents, plastics, glues and heat conductive paste are not allowed near the laser diodes. These substances can outgas and deposit on optical surfaces including the laser diode facets. The laser diode front facet is extremely sensitive and must be kept free of dust, water, and any other kind of contamination. Any contact to the laser front facet will lead to irreversible damage and failure of the laser diode, even if there is no sudden failure. There is no way to clean the front facets by neither solvents nor by mechanical tools. The semiconductor crystal and its coatings are very sensitive to any kind of solvents and liquids. Do not touch the laser front facet with any object!
6. Laser Diode Driver – Laser diodes need to be operated with an approved laser diode driver that is current regulated and specifically designed for laser diodes. Off-the-shelf power supplies can deliver a high spike of current at turn-on, and/or deliver a very short duration reverse biasing when the unit is turned off. Either of these will damage or destroy the diode laser. Laser diodes are very sensitive to current and voltage spikes. Under all circumstances, spiking must be ruled out both for switching on and off and during the operation of the diode laser. The residual ripple of the current must not exceed a value of ± 10 %. The diode driver should also include a safety circuit that, in the case of faults, allows the system to be switched off within approx. 100 ms. Faults are all conditions which put the safety of persons or the device at risk.
7. Electrical Connections – Most laser diode drivers have provision to disable the supply and short the output to allow for connection of the diode. Never make the connection to the laser diode with the power supply voltage on.
8. Thermally-conductive Compounds – Pastes are typically not recommended for lasers. The liquids contained in these pastes liberate gas over time and can deposit on optical surfaces. Also, over time the initially homogeneous distribution of the paste can change to a mixture of conductive and non-conductive areas. This will impair the heat transfer from the laser.
9. Back Reflections – Some laser diodes are susceptible to damage from back reflections into the device. This is more common with lower wavelength material than with higher wavelengths. Thus, if attempting to collimate the output, or if there are optical components in the optical path, care must be taken to avoid back reflections. This can be more of an issue with fiber coupled or FAC lensed lasers because the optics help focus the back-reflected light into the laser.
10. Flammability – All objects exposed to laser radiation are subject to heating by the absorption of radiation power. Preclude exposure of flammable and/or combustible material to the radiation.
11. Noxious Substances – By the interaction of laser radiation with exposed materials, substances may be generated in the form of aerosols, gases and/or dust, which are injurious to health. Therefore, an appropriate exhaust device should be installed, and care needs to be taken to adequately clean the exhaust air for the specific application.
12. Laser Lifetime – By general, the end of life of a high-power diode laser is reached at the point in time at which the output power at constant current shows a reduction of 20%. To counter the effect of power loss, the operation current can be increased by up to 20% to maintain the nominal optical output power.
This laser diode lifetime rule is defined differently on some types of laser diodes.
You can read our full white paper on How to Improve Laser Diode Lifetime: Advice and Precautions on Mounting by clicking here.