In 1917, Einstein laid the groundwork for the LASER — Light Amplification by Stimulated Emission of Radiation. He conceived of stimulated emission: a photon interacts with an excited molecule or atom and causes the emission of a second photon having the same frequency, phase, polarization, and direction. This was the beginning of a whole new world of applications based on directed light.

miracleoniceeruzionegoalcelebration_crop_340x234In 1954, the development of the MASER — Microwave Amplification by Stimulated Emission of Radiation — at Columbia University served as a pre-launch of the technology. But it was Theodore Maiman, at Hughes Research Lab, who developed the first working laser in 1960.

One of the first applications of laser diodes was at the Winter Olympics in Lake Placid in 1980. Bell Labs created an experimental optical fiber system that was used to broadcast events to televisions around the world, including the U.S. vs Russia men’s hockey game. Today, more than 55,000 patents involving the laser have been granted. In 2010, the world celebrated the 50th anniversary of the laser.

Laser Diodes

Many of today’s laser systems are based on laser diodes, aka semiconductor lasers. Initially developed for fiber optic communications in the 1970s, the optical characteristics, small size, and ruggedness of diode lasers have encouraged a plethora of new uses, from spectroscopy to dermatology to industrial material processing. Thanks to the Internet and wireless communications, the hottest growth areas are optical fiber and data storage.

Laser_Diode_FabricationHundreds of watts of power are commercially available in packages as small as a few cubic inches. Laser diodes are quite bright but use very little power. Most operate with voltage drops of less than 2V with power requirements determined by their current setting. Overall efficiencies can reach 60% or more.

Microchannel Coolers

Laser manufacturers have made significant improvements to the amount of output power that can be produced by high-efficiency laser diode bars. Optical output powers have been demonstrated that are greater than 200W continuous wave (CW) from a single diode bar. These high powers test the limits of epitaxial structure design and dielectric coating design.

High performance laser diode bars require special packaging to manage heat. The most efficient method of cooling been gold-plated copper heat exchangers with small water channels, called microchannel coolers (MCC). This approach minimizes the distance between the heat source and the coolant, maximizing cooling efficiency. The use of MCCs demands a more complex cooling system than traditional air- and water-cooled packages because the electrical current and the cooling fluid must coexist within the cooler. Without proper design, corrosion and erosion can shorten the lifetime of the device.

AI2O3_unten_01Microchannel structures are made of thin copper foils that are bonded into a hermetically tight block. The specific microchannel structure determines the thermal resistance, pressure loss, and flow rate. The coolant usually flows in and out through openings at the bottom using interference fits over o-rings or screw fittings.

Liquid coolers are an ideal solution for high-power applications. The active cooling areas can be customized to the diode layout. Customized ceramic substrates provide high-performance electrical power management.

For highly efficient thermal management, Rogers uses a special bonding process to create its curamik® DBC (Direct Bond Copper) micro-channel coolers. DBC copper coolers consist of several layers of pure copper foil into which different, very fine structures are etched. An integrated DBC cooler includes several layers of structured copper foil and a top and bottom layer made of DBC substrates (Al2O3 or AlN). The etched copper layers form the 3D cooling structures. Find out more about Rogers’s unique substrates and coolers for laser diodes.

 

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