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Heat Sink for Pulsed Flash Illuminators

IP.com Disclosure Number: IPCOM000076107D
Original Publication Date: 1972-Jan-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Eros, S: AUTHOR

Abstract

In a pulsed GaAs diode used as a flash illuminator the average power applied to the diode, part of which is converted into heat, is applied during the pulse at such a high rate, that it cannot be conducted away by conventional heat-sinking fast enough to prevent the diode temperature from rising so high that laser operation becomes inefficient.

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Heat Sink for Pulsed Flash Illuminators

In a pulsed GaAs diode used as a flash illuminator the average power applied to the diode, part of which is converted into heat, is applied during the pulse at such a high rate, that it cannot be conducted away by conventional heat- sinking fast enough to prevent the diode temperature from rising so high that laser operation becomes inefficient.

The conventional one-sided heat sink, in which the diode is placed atop a copper header or other heat dissipating substrate, is ineffective. By considering the heat removal process in two stages, the first where heat is absorbed from the diode by a header which acts as a "heat sponge" and the second where the heat dissipates from the sponge, it has been found that a double header is much more effective. With this design, equilibrium is reached rapidly after the initiation of a pulse, the temperature remaining constant during the pulse. At the end of the pulse there is a relatively long off period, allowing the heat energy absorbed into the header to flow into the ultimate heat sink, such as liquid nitrogen.

For the conventional design, consider a laser diode of thickness d, width a, and length b, bonded to a heat sink having dimensions large compared to the diode dimensions. Assume that the junction is near the center of the diode.

The maximum temperature rise is calculated by summing the values of (1) the temperature rise due to heat generated in the junction as a transient term, plus a DC term using the average value of the heat produced in the junction; (2) the transient and DC terms due to heat uniformly generated in the bulk of the chip due to I R heating; and (3) the DC term in the heat sink, using the average value of the heat generated in the junction and bulk of the diode.

For one-dimensional heat flow into a medium due to a heat generated at a plane in the medium, the transient temperature rise is given by:

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Adding equations (1) and (4) obtains the transient rise in temperature during the 35 mus pulse; adding equations (3) and (5) obtains the total DC temperature rise. Summing the four equations obtains the equation: (6) sigma delta T = alpha W, alpha is the thermal resistance which, for a single-sided heats sink; has a value of 1.64 degrees K/W.

The optimization of I to obtain maximum diode output...