OPERATION
Temperature Control
12_06 LDM-4990 13
CHAPTER 2
(Peltier) devices provide a simple, reliable solution to precise temperature control
in many applications of optoelectronic devices. These solid-state devices can heat
or cool small thermal loads to more than 60°C from ambient and achieve
temperature stabilities of better than 0.001°C.
Active temperature control of the LDM-4990 is accomplished with two
thermoelectric modules and a temperature measurement element using a
thermistor for real-time feedback to a thermoelectric temperature controller such
as an ILX Lightwave LDT-5948. The actual temperature is measured by the
temperature sensor. This temperature is then compared to a set-point
temperature, to produce an error signal proportional to the difference between set-
point and actual temperature. The temperature controller outputs a proportional
bi-directional current to the thermoelectric modules depending on the direction of
the error.
Thermal resistance, measured in °C/W, between the laser package and the laser plate
results in a temperature difference between the laser plate and laser diode. The laser
plate is gold plated for better thermal conductivity. Caution must be used when placing a
laser diode in the mount and removing it not to scratch the surface between the laser
and the laser plate. Scratches and contamination of the surface will degrade the thermal
performance of the mount resulting in an increase of the thermal resistance between the
laser and laser plate.
Water Cooling
The LDM-4990 is configured for use as a natural or forced convection heat sink
using chilled water. Water cooling allows lowering the operating temperature of
the laser case to -20°C by providing higher heat dissipation than natural
convection.
Water cooling the 4990 is accomplished by attaching the brass water fittings
supplied in the shipping kit to the LDM-4990. A forced flow of 10°C water is
adequate for cooling the mount to -20°C. If higher performance is required, the
flow and/or the water temperature (through a chiller) can be adjusted.
Use caution when cooling the flow water below 10°C. Condensation may form on the
4990 housing and internal components.
To install water fittings, refer to Figure 2.8, and follow these steps:
1 Remove two black plastic hole plugs at the back of the mount on both sides of the 9-pin
connectors.
2 Apply teflon tape or a pipe sealant to the threads of each fitting, and thread them into the
