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Thorlabs DJ532 Laser Diode

Operating this add-on will required LD and TEC drivers. Check our tooling page for LD and TEC drivers that are within your reach.

Thorlabs provides small and cheap 40 mW DPSS laser diodes that have extremely narrow bandwidth but which requires a LD and TEC driver to operate. Here, we propose an upgrade that was successfuly tested to 12 cm-1 on the spectrum of isopropanol.

Assemble the module as below:

DJ532 Assembly

  1. Remove the front panel of the Thorlabs LDM21 and the sticky foam that is on the Peltier cooler. Degrease the Peltier using gentle acetone and cottons swabs. Let the acetone completely dry out before proceeding to the next steps.

  2. Check that the LD switch is on “AG” (Anode Grounded) mode and install the DJ532-40 laser with the middle pin oriented top.

  3. Install the o-ring in the groove of the #2020-12 (LD CLAMP) part. Set the clamp in place using two 2-56×1/2″ screws. If the screws are too long, use one or two washers. Do NOT overtighten the screws. The goal is to maintain the LD in contact with the TEC element without forcing on it.

  4. Re-mount the front panel of the LDM21 and place the laser assembly on the base plate using two 8-32×3/8″ DIN912 screws.

  5. Assemble the rest of the spectrometer according to the instructions of the Starter Edition.

Warning

always use ESD mat when handling the laser diode. Failing to do so will damage your DJ532-40 permanently

Operating a laser might not be trivial. Depending on the exact temperature and current you may experience either single or multiple longitudinal modes which can affects the performances depending on your slit size and sample type. This is illustrated in Figure 1 where you can you can observe the effect of both current (at a fixed temperature) or the effect of temperature (at two fixed currents) on my specific DJ532-40 laser diode. Each diode may behave differently but the results of Figure 2 should be considered typical for the DJ532-40.

Figure 1 - Graph of longitudinal modes variation with temperature and current

From Figure 1, we can summarize the following observations:

  • Changing the current within the operational range has the most drastic effect. You can see modes appearing and disappearing abruptly as you change the current. Sometimes the effect is progressive, as between 220 mA and 240 mA, or be very unstable, as when you go from 260 mA to 270 mA, or from 210 mA to 220 mA (still at 22.5°C).

  • Temperature change was found to be steadier here but still make a big difference since it can make your laser going from singlemode to multimode as can be seen by comparing 18°C and the range 21-25°C at 245 mA. Note that Figure 1 is basically obtained in these conditions.

  • Changing temperature does however not guarantee that you can alter the number of lasing modes as can be seen at 300 mA. At that current, which is near the nominal current to operate the laser at 40 mW, the spectral signature of the laser almost does not change on the 20-25°C temperature range.

Note that a 0.1 nm bandwidth coupled with a 15 µm slit is usualy sufficient for all liquid samples.