Replacing the 650nm laser diode with a 850nm laser diode

[Tymon H]

Hello everyone! I am looking to replace the laser diode with one of a higher wavelength. The initial design uses the VLM-650-03-LPA-ND which has the corresponding specs:

VLM-650-03-LPA-ND

Wavelength 650nm

Voltage - Input 2.6V ~ 5V

Current Rating (Amps) 40mA

Power (Watts) 2.5mW

I am looking at replacing the laser with either the VLM-850-03LPT-ND or the VLM-850-03LPA-ND. Both of these lasers have the same diameter and connectors as the original (VLM-650-03-LPA-ND) and hence will fit nicely into the chamber housing and OD board. The specs for each laser is given below:

VLM-850-03LPT-ND

Wavelength 850nm

Voltage - Input 2.6V ~ 5V

Current Rating (Amps) 30mA

Power (Watts) 1mW

VLM-850-03LPA-ND

Wavelength 850nm

Voltage - Input 2.6V ~ 5V

Current Rating (Amps) 30mA

Power (Watts) 3mW

As you can see from the specs given the power for each laser varies, will these lasers still be able to run from the original OD board and if so which would you recommend? 

Side Note: I am aware that the original light to frequency converter (TSL235R) is not temperature compensated for wavelengths above 700nm and hence I am expecting around 500 ppm/C (0.05% per degree). If anyone knows of a light to frequency converter that will fit with the original klavins layout but is temperature compensated at 850nm please let me know.

Thanks :) 

[Chris Takahashi]

It should probably work.  If its too bright and starts to saturate you can solder a resistor (probably on the order of 5-50 ohms) on R6 and hook the laser to pins 2,1 instead of 2,3 to further dim the laser. 

I also wouldn't worry about temperature compensation either. for one the measurement is normalized by the transmitted laser light measured by a second sensor which will have similar drift.  Also there are so many other error/noise sources that drown out the 500ppm/C. I would however recommend letting the system warm up for a few hours before blanking. 

[Tymon H]

Thanks Chris for the quick reply, I will go ahead and try the design with one of the new lasers, hopefully everything works as planned. Will update this discussion with the results when I have them.