anyone recognizes this laser diode? - Page 1
Forum section: electronics / beginners

author: chands
author_rank: Newbie
timestamp: August 24, 2025, 07:33:53 am
content: Dear All,We want to replace a bad laser diode inside an aerosol particle instrument CPC 3787. This is a TO-can 3-pin laser diode, with diameter 5.6 mm and height 3.6 mm. It is marked 5FGY B235 (pic attached).We checked the voltages between pins. The voltage between pin 2 and pin 1 (V(2)-V(1)) read 2 V. the voltage between pin 2 and pin 3 (V(2) - V(3)) read 4.45 V. So it is an N-type laser diode, with operational voltage about 2 V. We it was still working (although getting bad), the instrument showed that the laser current was 23 mA.However, we have no idea about other parameters such as wavelength and power output.Anybody recognizes this kind of laser diode?Many thanks!

author: ME
author_rank: Frequent Contributor
timestamp: August 24, 2025, 10:08:29 am
content: Why not tell us what its from for a start ,its a standard form factor but we need more info to help!.

author: chands
author_rank: Newbie
timestamp: August 24, 2025, 02:25:44 pm
content: thanks. I modified it a bit to include more info

author: ME
author_rank: Frequent Contributor
timestamp: August 25, 2025, 05:23:24 am
content: Will this help?

author: chands
author_rank: Newbie
timestamp: August 25, 2025, 05:36:49 am
content: Thanks. We have this manual. We did not find the specifications of laser diode in it. They determined not to release such information years ago.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 25, 2025, 08:55:23 am
content: There is a hint to the diode-specs in the laser safety warning label on page 9:650nm @ 5mW max@ Thorlabs you'll find the outlines of common LD. Yours should be Ø 5.6mm

author: chands
author_rank: Newbie
timestamp: August 25, 2025, 03:01:17 pm
content: Many thanks! An expert just told us that laser diodes have typical voltage ranges by wavelengths. 2 V operational voltage indicates 630 - 670 nm (red). We have been thinking about the power. Now I think we have the answer.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 25, 2025, 03:51:49 pm
content: Tunable wavelenght by voltage? That's new.Your manual states something, that LD's output ins not only monitored by current they have an additional detector. If such component is not seen in the optical compartment i argue, the third pin of the LD is the output of an monitor-diode. Could be important at your order...

author: chands
author_rank: Newbie
timestamp: August 26, 2025, 05:55:30 am
content: Thank you! We will certainly consider this factor.

author: ME
author_rank: Frequent Contributor
timestamp: August 26, 2025, 07:58:22 am
content: throw in a red ld in it and try it.

author: mikerj
author_rank: Super Contributor
timestamp: August 26, 2025, 08:42:35 am
content: Quote from: Uunoctium on August 25, 2025, 03:51:49 pmThe forward voltage has a wavelength dependency (for basic lasers without frequency doublers etc.) because of the bandgap energy. Have you never noticed something similar with LEDs?

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 26, 2025, 03:59:12 pm
content: This occurs within a narrow band that is no more than a fraction of a nanometer, as shown in Fig. 2, and the proven countermeasure is a regulated TEC.https://www.teamwavelength.com/download/applicationtechnotes/an-ld18.pdf

author: TimFox
author_rank: Super Contributor
timestamp: August 26, 2025, 05:07:07 pm
content: Fig 2 in the app note shows the slight dependence of wavelength on junction temperature for a given laser device.However, when selecting devices, different semiconductor materials, each with its own band gap, will have a different natural wavelength and color, and require a different forward voltage to conduct substantial current and emit photons. Basic quantum effect in solid-state physics and engineering.