Coherent OBIS LG 355nm OPSL Laser System

The Coherent OBIS LG 355 is an OPSL laser capable of a maximum output power of 20mW of 355nm (UV-A) laser light. The laser system is made from high quality machined aluminum and has a mechanical beam shutter as well as an emission indicator LED on the front. On the back of the laser system is a DB-26 connector, mini USB connector, fan connector, and some status LEDs. The DB-26 connector on the back of the unit contains connections for power input, safety interlocks, and serial communication. The OBIS LG is a "self contained" laser much like the CUBE series of diode lasers from Coherent. This means that the laser head assembly contains all of the necessary driver and control circuitry to operate. Essentially, all that is needed to operate the OBIS LG laser system is an appropriate power input and a thermally controlled mounting surface such as a heatsink and fan or TEC. A separate external controller or driver is not a requirement. Coherent does make OEM controllers that can be used with this laser such as the OBIS scientific controller or OBIS remote control unit.

coherent OBIS LG 355 OPSL laser

coherent OBIS LG 355 OPSL laser connections

Removing 2 screws on each side of the cover (4 total) reveal the internal components of the OBIS LG. The actual laser diode and optical components are located under a metal cover that is soldered to the bottom circuit board. This optical cavity is hermetically sealed and filled with nitrogen gas. On the front of the sealed enclosure, there is an optical window that filters out infrared and green wavelengths of laser light and allow others to pass though. There are 3 total circuit boards contained within the OBIS LG laser system. The board that runs parallel to the optical cavity is the control and driver board which provides power to the pump diode and precise control over the temperature-sensitive components contained within the optical cavity. The boards mounted to the rear of the housing are responsible for power conversion (DC-DC converters) and interfacing/communications. In this particular unit, some thermal pads were installed between the DC-DC converters and metal casing to better transfer the heat and prevent overheating.

coherent OBIS LG 355 OPSL laser inside

Under the hermetically sealed cover are the actual optical components. The majority of the components are further protected by a metal casing, but some filtering optics and lenses can be seen at this point. Take note of the flat-flex ribbon cable that connects the diode and temperature control/sensing components to the bottom circuit board.

coherent OBIS LG 355 OPSL laser inside

Below is an image of the inner optical cavity. The colored lines correspond with the beam path. Being an OPSL laser, light emitted from the pump diode is filtered through a lens and then reflects off an OPS chip, converting the wavelength. The wavelength is further converted by both second and third harmonic generation optics that follow. It is worth noting that both 532nm and 355nm light is produced by this optical assembly, however, the 532nm (green) light is filtered out before it leaves the laser head. This results in 355nm as the only final wavelength emitted, which is the intent of this OBIS LG model.

coherent OBIS LG 355 OPSL laser inside

Here is an annotated image that clearly describes the beam path of the OBIS LG 355nm laser system.

coherent OBIS LG 355 OPSL laser beam path

The wavelength of light produced by this laser system is in the ultraviolet spectrum and is not visible to the human eye. Glow powders or other fluorescent substances/materials are the best way to view the laser output. Please be careful when operating units like this, lasers that operate outside of the visible light spectrum can still cause permanent eye damage, and are especially dangerous since you cannot easily see the beam. The beam becomes very bright and visible when aimed at a fluorescent sheet.

coherent OBIS LG 355 laser on fluorescent material

This is the OBIS LG diode driver and temperature control board. It supplies the necessary current to the laser diode in a controlled manner. It also regulates the temperature of the sensitive optical components.

coherent OBIS LG 355 laser driver board

Here are some pictures of the front and the back of the DC-DC converter board. There are two large capacitors as well which helps to smooth out the DC voltage.

coherent OBIS LG 355 laser dc-dc converter board coherent OBIS LG 355 laser dc-dc converter board

This board breaks out the DB-26 connector on the back of the laser head to the internal circuit boards. It also has a section that slots into a card connector on the bottom circuit board.

coherent OBIS LG 355 laser breakout board

Please check out Zenodilodon's detailed video about the Coherent OBIS LG 355nm OPSL laser. To learn more about OPSL lasers, visit the links below.