This page contains information on operating the semiconductor laser set-up in H040.

General information

The set-up consists of a light-tight enclosure with a movable X-Y stage for the Device Under Test (DUT). The three lasers are small diode lasers with a wavelength of 660, 980 or 1060 nm and a maximum output power of about 1 mW. The output of the laser is guided via an optical fibre and focuser (spot size 9 um) to a movable Z-stage.

Laser Safety

All three lasers are class IIIb lasers which means that directly looking into the laser beam can lead to permanent damage of the retina. Quoting Wikipedia: A Class 3B laser is hazardous if the eye is exposed directly, but diffuse reflections such as from paper or other matte surfaces are not harmful. Continuous lasers in the wavelength range from 315 nm to far infrared are limited to 0.5 W. For pulsed lasers between 400 and 700 nm, the limit is 30 mW. Other limits apply to other wavelengths and to ultrashort pulsed lasers. Protective eyewear is typically required where direct viewing of a class 3B laser beam may occur. Class-3B lasers must be equipped with a key switch and a safety interlock.

Our set-up is protected with an interlock on the door of the enclosure which switches off the electrical signal (pulse) to the laser driver. Laser glasses are available in case you must work with the laser on while the door is open (bypassing the interlock). This is however only allowed after consulting a permanent staff member of the R&D group. Note that different laser safety glasses are needed for the different laser wavelengths: red light: 660 nm or infrared light: 980 and 1060 nm

List of Components

Needed:
  • Lighting
  • 2nd focuser when splitter is used
  • Interlock

Movable stages

All 3 axes are controlled via the Micos SMC-Corvus motion controller. The Corvus has two different operating modes: manual and terminal, which both speak for themselves. For manual mode, the joystick needs to be attached on startup, and for terminal mode, the Corvus needs to be connected to a computer via the RS323 connection on the back. For this connection you need to know a few settings:

  • Baudrate: depends on the first two switches on the back (see manual)
  • Data bits: 8
  • Stop bits: 1
  • Parity: None
  • Flow control: None
The computer can send commands of the serial port via e.g. PuTTY or any other program that sends commands to the serial port of the computer. These commands must be sent in the command language for the Corvus called Venus. See below for a few useful commands.

Useful Venus commands

Checking status of the Corvus

ge: returns any error that was encountered
gme: returns any machine error that was encountered
st: returns the status of the Corvus in a decimal number, for further explanation see manual

Calibrating the motion stages

cal: moves the axes to the furthest negative position until they reach their cal-switch, this now is 0, 0, 0
rm: moves the axes to the furthest positive position until they reach their rm-switch, this sets the range in which the stages can move

Moving the motion stages
NOTE: on startup the "brake" on the z-axis is active, to disable this brake use 1 1 setsout and to enable it again 0 1 setsout
NOTE: Ctrl+c in PuTTY will always stop the current move

delta_x delta_y delta_y r: moves the stages relative to the current position, e.g. 1000 0 -10 r
x y z m: moves the stages to coordinate x, y, z

Further useful commands

0 j: disables manual mode
1 j: enables manual mode
-1 getswst: returns the state of the 6 switches (cal + rm switch per axis)
-1 getunit: returns the unit of each axis (nm, Ám, etc.)

Programs to take data and control the motion stage

On Anthias there is a folder with a bunch of python scripts to control the motion stage and take data. These scripts are located in /home/ptr/Desktop/CorvusController/Scripts. Below, a list of scripts and their usage is given. To execute the scritps go to this directory and type: python3.6 MYSCRIPT.py, where you replace MYSCRIPT.py with the name of the script you want to execute.

Send commands to the Corvus
Like the name says, this command sends the commands that you type to the Corvus, much like PuTTY would do. It is named terminal.py. When the program is started it askes for a command, after pressing enter it sends it to the Corvus. Type "exit" to quit the program.

Scan z-axis to find focus point of the laser
This program is called z_scan.py, and takes 5 arguments. These arguments can be found by typing z_scan.py help. It takes the minimum z_value with respect to the starting position, the maximum value (THIS SHOULD ALWAYS BE 0!), the size of the steps to take, time to measure, and the folder with respect to /localstore/TPX3/DATA/CHIP0/Test/ to place the measurements in (put '' if you do not want a extra folder, and make sure the folder exists before you run the program).

Error codes encountered in the past

Machine error code 10: faulty 12V power supply
This error code showed up along with status (st) 136. This error code resulted in the motors not being powered, and the switches in on state. The origin of the error really was a faulty power supply. On the PCB in the Corvus, a diode had broken, which resulted in a shorted 12V power supply. The solution was to replace this diode (SB360-E3/73). The switching regulator (LM2575HVT-12) could be replaced as well, however this is not necessary to do.

Details about lasers

Pulse Generator for Laser

The lasers need an input signal from e.g. a pulse generator to start lasering. For this, the Agilent 33220A can be used if the pulse length is above ~20ns. Make sure that the output impedance on the pulse generator is set to 25Ω if a splitter is used to view the pulse on an oscilloscope.

Topic attachments
I Attachment Action Size Date Who Comment
PDFpdf DY3.pdf manage 104.5 K 2011-11-15 - 17:42 MartinVanBeuzekom  
PDFpdf FG1.pdf manage 96.9 K 2011-11-15 - 17:50 MartinVanBeuzekom  
PDFpdf collimators_focusers.pdf manage 413.8 K 2012-03-12 - 15:19 MartinVanBeuzekom  
JPEGjpg laser_spec_1060nm.jpg manage 360.3 K 2012-03-09 - 12:55 MartinVanBeuzekom  
JPEGjpg laser_spec_660nm.jpg manage 304.9 K 2012-03-09 - 12:54 MartinVanBeuzekom  
JPEGjpg laser_spec_980nm.jpg manage 425.5 K 2012-03-09 - 12:55 MartinVanBeuzekom  
PDFpdf laser_spotsize_etc.pdf manage 387.0 K 2012-03-12 - 15:19 MartinVanBeuzekom  
Topic revision: r12 - 2018-11-26 - RobbertGeertsema
 
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