The OSA software ships with HITRAN line-by-line references for acetylene (C2H2), water vapor (H2O), and carbon dioxide (CO2), and can import additional references downloaded from the HITRAN database. The predictions can be fit to the measured trace for comparison, and fits using mixtures of gases are supported. Narrowband Light SourceA DFB laser diode emitting at 1550 nm (193.7 THz) was used as a narrowband light source and measured with an OSA203C in both CW and pulsed operation. Figure 1: Measured interferograms and spectra for a narrowband light source in CW (Top) and pulsed at 20 kHz (Bottom)operation. Several key functions are explained in the Tutorial Videos tab. The intensity is mapped in a logarithmic scale. OSA settings: High Resolution, High Sensitivity, No Apodization, 5 averages.
Robust graph manipulation tools include automatic and manual scaling of the displayed portion of the trace and markers for determining exact data values and visualizing data boundaries. The filter bank scheme was shown to provide more speech information than the zero-crossing scheme. Click to EnlargeNoise Floor in Absolute Power ModeAbsolute Power mode is recommended for narrowband sources. Instead the minimum hold function was used for 5 sets of spectra from the four different sensitivity settings. Check out the video after the break to see the VU in action, and a second video that gives some details on the hardware build. When [Dooievriend] set out to design the audio analyzing portion of the firmware, his mind jumped to the discrete Fourier transform.
All of Thorlabs’ OSAs accept FC/PC-terminated fiber patch cables and collimated free-space beams up to Ø6 mm. See the Gas Spectroscopy tab for an example setup. Click to EnlargeAbsolute Power mode is recommended for narrowband sources. This was expected as the 85 MHz repetition rate of the laser is well beyond the 40 kHz bandwidth of the OSA’s detectors.