Tunable Laser Diode Absorption Spectroscopy


Using Photodigm DBR Lasers for TLDAS

One of the main applications of Photodigm DBR lasers is tunable laser diode absorption spectroscopy (TLDAS).  In this application, the laser is tuned by varying either current or temperature to sweep the narrow bandwidth output across an absorption line of a species of interest.  Laser diode spectroscopy by TLDAS can be used to establish a precise frequency reference when the laser output is locked to an atomic transition.  Because these electronic transitions are sensitive to minute perturbations in their physical environment, these frequency references can be used as the basis for atomic clocks, gyros, magnetometers, and gravimeters. TLDAS can also be used to monitor changes in concentration of absorption species, such as O2 or I2

Photodigm tunable laser diodes are precisely tunable by varying either current or temperature.  Tuning coefficients are approximately 0.06 nm/C  (25GHz/ deg C) by temperature or  0.003 nm/mA (1 GHz/mA) by current.  With a linewidth of a MHz or less,  and a side mode suppression of greater than 30 dB, the Photodigm DBR laser is able to effectively probe a variety of atomic and molecular species. 

Photodigm DBR lasers are designed with specific applications in mind.  Spectroscopy-Certified™ laser diodes  are designed to be resonant with a specific spectroscopic transition.  Applications-Certified™ lasers are certified to meet stringent applications driven specifications.  These specs include wavelength, mode-hop free tuning range, power, and noise level.  

Each Photodigm device is supplied with a tuning curve showing the individual performance of that laser.  A typical example is shown in  Figure 1.   An absorption curve for Rb recorded with a Rb certified laser is shown in Figure 2.  

Temperature characteristic of tunable laser diodeFigure 1.  Temperature tuning coefficient of a Photodigm DBR laser.  This laser will probe the Rb Dresonance line at around 25.5 deg C.  Each Spectroscopy Certified laser is provided with its characteristic tuning curve.   
Laser spectroscopy of Rubidium

Figure 2. Rb absorption spectrum recorded using a Photodigm 780 nm DBR laser tuned over a 7 mA range. 

Photodigm produces its Spectroscopy Series of DBR tunable laser diodes over the wavelength range of 700 nm to 1100 nm.  Among the species of interest for tunable laser diodes absorption spectroscopy in this range are the following:  

      • O2: multiple absorption lines between 760 to 765 nm
      • K:  767, 770 nm
      • Rb:  780, 795 nm
      • Cs:  852, 895 nm
      • Metastable He:  1083 nm
      • I2:  multiple lines  

Photodigm tunable diode lasers have earned a reputation for stability and performance in this application.  

For more information about tunable laser absorption spectroscopy, please download our Applications Note: Rubidium Absorption Spectroscopy