Tunable Laser Diode Absorption Spectroscopy (TLDAS) with DBR Lasers

John Spencer About The Author

Thu, Aug 04, 2011 @ 11:35 AM

One of the main applications of Photodigm DBR lasers is absorption spectroscopy.  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.  Tunable laser diode absorption spectroscopy (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 DBR lasers 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. 

Each Photodigm Spectroscopy Series laser diode is supplied with a tuning curve showing the individual performance of that laser.  A typical example is shown in  Figure 1.   A Rb absorption curve recorded with a typical Photodigm DBR laser is shown in Figure 2.  

DBR laser tuning curveFigure 1.  Temperature tuning coefficient of a Photodigm DBR laser.  This laser will probe the Rb D2 resonance line at around 25.5 deg C.  Each Spectroscopy Series laser is provided with its characteristic tuning curve.   
Rubidium spectrum resized 600Figure 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 laser diodes over the wavelength range of 700 nm to 1100 nm.  Among the species of interest for tunable diode laser 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. 

For further information about all the wavelengths available, please contact Photodigm


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