We have measured the electronic absorption spectrum of the oxygen (O2) A band , near 760 nm in room air by using a newly available external-cavity diode laser. The external-cavity diode laser permitted a continuous, single-mode scan of the P branch of ambient oxygen by 2f modulation spectroscopy. The external-cavity diode laser opens up many applications limited in the past by the noncontinuous tunability of standard monolithic Fabry–Perot cavity laser designs. Specifically, absorption transitions that coincide with the gain bandwidth of any available diode laser (635 to 1550 nm) may now be reached without the problems and limitations imposed by mode hops inherent in standard Fabry–Perot cavity designs.
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