Frequency measurements of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>2</mml:mn><mml:msub><mml:mi>ν</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>A</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:mrow><mml:mo>−</mml:mo><mml:msub><mml:mi>ν</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math> band transitions of methane in comb-referenced infrared-infrared double-resonance spectroscopy

Abstract

We carry out infrared-infrared double-resonance spectroscopy of the $2{\ensuremath{\nu}}_{3}{A}_{1}\text{\ensuremath{-}}{\ensuremath{\nu}}_{3}$ band of methane. Ten transitions of Q(1) to Q(4) are observed with an 88.5-THz difference-frequency-generation (DFG) source, while the lower levels are pumped through the ${\ensuremath{\nu}}_{3}$ band transition by another 90.5-THz DFG source phase-locked to an optical frequency comb (OFC). The transition frequencies are determined using the OFC with an uncertainty of 10 kHz, which is an improvement of 4 orders of magnitude compared with the previous studies.

Topics & Concepts