Abstract-We demonstrate near-infrared cavity-enhanced optical frequency comb spectroscopy of R branch of CO2 overtone transitions around 1.57µm. The measurement setup is based on an Er:fiber optical frequency comb, high finesse cavity and a VIPA spectrometer.A dither locking scheme provides robust operation and high absorption sensitivity enhancement, while a VIPA etalon-based spectrometer provides rapid broadband acquisition with 600 MHz spectral resolution. The sensitivity of the system reaches 2.3×10 -9 cm -1 at 2×82s acquisition time. We verify the resolution of the experimental setup by comparing the measured spectrum with the high-quality spectrum obtained with a cavity ring-down spectrometer.With the development of optical frequency comb (OFC) at the turn of the millennium the optical absorption spectroscopy obtained a versatile tool for frequency measurements [1][2][3]. When used directly to interrogate an atomic or molecular sample, the broadband spectrum of optical frequency comb offers high sensitivity in a wide spectral range, with acquisition time of the order of seconds or lower. It removes the need for stepwise tuning of a continuous wave (cw) laser, allowing to sense the absorption of tens of molecular lines simultaneously and minimize the influence of long term drifts.Multiple approaches have been demonstrated with this technique until now [4][5][6], including cavity ring-down spectroscopy [7], dual-comb spectroscopy [8][9][10], cavityenhanced Fourier Transform Spectroscopy [11,12] or noise immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) [13]. In cavityenhanced measurements, the overlap between OFC and cavity modes is ensured by two approaches: tight lock usually performed by two-point Pound-Drever-Hall technique [11,14] and so called 'dither lock', where the cavity length is modulated so that the OFC and cavity resonances periodically coincide [15,16]. As shown before [4,17], the first approach offers the highest transmitted power and enhancement of the effective optical length (L eff =βF/π L, where F is the cavity finesse, L -the cavity length and β -an enhancement factor equal to 2 in this case), putting high demands on locking speed. The requirements of the second approach are much lower * E-mail: gkowzan@fizyka.umk.pl at the price of lower transmission and decreased effective optical length depending on locking settings. In all mentioned setups multiple approaches were used to disperse an optical frequency comb spectrum [4][5][6]. Spectrometers consisting of a virtually imaged phase array (VIPA) etalon [18][19][20], a diffraction grating and a camera are attractive because they provide rapid acquisition, limited only by the camera speed, in a compact package without any moving parts. So far, none of the presented frequency comb VIPA spectrometers have managed to combine cavity-enhanced sensitivity, broad spectral coverage, high signal-to-noise ratio, rapid acquisition and self-referenced frequency axis. This paper presents such a system built out of off-the-shel...