Dear Editor, first, we would like to thank the referee for the constructive comments. Referee comment: 1)As a criticism, I need to add that the study, while being sound and probably tedious to conduct, is of technical nature and does not convey or discuss novel physical insight. One thus may ask whether PRA is the right journal. Reply: The near-concentric cavity presented here exhibits the smallest cavity waist with a cavity geometry that is favourable for atom trapping experiments. In addition, the presented work carried out the mode analysis and demonstrated that the Gaussian beam theory remains valid in such strong focusing regime. This can provide a benchmark for theoretical work to investigate the breakdown of paraxial approximation in describing resonant modes of optical cavities. Hence, we believe that our work is interesting to the audience of PRA. 2) The authors motivate their cavity to be advantageous for scaling up cavity experiments, but the challenging operation (active 3D stabilization!) poses questions about benefits along this line Reply: The cavity alignment is automatically checked and the realignment procedure is also automatically done and takes only few seconds. Thus this does not affect the experimental duty cycle significantly. In addition, the need for transverse realignment is mainly caused by temperature changes. This work is only a first step of this approach. It takes the high-finesse cavity community more than 20 years to achieve the current state of the art (see Kimble Physica Scripta. Vol. T76, 127-137, 1998). We believe that the 3D stabilization is not a fundamental limit and there are feasible improvement which can be done in future designs to improve the passive stabilization. For example, the two cavity mirror holders can be made of materials with different thermal expansion coefficient (a1,a2) and have different lengths (l1,l2) such that l1*a1=l2*a2 to mitigate the transverse misalignment. 3) The authors state that near-concentric cavities exhibit the smallest mode waist; this should be specified more explicitly. The mode waist can become similarly small for smallest mirror separation. The waist size is symmetric with respect to the mirror separation and gets small for both short and long cavities. It is only by fine tuning the cavity length of the last mode closer to the stability than lambda/2 (e.g. by wavelength tuning) that one can get smaller than for l_cav = lambda/2. Reply: We agree with the referee's comment and removed the statement about the tightest focus of the cavity mode. We would like to note that it is theoretically true that both very short cavities and near-concentric cavities can obtain small cavity mode waists. However, the former can only achieve a diffraction-limited waist (~lambda/2) with an almost zero cavity length, which is technically difficult to achieve due to the penetration of the cavity field into the mirror coating, especially when the coating must be thick to obtain high finesse (Hood et al., 2001 PhysRevA.64.033804). In this work, from the measured cavity length we determined that the cavity mode waist is 2.4 micron, which is the smallest waist obtained so far for a cavity geometry that is favourable for atom trapping experiments to the extent of our knowledge. For a comparison with fiber-based cavities, see Brandstatter, B. et al., Review of Scientific Instruments 84, 123104 (2013). We include the above statement at the second paragraph, pg 4 in the manuscript. 4) The figure of merit for light matter coupling scales with Finesse / mode cross section (~Cooperativity), such that a microcavity and a near-concentric cavity with same mode cross section also require the same finesse (i.e. mirror reflectivity) for a given Cooperativity. So the argument is not quite correct to state that near-concentric cavities require less demanding coatings. On the other hand, the ratio of coupling strength over cavity decay rate does improve for a long cavity, and as long as the rates remain larger than the atomic decay, one can enter the strong coupling regime more easily. This should be described more clearly. Reply: It is true that the Cooperativity does not depend on the cavity length given a cavity mode cross section. However, that the Cooperativity is larger than one is only a necessary condition for the strong atom-cavity coupling. We are more interested in achieving the sufficient condition that g>>kappa and g>>gamma (gamma is the cavity decay rate). The ratio of g over gamma is proportional to F(L^1/2)/w, which is more favorable for longer cavity lengths at a given cavity Finesse and a cavity mode cross section. We include a corresponding statement at the second paragraph, first page of the manuscript: "The ratio of coupling strength over cavity decay rate is proportional to $F\sqrt{l_{cav}}/w$, which is more favorable for longer cavity lengths at a given cavity finesse $F$ and a cavity mode waist $w$." 5) An important argument is missing in my view: For ion trap experiments, large distance from the trapped ion to the dielectric mirrors is required to avoid trap deformation and heating. This is also a type of experiment where such rather unpractical cavities are used (e.g. in Innsbruck). Reply: At the second paragraph, page 1, we included a similar explanation of the advantage of using near-concentric cavities in ion trap experiments in the manuscript: "For use with trapped ions, the large separation between two mirrors provides the ability to avoid charging problems with dielectric surfaces, which has been a major hindrance to the development of ion traps in optical cavities" 6)Multimode cavity qed appears to be the most interesting direction where this could lead to; this could be emphasized and detailed a bit more. Reply: We will present the detailed studies of applications of multimode cavity qed somewhere else. 7)Space between words / sentences is sometimes missing Reply: We corrected the missing space. 8)The finesse of the cavity should be mentioned. The mode size at the mirrors should be mentioned for the last stable mode. Reply: We included the cavity finesse of F=603 and an inferred cavity mode waist at the mirror of 0.56 mm at the second paragraph of page 4 in the manuscript.