# Laser-Assisted Etching of EagleXG Glass by Irradiation at Low Pulse-Repetition Rate  
[PERSON]  
1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] 32, I-20133 Milano, Italy; [EMAIL_ADDRESS] (R.M.); [EMAIL_ADDRESS] (M.B.)1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] 32, I-20133 Milano, Italy; [EMAIL_ADDRESS] (R.O.); [EMAIL_ADDRESS] (F.B.)1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] 32, I-20133 Milano, Italy; [EMAIL_ADDRESS] (R.M.); [EMAIL_ADDRESS] (M.B.)1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] 32, I-20133 Milano, Italy; [EMAIL_ADDRESS] (R.O.); [EMAIL_ADDRESS] (F.B.)1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] 32, I-20133 Milano, Italy; [EMAIL_ADDRESS] (R.O.); [EMAIL_ADDRESS] (F.B.)1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] 32, I-20133 Milano, Italy; [EMAIL_ADDRESS] (R.O.); [EMAIL_ADDRESS] (F.B.)1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] 32, I-20133 Milano, Italy; [EMAIL_ADDRESS] (R.O.); [EMAIL_ADDRESS] (F.B.)1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] 32, I-20133 Milano, Italy; [EMAIL_ADDRESS] (R.O.); [EMAIL_ADDRESS] (F.B.)1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] 32, I-20133 Milano, Italy; [EMAIL_ADDRESS] (R.O.); [EMAIL_ADDRESS] (M.B.)1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] 32, I-20133 Milano, Italy; [EMAIL_ADDRESS] (R.O.); [EMAIL_ADDRESS] (F.B.)1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] 32, I-20133 Milano, Italy; [EMAIL_ADDRESS] (R.O.); [EMAIL_ADDRESS] (M.B.)1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] 32, I-20133 Milano, Italy; [EMAIL_ADDRESS] (R.O.); [EMAIL_ADDRESS] (F.B.)1 Dipartimento di Fisica, Politecnico di Milano, p.za [PERSON] da Vinci 32, I-20133 Milano, Italy; roberto.mosellame@ifn.  
refractive index contrast in a fused silica substrate is not a trivial task, requiring special fabrication techniques and long fabrication times [11; 12; 13]. This impacts on the overall design complexity of integrated optofluidic devices realized by FLM.  
On the other hand, waveguides with high index contrast and low propagation losses have been demonstrated in commercial borosilicate glasses, such as Eagle2000 and EagleXG (Corning Inc., Corning, NY, USA) [14; 15; 16] or AF45 (Schott AG, Mainz, Germany) [17]. These have enabled the demonstration of elaborated 3D optical circuits with applications encompassing quantum information experiments [18; 19], astrophotonics [20], and telecommunications [21]. The application of the FLICE microstructure technique to these glasses would disclose a great potential for the fabrication of optofluidic devices, where complex interferometers [18; 22] could be integrated monolithically with a microfluidic network.  
Laser-assisted etching in borosilicate glasses has been marginally investigated to date. First studies failed to find relevant etching selectivity of the laser-irradiated tracks in these substrates [4]. More recently, laser-assisted etching with HF and KOH was demonstrated in EagleXG glass [23], but by adopting very high scan speeds for the laser irradiation (in the order of 50-100 mm/s), which can be problematic in the inscription of minute details or when using advanced shape-control techniques [24]. Other works assessed favourable etching selectivity in KOH solutions for Pyrex (Corning 7740) [25] and Borofloat 33 (Schott) [26] glass; however, complex optical circuits have not been demonstrated, as to now, in these substrates by FLM.  
In this work, we advance the experimental investigation of the FLICE technique in the EagleXG (Corning) glass, employing both HF and KOH etching solutions. By exploring a large set of irradiation parameters, we find convenient conditions showing high etching selectivity, for a pulse repetition rate of 25 kHz and translation speeds in the order of 1 mm/s, which are compatible with the inscription of elaborated patterns.