A six-octave optical frequency comb from a scalable few-cycle erbium fiber laser

TL;DR

This paper presents a scalable erbium fiber laser that generates a six-octave optical frequency comb spanning ultraviolet to mid-infrared, enabling advanced spectroscopy and microscopy applications with high spectral resolution.

Contribution

The authors demonstrate a robust, low-noise erbium fiber laser producing near-single-cycle pulses that generate a six-octave frequency comb through second-order nonlinearities, a significant advancement in laser technology.

Findings

Six-octave spectral coverage from UV to mid-IR achieved

Frequency comb with 10 kHz linewidth at 193 THz demonstrated

Spectral resolving power exceeding 10^10 across 0.86 PHz bandwidth

Abstract

A compact and robust coherent laser light source that provides spectral coverage from the ultraviolet to infrared is desirable for numerous applications, including heterodyne super resolution imaging[1], broadband infrared microscopy[2], protein structure determination[3], and standoff atmospheric trace-gas detection[4]. Addressing these demanding measurement problems, laser frequency combs[5] combine user-defined spectral resolution with sub-femtosecond timing and waveform control to enable new modalities of high-resolution, high-speed, and broadband spectroscopy[6-9]. In this Letter we introduce a scalable source of near-single-cycle, 0.56 MW pulses generated from robust and low-noise erbium fiber (Er:fiber) technology, and we use it to generate a frequency comb that spans six octaves from the ultraviolet (350 nm) to mid-infrared (22500 nm). The high peak power allows us to exploit the second-order nonlinearities in infrared-transparent, nonlinear crystals (LiNbO$_3$, GaSe, and CSP) to provide a robust source of phase-stable infrared ultra-short pulses with simultaneous spectral brightness exceeding that of an infrared synchrotron[10]. Additional cascaded second-order nonlinearities in LiNbO$_3$ lead to comb generation with four octaves of simultaneous coverage (0.350 to 5.6 $\mu$m). With a comb-tooth linewidth of 10 kHz at 193 THz, we realize a notable spectral resolving power exceeding 10$^{10}$ across 0.86 PHz of bandwidth. We anticipate that this compact and accessible technology will open new opportunities for multi-band precision spectroscopy, coherent microscopy, ultra-high sensitivity nanoscopy, astronomical spectroscopy, and precision carrier-envelope phase (CEP) stable strong field phenomena.