Single-fiber-laser-based wavelength tunable excitation for coherent Raman spectroscopy

Abstract

We demonstrate coherent Raman spectroscopy (CRS) using a tunable excitation source based on a single femtosecond fiber laser. The frequency difference between the pump and the Stokes pulses was generated by soliton self-frequency shifting (SSFS) in a nonlinear optical fiber. Spectra of C-H stretches of cyclohexane were measured simultaneously by stimulated Raman gain (SRG) and coherent anti-Stokes Raman scattering (CARS) and compared. We demonstrate the use of spectral focusing through pulse chirping to improve CRS spectral resolution. We analyze the impact of pulse stretching on the reduction of power efficiency for CARS and SRG. Due to chromatic dispersion in the fiber-optic system, the differential pulse delay is a function of Stokes wavelength. This differential delay has to be accounted for when performing spectroscopy in which the Stokes wavelength needs to be scanned. CARS and SRG signals were collected and displayed in two dimensions as a function of both the time delay between chirped pulses and the Stokes wavelength, and we demonstrate how to find the stimulated Raman spectrum from the two-dimensional plots. Strategies of system optimization consideration are discussed in terms of practical applications.

Shedding new light on lipid functions with CARS and SRS microscopy

“…Fiber lasers for CRS systems are currently being developed for widespread use, and several groups have included them in CARS microscopy. However, higher laser noise from existing fiber lasers precludes their use in SRS microscopy at the moment [46–51]. …”

Stimulated Raman spectroscopy using chirped pulses

“…In Hellerer's version of spectral focusing, the same amount of temporal chirp is added to broadband Stokes and pump pulses, which have different central wavelengths. Using chirped pulses for CARS microscopy has been implemented in many different systems . For instance, Pegoraro et al .…”

“…Using chirped pulses for CARS microscopy has been implemented in many different systems. [9][10][11][12][13][14][15][16][17][18][19][20] For instance, Pegoraro et al have used it to image live cells and tissues, and Borri and coworkers have developed a method to use spectral focusing for CARS microspectroscopy. [14][15][16] In this paper, we present the theory and experimental results for a new method of using chirped pulses for SRS, which we termed chirped-pulse-SRS (CP-SRS, Fig.…”

Divided pulse soliton self-frequency shift: a multi-color, dual-polarization, power-scalable, broadly tunable optical source

“…We benchmarked the source by recording the relationship between single-pulse soliton energy and the frequency shift of the resultant output pulse [1–6]. An Andor spectrometer (SR-500i-A-R) with an InGaAs IR camera (iDus InGaAs 490A-1.7) was used to measure the output pulse spectrum.…”

“…The power scalable design of the DPS source decouples the center wavelength and the output pulse power, making it an appealing excitation source for many applications and, specifically, for nonlinear optical imaging methodologies [6,26–32]. The ability of the optical imaging instrumentation to penetrate deeper into biological tissue and to provide greater sample selectivity provide two capabilities that have enabled significant growth in the biological and biomedical fields.…”