DR-RINS: Digital real-time relative intensity noise suppressor for pump–probe spectroscopy and microscopy

Abstract

Relative intensity noise (RIN) inherent in fiber lasers poses a serious obstacle to their use in pump–probe spectroscopy and imaging. RIN can be removed through an analog balanced detector, or, as we have previously shown, software adaptive noise cancellation (ANC) on digitized signals. One major drawback to software ANC is the added time required for digitizing and post-processing. In this article, we describe a design for ANC on a field-programmable gate array (FPGA), making use of high-level synthesis tools and fixed-point arithmetic to achieve real-time laser RIN suppression at 25 MHz sample rates. Unlike the software-ANC approach, the FPGA-ANC device can serve as a dedicated drop-in denoiser, placed between the detectors and a commercial lock-in amplifier. We demonstrate its application to transient absorption spectroscopy and microscopy, lowering the noise floor to ∼17 dB above the shot noise limit. Furthermore, we demonstrate a dramatic improvement in data acquisition time from ∼6 h to ∼5 min in a real-time imaging scenario.

High-Repetition-Rate Transient Absorption Spectroscopy of Respiratory Supercomplexes

“…The dye can be removed with a mildly acidic destaining solution, but this makes it more difficult to locate protein bands within the gel. Though we were able to locate the more intense protein bands in destained gels using the transient absorption signal alone, we found this impractical for the weaker bands. Therefore, for consistency, we chose to perform all measurements directly on the dye-stained samples and numerically unmix the hemeprotein and dye signals (see below).…”

“…A balanced detector can effectively cancel RIN, but the rapid changes in transmissivity across a biological specimen require a high-bandwidth autobalanced detector to cancel RIN in a laser-scanning microscope . For these experiments, we use a digital adaptive filter implemented on a field-programmable gate array (FPGA) . The adaptive filter provides >10 dB gain in SNR, effectively allowing data to be acquired with a 200 ms LIA time constant that would otherwise require 3 s integration time.…”

“…14 For these experiments, we use a digital adaptive filter implemented on a field-programmable gate array (FPGA) . 15 The adaptive filter provides >10 dB gain in SNR, effectively allowing data to be acquired with a 200 ms LIA time constant that would otherwise require 3 s integration time.…”