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Slit Width & f/# Matters

Providing the best match for sensitivity and resolution
Raman Spectrometers
Raman Software

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Balance Throughput vs Spectral Resolution

Optimize slit width and f/# for your Raman application

Spectrometer performance is fundamentally determined by throughput and resolution. Light collection efficiency scales with slit area and inversely with the square of the f/#, making low f/# designs especially valuable for fast Raman measurements. Wider slits further increase signal but reduce spectral resolution, creating the classic trade-off between throughput-and resolution. Configurable optical options allow you to select the best balance for your application – whether your priority is speed, sensitivity, or spectral detail.

Features & Benefits

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    Matching of throughput and spectral resolution to application priorities

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    Faster measurements and stronger signals with low-f/# optical designs

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    Selection of optimized slit and bench configurations

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    Proven 25 µm slit and f/1.3 configuration for most Raman applications

Match throughput and resolution with optimized Raman optics and configurations.

Slit Width and f/# Choice Impacts

 Choose the right combination of throughput, resolution and speed

Very narrow main peak of toluene recorded with f/1.3 X series system and f/2.0 XL system, both at 785 nm excitation, showing the additional detail resolved with the higher f/#.

f/# Influence

The f/# strongly influences how efficiently a spectrometer collects light. Wasatch’s flagship f/1.3 design maximizes throughput, making it the preferred choice for most Raman applications requiring strong signal and short acquisition times. The f/1.8 option maintains the same compact footprint while offering improved spectral resolution for applications where narrower FWHM is critical. Larger XL systems with scientific-grade detectors and f/1.5 or f/2.0 designs deliver even tighter resolution, typically for advanced applications where the XL’s performance justifies the additional cost.
Impact of slit width on signal and resolution

Slit Width

Slit width provides a second key adjustment for balancing throughput and resolution. Wider slits increase signal proportionally by admitting more light, while narrower slits improve spectral resolution, up to the practical limit imposed by the detector’s pixel size. Selecting the right slit width helps you to optimize the spectrometer’s performance without unnecessarily sacrificing speed. 
Typical Raman peaks from narrowest (left) to widest (right) versus a typical X series spectrometer resolution of 8 cm-1 FWHM

Resolution

Spectral resolution is important, but often over-specified. For most applications, the important Raman features are significantly broader than the spectrometer’s resolution. Once the instrument resolution is sufficiently below the width of the Raman lines of interest, tightening further only reduces the signal without an analytical benefit. 
Trade-off between resolution and Raman signal for different slit widths, for the example of WP 532X Raman systems.

Standard Slit Size

For most applications, Wasatch recommends a 25 µm slit as the optimal balance between throughput and spectral resolution across X, XL, and XM systems. A 15 µm slit may offer modest additional resolution improvement when required, while 50 µm can increase throughput for signal-limited measurements. For the compact XS platform, the integrated 20 µm slit is the optimum for the overall system performance.

 

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Misty Johnson

Misty Johnson is responsible for taking care of our grating customers at the Logan, Utah, facility. She has been a member of the Wasatch Photonics team since 2009. By understanding her customers’ needs and goals, as well as the current grating market, Misty is able to provide a superior level of customer support. As Account Manager, she acts as a liaison between customers and Wasatch Photonics’ manufacturing department making sure that the lines of communication are always open.

Customer support is an integral part of Wasatch Photonics commitment to customers. Whether you are in the market to purchase a single grating, inquiring as a distributor, or purchasing large volume, Misty will guide you seamlessly through the custom design process. Misty strives to build trust and strong long term relationships with Wasatch Photonics customers. She brings 20 years’ experience as customer support manager from a number of manufacturing and service companies.