New Ultra-low Frequency Raman Filters Features and Applications

New Ultra-Low Frequency Raman Filters Features and Applications - Suitable for Ultra-low Wavenumber Raman Spectroscopy Measurements

Abstract: In many fields of scientific research, low-frequency Raman is an indispensable analytical tool. The Bragg Notch Filter is a unique Raman filter for ultralow-wavelength Raman spectroscopy. It can achieve Raman measurements up to 10cm-1. It is widely used in ultra-low frequency Raman. Spectrometers, therefore, such bulk grating Raman filters are also known as ultra-low frequency Raman filters.

      Ultra Low Frequency Raman Filter is a Raman filter which is widely used in low-wavelength Raman spectroscopy. It can achieve Raman spectroscopy measurement below 10cm-1. Shanghai Quanliang Optoelectronics is the main agent of this product.

      Ultra-low-frequency Raman filter (ULF) is a silicate photo-sensitive glass (PTR) material, which is produced by UV interferometric exposure. It consists of three ultra-narrow notch filters. It is composed of 1~2 narrow bandpass filters (Bandpass Filter). Both the bulk Bragg band-notch filter (BNF) and the bulk Bragg bandpass filter (BPF) belong to the same volume Bragg grating and they all play an important role in the measurement of low-wavelength Raman spectroscopy. Ultra-low frequency Raman filters (ULF) have other features that are far beyond standard Raman filters such as:

 Low-frequency Raman measurement down to 5cm-1 (single-stage spectrometer)

 Stokes and anti-Stokes Raman bands can be measured simultaneously;

 Strong environmental stability, free from humidity;

 No polarization sensitive characteristics;

 can withstand 400 high temperature;

    Ultra-low frequency Raman spectroscopy mainly uses Bragg bandpass filter (BPF) and Bragg narrow band-notch filter (BNF) two kinds of grating components, as follows we learn more about their characteristics:

(1) Prague Bandpass Filter (BPF)

      The Bragg bandpass filter (BPF) is mainly used for line width cleaning of the incident laser to remove the spectral noise of the laser and ensure that a good laser beam can be obtained. Standard bandpass filters typically have a bandwidth of 200-300cm-1, so spectral noise below 200cm-1 will affect ultralow-frequency Raman spectroscopy measurements. Our Bragg bandpass filter (BPF) bandwidth (FWHM) can be as low as 5cm-1, it can well remove the laser noise to 5cm-1, and the suppression ratio reaches -70dB.

Standard wavelengths: 488nm, 514nm, 532nm, 633nm, 785nm, and 1064nm (customized wavelengths: 405nm, 442nm, 458nm, 473nm, 477nm, 491nm, 502nm, 561nm, 660nm, 840nm, 1352nm, 1550nm, etc.)

 The bandwidth (FWHM) is less than 7cm-1;

 Reflectance: >90%;

 Standard size: 5mm x 5mm (large size can be customized);

Near diffraction-limited beam quality;

 Deflection angle: 20deg;

  Applications: Ultra-low frequency (THz) Raman spectrometer, beam filtering and clear noise, semiconductor Raman light source ASE filtering;

(2) Bragg Filter (BNF)

The Bragg Filter (BNF) can simultaneously measure Stokes and anti-Stokes Raman bands down to 5 cm-1 and achieve a transmission rate of up to 95%. The narrow-band notch filter also needs to satisfy the Bragg theory. For BNF with attenuated OD3, the deflection angle is 12 deg, and the FWHM acceptance angle is 6 mrad (about 0.3 deg). At present, the measurement of ultra-low frequency Raman spectra is mostly achieved using our ultra-low frequency Raman filter (ULF).

Standard wavelengths: 488nm, 514nm, 532nm, 633nm, 785nm, and 1064nm (customized wavelengths: 405nm, 442nm, 458nm, 473nm, 477nm, 491nm, 502nm, 561nm, 660nm, 840nm, 1352nm, 1550nm, etc.)

 Spectral bandwidth (FWHM): 5~8cm-1;

 attenuation value: OD3 or OD4;

 Standard size: 11mm x 11mm, 12.5mm x 12.5mm (1 inch Mount);

 Deflection angle: 12 deg;