1. What problem do NoiseBlock™ ASE filters solve?

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NoiseBlock™ ASE filters eliminate the broadband amplified spontaneous emission (ASE) that accompanies the narrow laser line in many diode and DPSS lasers. By removing this unwanted background, they enhance signal‑to‑noise performance in applications such as ultra‑low‑frequency/THz Raman, telecommunications, and optical sensing. They are especially effective in systems where weak signals lie close to the excitation wavelength and require strong suppression of background fluorescence and ASE. NoiseBlock™ designs can reduce ASE by more than 70 dB while maintaining the integrity of the desired laser spectrum.

 

2. What product styles are available?

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Items below are often paired with our SureBlock™ ultra‑narrow notch filters for low‑frequency Raman.

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• Reflective ASE Suppression Filter (standard): High diffraction efficiency (>90% typical) at the design wavelength with narrow spectral HWHM <10 cm⁻¹. Often paired with our SureBlock™ ultra‑narrow notch filters for low‑frequency Raman.

• Reflective 90/10 Beamsplitter (BS) Filter: Diffracts ~90% of the laser line and transmits nearly all non‑laser wavelengths, enabling recovery of both Stokes and Anti‑Stokes Raman and up to ~4× signal boost versus a broadband 50/50 splitter in typical layouts.    

• Transmissive Ultra‑Narrow Bandpass ASE Filter: Engineered for ease of implementation in transmission; achieves OD4 at ~9–10 cm⁻¹ as a single unit and >OD8 when two are cascaded-while maintaining high in‑band transmission (>85%).

 

3. How do the reflective and transmissive filters differ in practice?

 

Integration path:

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• Reflective: Works by diffracting (reflecting) the laser line at the Bragg condition while transmitting the broadband ASE away; requires managing the shallow diffracted angle (2θ ~8–12° typical). Space constraints and difficulty in aligning cascaded geometries are important considerations. Mirror mounts are often necessary to obtain the alignments necessary.

• Transmissive: Passes the laser line and blocks nearby ASE in transmission, simplifying beam routing and housing.    

   

Beam handling & aperture:

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• Reflective: Larger clear apertures are available (e.g., 4.5 mm in ½″ mount for ASE filters; 9 mm in 1″ for 90/10 BS). Better for larger beams.       

• Transmissive: Compact form factor; typical 2.5 mm clear aperture in ½″ mount-best for well‑collimated, smaller beams.

   

Polarization sensitivity:

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• Reflective: Not polarization sensitive in typical use case diffraction angles

• Transmissive: Polarization sensitive. Element must be oriented according to laser polarization orientation. Can also be used to improve polarization extinction ratio.  

 

 

4.  How many ASE filters are required? 

 

This is application and laser source dependent. Clean DPSS and gas lasers may work fine for strong Raman samples with only a beamsplitter element. Weak Raman or highly reflective samples may require additional ASE. Semiconductor lasers generally require at least 2 ASE filters. Fiber coupled lasers may introduce additional requirements to clean up signal generated within the fiber.

 

5. What are the typical angles and alignment tolerances?

 

 Alignment sensitivities are similar to using mirrors.   

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• Total deflection (reflective): 2θ ~8–12°; slant angle ~2° for separation of diffracted and residual reflections.      

• Transmissive AOI: small ~2.5° nominal, total deflection <1°-friendly to straight‑through layouts.

   

 

6. How do these filters pair with SureBlock™ Notch Filters?

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All three variants are spectrally matched (HWHM <10 cm⁻¹) to SureBlock™ ultra‑narrow notch filters. A common high‑performance Raman stack is:

[Two ASE filters] + [90/10 BS] + [two SureBlock™ notches], achieving maximum Rayleigh suppression with high throughput down to ~10 cm⁻¹ from the laser line.

 

7.  Is this difficult to use?

 

Our integrated systems are prepackaged as a complete compact solution as an alternative.     They contain patented solution to minimize temperature sensitivity to operate in larger varying environmental conditions.

 

8. What about power handling and environmental stability?

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VBG gratings show no degradation under high power illumination and are environmentally stable, with testing reported >12,000 h at 150 °C for the transmissive line. Reflective lines state high‑power compatibility and stability in temperature/humidity as well.

 

9. Are these suitable for single‑mode and multimode lasers?

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Yes. Reflective ASE filters specify large angular acceptance and support single‑ and multimode operation. The transmissive version prefers well‑collimated, small‑diameter beams and has polarization constraints.

 

10. What is the temperature drift?

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Typical ~0.01 nm/°C for the ASE and 90/10 BS filters.