1. What are PowerLocker® VBG gratings?

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PowerLocker® gratings are volume holographic (volume Bragg) gratings formed by creating index modulation within the volume of a proprietary photo-sensitive glass substrate. They act as highly selective wavelength filters or reflectors, providing narrowband spectral feedback for laser diodes. They are stable over wide temperature and power ranges and do not degrade over time thanks to robust holographic recording materials.     

 

2. How do PowerLocker® VBGs stabilize (lock) a laser’s wavelength?

 

PowerLocker® VBGs provide narrow-band, wavelength-selective reflection that forces the laser diode to operate at the recorded Bragg wavelength, effectively “locking” the laser onto a stable emission line by:

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• Providing strong wavelength‑selective feedback in an external cavity

• Reducing thermal drift (typically ~0.01 nm/°C)

• Narrowing spectral linewidths significantly

 

This external feedback mechanism forces the diode to lase at the grating’s designed center wavelength, enabling extremely stable output even under varying temperature, current, and aging conditions.     

 

3. What benefits do VBG-stabilized external‑cavity lasers offer?

 

Using VBGs as feedback elements in external cavities provides:

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• High wavelength stability (typically ~0.01 nm/°C)

• Narrow linewidth output (single frequency or typically <0.1 nm for multimode diodes)

• Reduced thermal dependence

• Higher spectral brightness and improved mode selection

• Compact and low‑cost external cavity configurations compared to Littrow/Littman systems

 

4. How does a PowerLocker® VBG compare to traditional diffraction‑grating cavities?

 

Compared to Littrow or Littman external-cavity lasers, PowerLocker® VBGs offer:

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• Shorter cavity length, resulting in more compact assemblies

• Higher stability, because feedback is wavelength‑selective rather than angular

• Lower alignment sensitivity

• Solid-state reliability, as VBGs are monolithic glass elements with no coating degradation

 

5. What wavelengths are available?

 

Typical PowerLocker® VBG wavelengths include:
405, 633, 658, 780, 785, 794.7, 808, 885/888, 920, 938, 940, 976, 981, 1064 nm, plus telecom O-band/C-band and many custom wavelengths from 350 nm to 3 µm.

 

6. What are typical optical specifications?

 

Depending on model and thickness, typical specifications include:

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• Bandwidth (FWHM): 0.03–0.1 nm

• Reflectivity: 5–98% (up to >99% on specialized designs)

• Temperature dependence: ~0.01 nm/°C

• Wavelength tolerance: ±0.5 nm (tighter available)

• Insertion loss: <1%

 

7. Are PowerLocker® gratings suitable for high‑power lasers?

 

Yes. PowerLocker® VBGs are tested under extreme conditions with:

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• No degradation at high optical intensities

• High damage thresholds (e.g., >15 J/cm² for ns pulses at 1064 nm; >170 MW/cm² continuous-wave equivalent)

• Over 12,000 hours of stability testing at 300°C

 

These characteristics make them suitable for multimode diodes, DPSS pumping, and other high‑power applications.

 

8. How are VBGs integrated into an external‑feedback configuration?

 

A typical external-cavity setup involves:

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1. Collimating a semiconductor Fabry Perot laser diode

2. Matching the diode’s free‑running wavelength to within ~1–2 nm of the grating center to ensure strong mode competition favoring the Bragg wavelength.

3. Aligning the VBG such that the diffracted light re-enters the Fabry Perot chip.     In this usage scenario, VBG is a wavelength-selective partial reflector (mirror).   

4. A short external cavity distance results in reduced mode hops and improved stability.

 

9. Can VBGs be used for phase‑locking or beam combining?

 

Yes. VBGs can serve as selective reflectors or transmissive filters in external-cavity phase‑locking of diode arrays. Their angular and spectral filtering functions help enforce coherent operation across multiple emitters. 

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10. What applications benefit from VBG-stabilized lasers?

 

Common applications include:

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• Raman spectroscopy

• DPSS/pumped solid‑state lasers

• LiDAR

• Quantum optics

• Gas sensing and metrology

• RGB light sources

• Telecom (O‑band, C‑band)

• Frequency doubling, nonlinear optics

 

11. Are custom VBG designs available?

 

Yes. Customizations include:

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• Center wavelength

• Bandwidth

• Reflectivity level

• Slant angle

• Substrate size/thickness

• AR coatings

 

Custom wavelength ranges from 365 nm to 2 µm are supported.

 

12. How do VBGs improve system reliability in practical use?

 

Because PowerLocker® gratings are solid-state holographic elements with no moving parts or thin-film layers, they:

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• Maintain performance over the years

• Resist humidity, high temperature, and mechanical shock

• Offer consistent unit‑to‑unit manufacturing reproducibility

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13. What is the difference between vacuum and air-referenced wavelengths?

 

Because we tightly control wavelength accuracy and tolerance, it is important to specify the reference medium used for wavelength measurement.

 

Light travels slightly more slowly in air than in vacuum, causing the wavelength in air to be marginally shorter. To avoid ambiguity and ensure consistency, wavelengths in our datasheets are vacuum‑referenced, which is also the convention used by many spectroscopy databases.  As an example, a HeNe laser specified at 632.991 nm in vacuum corresponds to 632.816 nm in air. This difference does not indicate a physical change in the laser, only a difference in how the wavelength is referenced.