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 ~400 nm to >2 µm.

 

6. What are typical optical specifications?

 

Depending on model and thickness, typical specifications include:

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• Bandwidth (FWHM): 0.03–1 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 20ns 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 ~400nm 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.

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14. What specifications must be defined to order a VBG?

 

To fully define a VBG it is necessary to specify the following:

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• Diffraction efficiency and tolerance

• Center wavelength, and tolerance

• Is the wavelength specified in air or vacuum?

• FWHM BW (which dictates filter thickness)

• VBG aperture (height * width)

 

15. At what geometry and angle is a VBG typically used?

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Our VBG’s are typically used in Reflection, with the diffracted beam back-reflected on the same side of the filter as the input beam - the back-reflected spectrally-narrowed diffracted beam is used.  Transmission VBG’s are also available.

 

Reflection VBG’s may be used at Normal Incidence, typically for WL stabilization, or at an angle, typically for filtering applications.

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• At normal incidence to the input beam, to retro-reflect a portion of the input back into the diode cavity to 'seed' the cavity for wavelength locking / stabilization.

• At an angle to the input beam, to diffract a narrow WL range and transmit all other WL’s, including ASE.  An ASE filter can be angle-tuned to match a diode WL.

 

Holographic pattern is recorded at a slant relative to the VBG surface, to ensure that the specular reflection from the AR Coated surface will not interfere with the retro-reflected diffracted beam from the grating.

 

16. Are Attalon VBG’s compliant with environmental and regulatory directives?

 

Attalon VBG’s are fully compliant with latest REACH and RoHS directives, and with other regulations and obligations (including Conflict Minerals sourcing, PFAS limitation, California Prop65, etc.)

 

17. What are some of the factors affecting selection of VBG diffraction efficiency?

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VBG Diffraction Efficiency is specified and tested by Attalon at normal incidence, in a well collimated beam.  However, locking stability is determined by the ACTUAL intensity of the feedback that actually couples back into the cavity, ensuring that this feedback becomes the dominant cavity mode.  Attalon can offer samples at a well-documented range of efficiencies to dial in optimal value.  Therefore, the specified diffraction efficiency depends on several factors including:

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1. Placement of the VBG:  VBG placement in a beam collimated using at least a FAC, or FAC/SAC combination is recommended

2. Facet AR coating: Lower diode facet Reflectivity may require lower diffraction efficiency

3. Beam divergence / quality of collimation: Better beam collimation means more of the incident light on the grating meets the Bragg condition, improving the retro-reflected intensity and coupling efficiency into the cavity.

4. Desired temperature/current locking range:  Higher efficiency will retro-reflect a higher intensity, and will always lock better (pulling all modes in the cavity further, and locking over a wider temperature range) than lower efficiency.

5. Grating thickness/angular selectivity:  A thinner grating will Bragg-match the input beam over a wider range of angles. Depending on the details of the external cavity design, this may result in a higher intensity of retro-reflected light.

 

18. What are VBG storage / handling / cleaning suggestions?

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• Handling: Preferred handling is with plastic or teflon-coated tweezers.  If handling by hand, wear gloves or finger cots.  Filters are AR coated on both optical surfaces - avoid touching or contacting these coated surfaces.

• Cleaning: If necessary, clean filters using optical-grade acetone (99.5% pure) or optical-grade Isopropyl Alcohol (99.9% pure), filtered to 0.2mm.  Drag a clean optical tissue soaked in solvent across surface.

• UV Exposure: VBG filter glass is sensitive to UV light, including sunlight and UV curing sources.  Avoid exposure to sunlight or unfiltered fluorescent sources.  If using a UV epoxy curing source, we recommend avoiding broadband sources (e.g. mercury lamp) with spectral components <350nm.  It is preferable to use a narrow-band LED source that operates above 350nm (e.g. 365nm).

• Operating Temperature: Recommended filter operating temperature is <200°C.  Recommended storage temperature is limited by maximum recommended temperature for the packaging.

• Traceability: Individual filters are not generally marked.  Filters are shipped in containers labeled with the part number and lot code, and Attalon maintains complete traceability on all filters by lot code.

 

19. Are VBG’s usable in extreme environments?

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AR Coated VBG’s have been extensively tested and verified to work across a wide range of storage and operating extremes.  This includes tests at hard vacuum, temperature cycling, damp heat, radiation exposure consistent with space use, and AR Coating adhesion and abrasion.