1. What is a CP stabilized laser diode?

 

A CP stabilized laser diode is a wavelength‑stabilized, collimated semiconductor laser using an internal volume holographic grating (VHG) to lock the emission wavelength and spectral characteristics from threshold to rated output power. The unit is compact 9mm diameter with an integrated collimation optic, enabling direct integration into precision instruments without additional beam‑shaping optics.     

 

2. What are mounting considerations?

 

Avoid mechanical stress inside the package. Internal optical components critical to collimation and stabilization are alignment sensitive. Best practices include:

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• Avoid clamping along the beam axis

• Clamp about the diameter of the 9mm ring

• Alternative to clamp is epoxy which helps with thermal contact

• Ensure uniform thermal contact

• Avoid torque or bending loads on the TO‑can

 

Laser needs to be temperature controlled, ideally with TEC. Adjustment to temperature maybe necessary depending on application and lifetime.    

 

3. 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.

 

4. What are typical applications for CP stabilized laser diodes?

 

CP stabilized laser diodes are designed for instrumentation‑grade applications where wavelength stability and spectral purity are critical:

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• HeNe laser replacement

• Raman spectroscopy

• Interferometry and holography

• Precision metrology

• Bio‑instrumentation and fluorescence

• Particle counting

• Analytical and sensing instrumentation

 

These applications benefit from the diode’s narrow linewidth, low temperature dependence (<0.01 nm/°C), and stable single‑mode output in a compact TO‑can form factor.   

 

5. What noise benefits do CP stabilized diodes provide in single‑frequency applications?

 

For single‑frequency and narrow‑linewidth applications, CP-stabilised laser diodes provide important noise performance advantages compared to free‑running diodes. CP diodes are a solution for integration into applications where low noise and compactness are valued.     

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Reduced Frequency Noise

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• The internal VHG wavelength locking suppresses frequency drift and mode competition across the operating current range

• Short cavity makes stability easier to achieve

• Results in lower frequency noise and improved short‑ and long‑term wavelength stability compared to unlocked diodes

• Single‑frequency CP diodes operate without hopping between longitudinal modes when stabilized.    

 

6. Why are single frequency CP laser diodes sensitive to optical back reflections?

 

In single‑frequency CP-stabilized diodes, optical feedback does not only risk permanent damage, it can also significantly increase noise before failure occurs.

 

Back reflections can:

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• Increase frequency noise and linewidth broadening

• Introduce excess relative intensity noise (RIN)

• Trigger temporary unlocking or mode hops

• Cause latent degradation that worsens noise performance over time

 

Use of optical isolators in applications where back reflections occur is recommended.

 

7. How to avoid back reflections?

 

Latent damage can occur due to back reflections which would shorten lifetime. Best practices

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• During alignment (system or fiber coupling), use ND filters to isolate the back reflections. Once aligned, remove the ND filter.

• If fiber coupling, use angled facets to avoid back reflection. Use AR coated facets.

• Aligning narrow bandpass filters are particularly dangerous. Use ND filters or isolators to protect the diode from back reflection until maximum transmission is found.

• All downstream optics should be slightly angled

• If application requires a focal point in a reflective sample, use of isolator is recommended.

• Care must be taken when sweeping or tuning wavelength‑sensitive optics, as brief unlocking of the stabilized diode can generate strong off‑wavelength reflections.

 

 

8. What is the recommended drive method for these lasers?

 

To ensure ultra-low noise and long-term wavelength stability, we strongly recommend using constant current drivers. While constant power modes exist, constant current provides the most predictable environment for maintaining the laser's precise spectral characteristics.

 

9. How does aging affect laser performance?

 

All laser diodes experience a natural decay in output power over their operational lifetime. To maintain a consistent power level for constant current drivers, gradual adjustments to the drive current are typically required.

 

Furthermore, as a diode ages, its "ideal" operating window shifts. This means that the specific combinations of temperature and current that previously yielded a stabilized wavelength may migrate over time.

 

10. What are "mode hops" and how can I avoid them?

 

A mode hop is an abrupt shift in the laser’s longitudinal mode caused by changes in internal conditions (temperature or current). Because the diode’s stable operating regions naturally shift as the device ages, a setpoint that was perfectly stable at installation may eventually drift toward a mode hop boundary.

 

Do I need to worry about this? The necessity of avoiding mode hops depends entirely on your application's sensitivity:

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• Standard Applications: Many power-based or low-resolution applications will not discern these subtle shifts and require no special intervention.

• Precision Applications: For high-sensitivity tasks, such as monitoring interferometric fringes or high-resolution spectroscopy relying on coherence, mode hops can disrupt measurements.

 

Proactive Management: For the longest reliable performance in sensitive environments, we recommend a system design that can sense performance shifts. Periodically re-calibrating the temperature and current setpoints ensures the laser remains centered within its ideal operating window and safely away from potential mode hop boundaries.

11. Why should I cover the beam path?

 

For ultra-precise applications relying on frequency stability, the laser’s performance is influenced by ambient conditions. Even though the laser is mounted on TEC and temperature controlled, air motion would cause fluctuations leading to higher likelihood of entering a mode hope boundary region or frequency changes. Shielding the laser and the immediate beam path in front of the laser would minimize this effect.

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12. What unique capabilities do the CP diodes offer?

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Because we maintain end-to-end control over the production of our PowerLocker® gratings, we offer a level of customization and consistency that is unique in the industry:

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• Precision Wavelength Sets: We can manufacture custom sets of CP diodes with specific, calibrated wavelength spacings tailored to your multi-channel application.

• High Batch Consistency: For large-scale deployments, we provide high-volume production of CP diodes with exceptionally consistent center wavelengths, ensuring uniform performance across all your systems.

13. What versions of CP diodes are available?

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We offer both Single Transverse Mode and Multi-transverse (Lateral) Mode diodes to suit different beam profile requirements. For customers requiring multi-spatial mode wavelengths above 635nm, we recommend our Raman Butterfly product line, which provides a more integrated, compact solution with built-in TEC.