Passive Q-Switch Laser Technology

Passive Q-Switch Laser Technology for Advanced Driver Assistance Systems

The advancement of autonomous vehicle technologies, or Advanced Driver Assistance Systems (ADAS) is largely dependent on the ability to reduce or eliminate accidents. Giving the vehicle the ability to “see”, even in poor weather conditions is perhaps the biggest challenge to create safe, accident free autonomous systems.

Many new technologies are required to develop comfortable, safe, and reliable autonomous vehicle technologies. However, the LiDAR sensor is believed to be one of the key enablers to achieving mass production and adoption. Today’s automotive grade LiDAR systems are both size and cost prohibitive for series production. It is estimated that LiDAR systems currently employed in self-driving vehicles are over 25 times the estimated price target for mass use.

In partnership with OEMs and autonomous vehicle technology companies, CoorsTek is advancing state-of-the-art LiDAR technology through the development and manufacturing of more efficient designs. These designs employ “passive Q-switch” lasers that rely on ultramodern, highly engineered polycrystalline technical ceramics.    

Ceramics for LiDAR

Polycrystalline YAG Button

Passive Q-switching Technology Explained

Q-switching applies quantum mechanical principles to transform a continuous input signal into a short high energy pulse. Q-switched lasers have output beams of short pulses with high peak power. These beams have much higher power than lasers operating in constant output mode. Pulses produced by Q-switching also allow for higher accuracy ranging than a typical diode or other low power laser methods.

Q-switching involves modulation of intracavity losses, or the “Q factor” of the laser resonator. This technique maintains high cavity losses until activated. The laser is pumped with a diode or flashlamp source until the Q-switch “bleaches” (becomes clear) and allows stored energy in the cavity to build up quickly to create a short, high peak power pulse.

Intracavity losses can be controlled and switched using one of two methods, active Q-switched lasers, and passive Q-switch lasers.

In passive Q-switching, no electrical or moving components are used to repetitively create highly accurate pulses. Passive Q-switched lasers are controlled by a material that initially exhibits high losses until saturation or laser pumping stimulates the material and causes it to become clear. This creates low losses that initiate the laser pulse. The effects of these saturable absorbers are controlled by the material properties and dopant concentration.

Advantages of Passive Q-Switching

Passive Q-switching exhibits many advantages, such as:

  • Component/system simplification
  • Low weight
  • Ease of alignment
  • Elimination of the external power supply or polarizing optics
  • Improved durability and reliability

The working principle of passive Q-Switch technology involves the combination of highly controlled YAG laser crystals. Acting as a laser medium, doped YAG can be engineered to create a desired wavelength. When joined with a passive saturable absorber crystal, such as Cr:Yag or V:Yag, the Q-switch is formed to produce the desired pulsed output beam. 
The type of Q-switch absorber material is selected depending on the lasing wavelength.

Passive Q-Switch Diagram


Limitations of Monocrystalline Ceramics

Today, the passive Q-switching technique is primarily achieved with the use of doped single crystal or monocrystalline solid-state materials, such as cobalt-doped spinel, to produce nanosecond pulses of high energy and peak power with solid-state bulk lasers.

Single crystal provide significant barriers to mass production Not only are these materials expensive and time consuming to produce, scaling is capital intensive. Additionally, the possibilities for adding dopants are limited and difficult to control.


CoorsTek Polycrystalline YAG Materials

CoorsTek polycrystalline YAG materials offer an alternative to single crystal materials with greater control of material properties, higher production yields, simplified processing, and scalable technology. Learn more about CoorsTek Polycrystalline YAG materials.

Click here to request a copy of technical material property data for CoorsTek Polycrystalline Ceramic YAG materials.