Pockels Cells

QUBIG offers Pockels Cells with KD*P, RTP, LT, GaAs and BBO crystals for Q-switching of laser cavities, cavity dumping of mode-locked lasers, injection and extraction of laser pulses into and from regenerative amplifiers and beam chopping applications.

In addition to that we provide in combination with our High-Voltage pulse generates and linear amplifiers systems that meet the high requirements for new quantum technology applications including ultra-cold atoms and single photon multiplexing.

General product overview

UV 200 - 400nm	VIS 400 - 700nm	NIR 630 - 1100nm	SWIR 1.0 - 3.0μm	MWIR 3.1 - 4.5μm	LWIR 7.5 - 12μm
PC - UV See details	PC - VIS See details	PC - NIR See details	PC - SWIR See details	PC - MWIR See details	PC - LWIR See details	PC HV short pulses / unshielded
PCA - UV See details	PCA - VIS See details	PCA - NIR See details	PCA - SWIR See details	PCA - MWIR See details	PCA - LWIR See details	PCA analog operation / shielded

Background Information

**Fig. 1** | *Fast switching between s- and p-polarised light by means of a Pockels Cell.*

**Fig. 2** | *Typical frequency response (as Bode plot) of a DC coupled polarisation shifter.*

**Fig. 3** | *a) Effect of a Pockels Cell on the polarisation illustrated by the Poincarè sphere. b) Temporal intensity pattern after an analyser. c) Typical setup*

Altered Light Property: Polarization

The two orthogonal linear polarisation states that are most important for reflection and transmission are referred to as p- and s-polarisation. P (derived from the German word parallel) and S (from the German word senkrecht) are linear polarisations defined by their relative orientation of the electric field (either parallel or perpendicular) to the plane of incidence.

Coupling: DC / Broadband

The electro-optic crystal is directly coupled to the RF modulation input connector, allowing the full bandwidth of the crystal to be utilised. The bandwidth of the Pockels Cell is limited by the output impedance of the driver that forms with the capacitance of the crystal a low-pass filter. For typical retarders with 50Ohms coupling (via e.g. SMA) the limit is about 150MHz. Applications with nano-second response times require much higher bandwidths. In such cases the high voltage is coupled directly to the crystal via short, flying leads in order to keep the capacitance low.

Effect on the Laser Light: Polarization Shift

Pockels cells are voltage-controlled wave plates. The basis of the operation is the Pockels effect which describes the change or generation of birefringence in an optical medium induced by a linear electric field. Pockels cells are commonly used in science and industry to rotate the polarisation of a beam that passes through.

The electric field can be applied to the crystal medium either in longitudinal or transverse configuration with respect to the light beam. Typical longitudinal Pockels cells possess no natural birefringence and thus achieve high extinction ratios. Their halfwave voltage is high but independent (in first order) of the crystal geometry which is useful for high power applications. Transverse arrangements allow geometry dependent halfwave voltage adjustments but suffer from imperfect natural birefringence compensations which limits the extinction ratio and temperature stability.

Alignment of the crystal axis with respect to the ray axis is critical. Misalignment leads to unwanted birefringence which reduces the extinction ratio.

Typical Applications

QUBIG provides Pockels Cells with large clear apertures, very low optical insertion loss, high optical quality and damage thresholds that enable a wide range of applications such as:

**Fig. 1** | *Typical setups for Pockels Cells used as a) Pulse Picker or b) Q-Switch.*

**Fig. 2** | *Basic LiDAR arrangement for Time Of Flight (TOF) detection.*

**Fig. 3** | *Simplified illustration of a Bell-Bloom magnetometer.*

**Fig. 4** | *Illustration of single atoms in an optical lattice manipulated via polarisation and amplitude modulations.*

Pulse Picking & Q-Switching

In industry and science Pockels Cells are used as fast and precise electrically controlled optical switches. Main applications are a) Pulse Picking for extracting single pulses from a pulse train and b) o ptical laser pulse generation either via optical chopping of cw light or by rapid Q-Switching.

LiDAR

In contrast to the "phase shift" method, in which continuous beams of different wavelengths are emitted and the distances are calculated from the phase offset between the transmitted and received signals, the “Time Of Flight” method is based on sending short, staggered light pulses. The transit time of the portion of the emitted radiation reflected by an object serves as an indication of the distance. LiDAR is the analogy to Radar, using laser instead of radio wave. Pockels Cells from QUBIG are useful tools to generate fast laser intensity modulations.

Magnetometry

The atomic magnetometer detects an external magnetic field by exciting atomic magnetic dipole transitions via modulated light (Bell–Bloom magnetometer) and measuring the coherent precession frequency of atomic spins about the external magnetic field. Besides SQUIDs, atomic magnetometer are the most sensitive magnetometers which are used in many significant fields, such as medicine, tests of fundamental symmetries, space exploration, and detection of nuclear magnetic resonance signals.

Research / Science

Electro-optic polarisation shifters find versatile use in many areas of science and research. Besides the use as optical switch for active (de-)multiplexing of single photons, which is a promising candidate for large-scale quantum networks, very often they are implemented for active intensity control of optical dipole traps and lattices. The latter can be used to confine neutral atoms which serve as basis of many exciting topics in fundamental research. Potential applications can be found in ultrafast spectroscopy, high-speed communications and even optical quantum science and technology.