In this application, the frequency of a tunable laser is stabilized with the help of a reference cell. Suitable lasers can be tunable diode lasers, Ti:Sa or dye lasers, for example.

The aim is to set the laser frequency to a value at which the sample has maximum absorption (or minimum absorption).

Two different methods can be applied:

• Side-of-fringe stabilization
• Top-of-fringe stabilization (to maximum or minimum, ‘lock-in’-technique)

Application Reports

Stabilization of an optical cavity with a three-mirror image inverter

A. Kosuge, M. Mori, H. Okada, R. Hajima, K. Nagashima: Stabilization of an optical cavity with a three-mirror image inverter for generation of laser Compton scattered ?-rays. Advanced Solid-State Lasers Congress Technical Digest, OSA 2013 →

“By using a three-mirror image inverter which inverts a phase of the specific polarizing direction, we can obtain an “error signal” to lock a cavity without any transmission element […]. … It can be used successfully to lock the cavity to resonance by means of a digital-based cavity lock system (TEM Messtechnik GmbH).”

Seeding of an OPO for generation of terahertz radiation

D. Molter, M. Theuer, and R. Beigang:
Nanosecond terahertz optical parametric oscillator with a novel quasi phase matching scheme in lithium niobate. →
Optics Express, Vol. 17, Issue 8, pp. 6623-6628 (2009) doi:10.1364/OE.17.006623

“We present an optical parametric oscillator pumped by a single mode Q-switched nanosecond Nd:YVO4 laser for terahertz generation in periodically poled lithium niobate with a new phase matching scheme. This new method leads to an emission of terahertz radiation close to the Cherenkov angle and to a parallel propagation of the pump and signal wave. The emission frequency of this novel source is chosen by the poling period to 1.5 THz. For spectral narrowing the signal wave of the OPO is injection seeded. In the optical spectrum also cascaded processes are observed demonstrating a powerful generation of terahertz waves. The OPO itself is also seeded by a grating stabilized diode laser tunable from 1064 nm to at least 1076 nm. Therefore this seed laser is in principle useful to build OPOs for THz frequencies up to 3 THz when pumped at 1064 nm. For the purpose of cavity length stabilization we apply the Haensch-Couillaud stabilization scheme and a commercially available locking system.”

Tuneable heterodyne infrared spectrometer

G. Sonnabend, M. Sornig, P. Krötz, D. Stupar, R. Schieder:
Ultra high spectral resolution observations of planetary atmospheres using the Cologne tuneable heterodyne infrared spectrometer. →
Journal of Quantitative Spectroscopy & Radiative Transfer 109 (2008) 1016–1029

“High-resolution spectroscopy is a versatile tool to study planetary atmospheres. […] The paper will present a detailed description of the Cologne-based receiver THIS, the only tuneable heterodyne infrared spectrometer for application to astronomy offering access to the 7–17 mm wavelength region at a resolution of up to 3 107 and a bandwidth of 3 GHz.

To optimize the superposition of the signal and the laser and to provide a relative frequency standard a confocal FP ring resonator is used, the so-called diplexer. The diplexer consists of two focusing mirrors (focal length 30 mm) and two highly reflective beam splitters […] The locking process is performed in two steps: first, a stabilized Helium–Neon (HeNe) laser operating at 632 nm […] is fed into the diplexer […] . An error signal is provided by a lock-in amplifier which can then be used to actively control the diplexer resonances via the piezo actuator.

In a second step the transmission of the QCL through the diplexer is monitored via the DC component of the heterodyne detector. A second lock-in/feedback circuit is then used to keep the QCL emission at the maximum of the diplexer transmission curve. Following this procedure the LO can be stabilized in frequency to 1MHz RMS (see Section 2.3). […] The stabilization feedback loop consists of two LaseLock units manufactured by TEM Messtechnik.”

Precision spectroscopy

B Sanguinetti , H O Majeed , M L Jones and B T H Varcoe:
Precision measurements of quantum defects in the nP3/2 Rydberg states of 85Rb. →
J. Phys. B: At. Mol. Opt. Phys. Vol. 42 Nr. 16 pp.165004, 2009 L A M

Johnson, H O Majeed, B Sanguinetti, Th Becker and B T H Varcoe:
Absolute frequency measurements of 85Rb nP7/2 Rydberg states using purely optical detection. →

Tuneable cw-OPO

P. Haag:
Realization and electronical stabilization of diode laser pumped single-frequency continuous-wave optical parametric oscillators based on periodically poled lithium niobate.Doctoral thesis, Technische Universität Kaiserslautern, 2009

Injection-locking of a Ti:Sapphire laser for resonance ionization

Dep. of Quantum Engineering, Nagoya University, Japan and RIKEN Nishina Center, Japan, 2012:
Resonance Ionization Spectroscopy in gas jet using a high repetition rate Ti:Sapphire laser system at SLOWRI PALIS. →

University of Jyväskylä, Finnland, 2013:
Injection-locking of a Ti:Sapphire laser for resonance ionization →

Stabilisierung der Idler-Frequenz eines OPO auf einen Lamb-Dip in Methan →

B. L. Yoder, Steric Effects in the Chemisorption of Vibrationally Excited Methane on Nickel, Springer Theses, DOI: 10.1007/978-3-642-27679-8, Springer-Verlag Berlin Heidelberg 2012

Tobias Lamour, Stanford University (now MPQ Garching) says:
Tobias Lamour, Stanford University says: Taking over the task of locking several cavities with the TEM LaseLock was a difficult but rewarding task. We were able to stabilize systems reliably with unprecedented stability →

Generation of frequency-stabilized cw Terahertz radiation

Francis Hindle, Chun Yang, Arnaud Cuisset, Robin Bocquet, Gael Mouret:
A compact CW-THz spectrometer for applications to gas phase identification and quantification of multiple species →

Rydberg spectroscopy of Rubidium

Precision Laser Spectroscopy of Rubidium with a Frequency Comb. Luke Johnson, PhD thesis, University of Leeds, 2011. Pages 94, 95.

“To study the three-step stabilisation scheme, all three laser steps were stabilised to individual Rb reference cells. The first step laser was stabilised using the polarisation spectroscopy scheme introduced in Section 4.2; this is modulation-free. Active feedback for this laser lock was supplied via the laser cavity piezo and the diode injection current. The second step laser was stabilised using the separate co-propagating setup described in Section 4.3.9; FM was added to the laser via the diode injection current. Feedback for this lock was also supplied via the laser cavity piezo and the diode injection current. The third step was stabilised to a Rydberg signal such as those shown in Figure 5.1 and 5.2. Active feedback for this lock was supplied via the laser cavity piezo only. For all three stabilisation schemes, the error signals were sent through PID controllers and then to the laser drivers for feedback, via universal Laselock units (see Figure 5.4).

[…] With this setup it was possible to stabilise to the Rydberg states […]. In principle all states between these will also be accessible. However, for higher n, the lower SNR of the signals prevented a reliable third step lock. The only limiting factor was the available third step laser power.

The results from this study suggest that the absolute frequencies of Rydberg levels could be measured to an accuracy of <100 kHz using this locking technique. This far surpasses the accuracy of the work in Chapter 4, and would give an accuracy comparable to relative microwave spectroscopy measurements.”

Digital LaseLock® is a compact solution that combines all essential and optional components for laser frequency stabilization in one user-friendly device.

The module DigiPDH extends the modulation / demodulation capabilities of LaseLock into the radio frequency (RF) range.

It is the perfect tool for laser frequency stabilization based on the Pound-Drever-Hall principle.

DigiPDH comprises a digital sinusoid signal generator with adjustable frequency between 3MHz and 120MHz and a corresponding phase-sensitive RF receiver with up to 12MHz intermediate frequency (IF or error signal) bandwidth.

It can be combined with the FastPID module that provides individually adjustable proportional, integral and differential gain stages with only 16ns total delay.

With DigiPDH in a Pound-Drever-Hall setup, the signal generator acts as local oscillator for laser phase or frequency modulation. Its adjustable output power of up to +10dBm at 50 ohms suffices to drive resonant EOMs. It also features a return power measurement that helps to find the resonance frequency by minimizing the reflected power.

The DigiPDH receiver mixes the RF input signal (from a photodiode, e.g.) with the local oscillator, thus providing the error signal as a DC signal or at some user-selected intermediate frequency. The conversion gain is adjustable from 0 to +20dB. The generic IF bandwidth of 12MHz is reduced to 1MHz by default. In order to obtain the full bandwidth, the user can simply remove a socketed capacitor.

DigiPDH is available as single-channel or dual-channel version. In the latter, the two LOs and RF receivers can be used independently or in a combined way, i. e. at the same frequency with fixed phase relation, for example to stabilize two subsequent SHG stages.

The second channel could as well be used to drive an AOM as a chopper in a FM spectroscopy set-up.

TEM Messtechnik offers a variety of customizations for the DigiPDH. For example, the receiving mixers can be extended into I/Q receivers, i. e. providing the error signal (IF signal) as sine and cosine signals. In combination with the reflected power detection, the 2-channel DigiPDH can be transformed into a vector network analyzer.

Introduction

The add-on FastPID is a fast analog PID module that extends the over-all bandwith of the Digital
LaseLock® to 6 MHz. Its parameters are adjusted digitally through the host LaseLock’s front panel
TFT or USB interface.
Digital LaseLock® is a universal digital signal processor for laser stabilization. Its over-all delay of ~2μs
allows for a maximum 250 kHz regulation bandwidth. However, fast actuators like EOMs, benefit
from shorter delay times. These can be accomplished using the FastPID, which comes as a plug-in
module inside the Digital LaseLock® desktop or 19” rack case.

Application example

FastPID is perfectly suitable for a Pound-Drever-Hall (PDH) lock.

Technical data

Input voltage range: +/-2V
Input impedance: 1k ohm (termination resistor can be exchanged by the user)
Input offset adjustment range: -2.5V … 2.5V
Error output range: -3V … 3V
Error output impedance: 50 ohms
Intensity input voltage range: -4V … 4V
Intensity threshold adjustment range: -1.25V … 1.25V
Intensity trigger output level: TTL-HC standard (0 / 5V) with 50 ohms output resistor
Output voltage range: +/-10V (typ.), +/-15V (max.)
Output impedance: 50 ohms
Output current: +/-100mA max.
Over-all bandwidth (-3dB): > 6MHz
Overall delay: < 35ns

Pricing (EU-Countries):

8 % surcharge for non-European countries plus shipment and possible import duties/taxes in the destination country.