LaseLock®

Universelle Elektronik für die Laser-Frequenz-Stabilisierung

Das LaseLock ist eine universelle und kompakte Laser-Frequenz-Stabilisierungselektronik („Lock-Box“), mit deren Hilfe Laser (wie z.B. Diodenlaser, Ti:Saphir- oder Farbstofflaser) frequenzstabilisiert werden können.

Stabilisierte Laser sind gefragte Komponenten für viele Anwendungen. Durch den Einsatz von LaseLock kann Laserdrift fast vollständig eliminiert und sehr schmale Linenbreiten äußerst stabil erzeugt werden. LaseLock misst und erkennt Frequenzänderungen des Lasers und liefert entsprechende Feedback-Signale, damit diese Änderungen korrigiert und stabilisiert werden können.

Als Frequenz-Referenzen dienen hierbei insbesondere optische Resonatoren oder atomare Absorptions- bzw. Fluoreszenzlinien. Diese Referenzkomponenten sind auch bei TEM Messtechnik erhältlich:

  • CoSy → bietet Referenzstandards basierend auf der Sättigungspektroskopie, wobei Cäsium-, Rubidium- oder Kalium-Zellen erhältlich sind
  • iScan → ist ein aktives Fabry Perot Interferometer, das bei jeder Frequenz ein Stabilisierungssignal liefern kann („active frequency correction“)

Umgekehrt besteht die Möglichkeit, optische Resonatoren mit Hilfe von mechanischen Aktuatoren auf eine vorgegebene Laserfrequenz zu regeln. Die dafür benötigen Treiber stehen als Optionen für LaseLock zur Verfügung (HV-Treiber für Piezo-Aktuatoren, HC-Treiber für Galvos oder DLD-Treiber für Diodenlaser, inkl. – Temp.- und Strom-Regelung).

Key Features

  • Kompakte, eigenständige Lock-in-Elektronik für Diodenlaser, Farbstofflaser, Ti:Sa-Laser oder optische Resonatoren
  • Eingebauter Dither-Generator
  • Side-of-fringe- und Top-of-fringe-Stabilisierung
  • 2 unabhängige PID-Regler
  • Erkennung der Gültigkeit des Lock-in-Punktes und automatische „Such“-Funktion
  • Eingebaute Oszilloskop-Funktionalität
  • Benutzeroberfläche mit Touchscreen und farbiger Signalanzeige
TFT Screen Laser Stabilization LaseLock - Scan function
TFT Screen Laser Stabilization LaseLock - Scan function

LaseLock® scans the laser frequency. Users can search the absorption lines and select the desired line peak for regulation using two threshold values (red and blue line).

TFT Screen Laser Stabilization LaseLock - dither generator
TFT Screen Laser Stabilization LaseLock - dither generator

The built-in dither generator modulates the output voltage. The demodulated input signal is used for regulation. The yellow line defines the set point level.

TFT Screen Laser Stabilization LaseLock - lock-mode
TFT Screen Laser Stabilization LaseLock - lock-mode

In „lock-mode“, LaseLock stabilizes the frequency to a desired absorption peak. Input signal and user-defined thresholds are constantly compared  – the controller searchs and relocks automatically as soon as the signal exceeds the thresholds.

Anwendungsbeispiel

Stabilisierung der Frequenz eines Diodenlasers mit externem Resonator auf eine atomare Absorptionslinie

Bei dieser Anwendung wird die Frequenz eines durchstimmbaren Lasers mit Hilfe einer Referenzzelle stabilisiert. Als Laser kommen z.B. tunbare Diodenlaser, Ti:Sa- oder Farbstofflaser in Frage.

Ziel ist es, die Laserfrequenz auf einen Wert einzustellen, bei dem die Probe eine maximale Absorption aufweist (oder auch minimale Absorption).

This application requires the following components:

  • 1x digital LaseLock with HV option
  • 1x laser with tuneable frequency, here via piezo-actuator (e.g. TOPTICA DL100 diode laser)
  • 1x spectroscopic absorption cell*
  • 1x beam splitter
  • 2x photo detectors

*  We recommend to use the compact spectroscopy module CoSy→, which includes a complete setup for Doppler-free saturation absorption spectroscopy.

Principle of Operation

Two different methods can be applied:

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

Side-of-fringe stabilization is used when a direct discriminator signal can be derived from the measurement signal. In other words, the slope of the peak signal is used to convert frequency fluctuations of the laser into amplitude fluctuations, which can be detected and subsequentely stabilized.

Flankenstabilisierung (side-of-fringe stabilization)

Flankenstabilisierung (side-of-fringe stabilization)

Top-of-fringe stabilization uses a modulation technique and phase-synchronous detection.

For this, the laser frequency (or a different physical measure like the resonator length) is modulated, a detector signal is multiplied with the modulation signal, and then the product signal is averaged by a low pass filter. The resulting ‚lock-in‘-signal represents the derivative of the signal with respect to the laser frequency (or the respective varied physical measure).

This signal can be used directly for physical examinations, because in most cases it contains less disturbing signal parts (noise, offsets) than the directly measured signal.

The zero-crossing of the derivative represents a maximum (or minimum) of the detected signal structure. For stabilization of a laser or resonator towards such an extremum, the ‚lock-in‘ signal is processed by a regulator, which generates a suitable control signal that is fed back (either directly, or for piezo actuators via a high-voltage amplifier) to the frequency-determining element of the laser (or resonator). In this way the control loop is closed and the laser (or resonator) is locked actively to the maximum (or minimum).

Maximum- (Minimum-) Stabilisierung ("Lock-In"-Technik, top-of-fringe stabilization)

Maximum- (Minimum-) Stabilisierung („Lock-In“-Technik, top-of-fringe stabilization)

Anwenderberichte

Stabilisierung eines optischen Resonators mittels einer Drei-Spiegel-Umkehrabbildung

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 eines OPOs zur Erzeugung von Dauerstrich-Terahertz-Strahlung

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.”

Abstimmbares Heterodyn-Infrarot-Spektrometer

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.”

Präzisionsspektroskopie

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. →

Durchstimmbarer cw-OPO

P. Haag:
Realisierung und elektronische Stabilisierung von diodenlasergepumpten einfach-resonanten kontinuierlich-emittierenden optisch parametrischen Oszillatoren aus periodisch gepoltem Lithiumniobat.
Dissertation, Technische Universität Kaiserslautern, 2009

Injection-locking eines Ti:Sapphire Lasers für die Resonanzionisation

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 (jetzt MPQ Garching) sagt:
Die Aufgabe, mehrere Resonatoren mit dem LaseLock von TEM zu stabilisieren, war nicht einfach, aber lohnenswert. Wir konnten die Systeme zuverlässig und stabiler als jemals zuvor stabilisieren →

Erzeugung frequenzstabiler, kontinuierlicher Terahertzstrahlung

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-Spektroskopie an 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.”

Components of LaseLock

Digital LaseLock® combines all components required for or beneficial to this purpose in a user-friendly compact device.

Input section

  • Two separate fast input channels (2.5 MS/s, 14bit)
  • 6 additional input channels (200 kS/s, 16bit)
  • Generation of input signal difference and/or ratio
  • Optional: External preamplifier with supply and remote control from the lockbox

Lock-in-amplifier section

  • Sine/cosine oscillator with adjustable frequency
  • Modulation output with adjustable amplitude
  • Complex phase-synchronous detection
  • 2f / 3f demodulation, user selectable
  • Adjustable detection phase (0 – 360°) and filter cut-off frequency
  • Synchronisation input (optional)

Scan generator section

  • Triangular-shaped scan signal for system adjustment
  • Scan range equal to the regulator output span
  • Adjustable scan frequency and amplitude

Output section

  • Two high-bandwidth regulator output channels (2.5 MS/s)

Options

  • Up to 8 additional input channels (200 kS/s)
  • Up to 16 additional output channels (200 kS/s)

PID regulator section

  • Two PID regulators for simultaneous control of two laser tuning elements (e.g. grating piezo and laser current in an ECDL)
  • Individually adjustable proportional, integral and differential regulator coefficients
  • Second order low pass filter for resonance suppression in mechanical systems
  • Modulation input, e.g. for set point and/or output modulation

Search logic

  • Discriminator logic for recognition of valid and invalid regulation ranges
  • User-selectable action upon loss of regulator input signal: Automatic search scan / regulator hold / reset

Monitor outputs

  • Analog output of relevant internal signals and levels for display on a scope screen

Drivers (optional)

  • HV AMP: High-voltage amplifier for piezo actuators
  • HC AMP: High-current amplifier for galvo scanners
  • DLD: TEC/current drivers for diode lasers

Suitable sensors (optional)

  • CoSy : Compact saturation spectroscopy module (Rb, Cs, K cells)
  • Fabry-Pérot interferometer with detection after Hänsch-Couillaud (PDR-HC)
  • Fabry-Pérot interferometer with detection after Pound-Drever-Hall (PDH)

Technical Data

LaseLock Specification  
Signal input Impedance1 MOhm
Voltage range +/- 1.0 V (fast inputs)
+/- 10.0 V (slow inputs) (others on request)
Bandwidth300 kHz (higher BW on request)
Sampling Rate 2.5 MSps (fast inputs) / 200 kSps (slow inp.)
Resolution14 bit (fast) / 16 bit (slow)
OutputsVoltage range +/- 10.0 V at 1 kOhm load
Impedance 50 Ohm
Sampling Rate 2.5 MSps
Resolution 14 bit
Lock-In amplifier Modulation frequency 0.1 Hz ... 1 MHz
Phase adjustment 0 ... 360°
Cut-off frequency 25 Hz ... 850 kHz
Twin PID regulator Combinations independent / parallel / series
Over-all delay approx. 2 µs
Scan generator Output frequency 100 mHz ... 20 kHz (triangular or saw
tooth shape, TTL trigger output)
SupplyVoltage range 100...240 V AC, 50...60 Hz (auto detect)
Power consumption Typ. < 10 W, (20 W with HV option,
max. 100 W @ full load)
Housing Dimensions H x W x D 88mm x 260mm x 373mm
ControlResistive touchscreen 4.3" (11 cm), LED backlight
Interface USB (RS232, Ethernet on request
Subject to change without notice

Preise (EU-Länder):

ComponentsExplanationSingle unit price (EUR)*
LaseLockDigital all-in-one lock-in box, desktop version3.995,00
LaseLock 24VDigital all-in-one lock-in box, desktop version, supply voltage 12-24 V DC4.050,00
LaseLock 19" 1x2Digital all-in-one lock-in box, 19”- version, 1x2 channels4.795,00
LaseLock 19" 2x2Digital all-in-one lock-in box, 19”- version, 2x2 channels6.690,00
LaseLock 19" 3x2Digital all-in-one lock-in box, 19”- version, 3x2 channels8.585,00
LaseLock 19" 4x2Digital all-in-one lock-in box, 19”- version, 4x2 channels10.480,00
LaseLock 19" 1x4Digital all-in-one lock-in box, 19”- version, 1x4 channels8.165,00
LaseLock 19" 2x4Digital all-in-one lock-in box, 19”- version, 2x4 channels10.435,00
LaseLock 19" 3x4Digital all-in-one lock-in box, 19”- version 3x4 channels12.505,00
LaseLock 19" 4x4Digital all-in-one lock-in box, 19”- version, 4x4 channels14.860,00
LaseLock DFBLaseLock with DFB laser 780, 795 or 850 nm (others on request)on request
HV ampHigh voltage amp, 2 channels670,00
HV amp 4 channelHigh voltage amp, 4 channels680,00
HC ampHigh current amp, 2 channelson request
DLD-DFBDiode laser driver (current and temp control)1.490,00

8 % Preisaufschlag für nicht europäische Länder zuzüglich Versand und ggf. Importzoll/-Steuern im Bestimmungsland.

coming soon.