Q UANTUM C ASCADE L ASER U SER ’ S M ANUAL Version number 3.
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COPYRIGHT INFORMATION This manual can be copied and distributed under the following conditions: the work must be attributed in the manner specified by the author or licensor, and cannot be altered or transformed. WARRANTY 1. The customer must control the incoming deliveries and inform A LPES L ASERS about incomplete shipments or defective goods within 30 days after delivery.
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Preface This manual is a reference tool for personnel using A LPES L ASERS QCLs and electronic equipment. Its purpose is to provide the customer with sufficient information to carry out normal installation and operational procedures. It is not intended to replace or supersede any local directive. Table 1 gives a summary of the content of each chapter. CAUTION: All personnel must read and understand this manual before attempting to operate A LPES L ASERS QCLs or electronic device.
Typesetting conventions • Table 2 gives a list of the acronyms used in this manual. • A boxed item indicates a hardware setting on an electronic device. $ ! %% ' % # ( ) * + , " - "" $ ( $' * + ( $ # # %% # & %% - ( # .
Contents Preface v 1. Overview 1.1. A LPES L ASERS products . . . . . . . . . 1.1.1. QCL parameters and performance 1.1.2. QCL geometry . . . . . . . . . . . 1.1.3. QCL mounting . . . . . . . . . . . 1.2. QCL housings and packages . . . . . . . 1.2.1. Laboratory Laser Housing (LLH) . 1.2.2. High Heat Load (HHL) Housing . . 1.2.3. TO3 Housing . . . . . . . . . . . . 1.3. Starter kit . . . . . . . . . . . . . . . . . 1.3.1. Temperature Controller (TCU) . . 1.3.2. Laser Diode Driver (LDD) . . . . . 1.3.3.
3.3.3. 3.3.4. 3.3.5. 3.3.6. 3.3.7. 3.3.8. 3.3.9. TO3 . . . . . . . . . LDD . . . . . . . . . CTL cable . . . . . . CTLm cable . . . . . CPL cable . . . . . . CIL cable . . . . . . . Connection procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 34 35 36 37 38 39 4. QCL Operation 4.1.
7.2.2. TCU calibration . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.3. TPG calibration . . . . . . . . . . . . . . . . . . . . . . . . . . 84 93 A. QCL theory and application notes A.1. QCL wavelength range . . . . . . . . . . . . . . . . . . . . . . . . . . A.2. QCL electrical response . . . . . . . . . . . . . . . . . . . . . . . . . 97 97 98 B. Operations for advanced users B.1. Direct QCL voltage . . . . . . . . . . . . . . . . . B.2. Soldering wire bonds from laser chip to submount B.3.
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1. Overview In this chapter, a general overview of A LPES L ASERS lasers and equipment is given, as well as a brief introduction to the detection principle and fields of application of quantum cascade lasers (QCLs). Contents 1.1. A LPES L ASERS products . . . . . . . . . . . . . . . . . . . . 2 1.1.1. QCL parameters and performance . . . . . . . . . . . . . . . 2 1.1.2. QCL geometry . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1.3. QCL mounting . . . . . . . . . . . . . . . . . . . . . . .
Chapter 1: Overview 1.1. A LPES L ASERS products A LPES L ASERS manufactures Quantum Cascade Lasers (QCLs) of two types: singlemode Distributed-Feedback (DFB) or multimode Fabry-Perot (FP), which can be operated in two modes: continuous wave (CW) or pulsed. A LPES L ASERS lasers are available in different types of packaging, presented in section 1.2. A LPES L ASERS developed dedicated electronics to control the temperature and current drive of its QCLs; see section 1.3 for details.
1.1 A LPES L ASERS products shown in figure 1.2. The ceramic pads surface is covered with a gold layer, and their sides have a whitish ceramic color; the golden surface must be positioned upwards. When looking into the LLH from the top, the pad left of the direction of emission is called DN for down, and the right pad UP for up. Only one pad is characterized, as specified in the datasheet. If only one pad is present, it is in the DN position by default.
Chapter 1: Overview 1.2. QCL housings and packages A LPES L ASERS QCLs can be delivered in 5 kinds of packages: Chip-on-Carrier (CoC) A laser chip available on stock is mounted on either a NS or ST submount (see section 1.1.3) . These submounts can be integrated into a LLH or HHL housing, or can be sold as an such, to be integrated in a piece of equipment manufactured by the customer.
1.2 QCL housings and packages 1.2.1. Laboratory Laser Housing (LLH) The LLH consists in a housing including a TEC and encapsulating the QCL chip; it is designed to ease its installation and replacement. Its internal temperature is controlled by a Peltier junction and a PT-100 or NTC temperature sensor, and can go down to less than -30◦ C. Heat should be dissipated using one of the setups described in section 3.1.2. The LLH temperature is controlled by the TCU (see section 1.3.1). Figure 1.3.: LLH housing.
Chapter 1: Overview 1.2.2. High Heat Load (HHL) Housing The HHL housing is much smaller than the LLH and is completely sealed. The HHL contains a Peltier junction and a PT-100 or NTC temperature sensor, which can be controlled by the TCU (see section 1.3.1) or a local temperature control system. Heat dissipation is performed by thermal contact with its copper base; the heat dissipation capacity depends on the operation mode and environmental conditions.
1.2 QCL housings and packages 1.2.3. TO3 Housing The TO3 housing is a hermetically sealed small-footprint housing designed for integration into commercial devices. It is available in two versions: the TO3-W has a divergent output through an AR coated window, and the TO3-L (shown in figure 1.6) has a collimated output. The TO3 contains a TEC and a NTC temperature sensor.
Chapter 1: Overview 1.3. Starter kit The purpose of the Starter Kit is to readily operate an A LPES L ASERS QCL. The user must provide an external power supply; see section 3.1 for prerequisites and section 1.4 for recommended peripherals. The kit is delivered with all cables needed to connect the LLH or HHL housing, electronic devices (TCU, LDD and TPG for pulsed operation), power cables and connections for optional water cooling.
1.3 Starter kit Pulsed mode The Starter Kit shown in figure 1.8 is meant to operate QCLs in pulsed mode. It consists of the following elements, which are described in dedicated subsections: • Temperature Controller Unit (TCU), section 1.3.1 • Laser Diode Driver (LDD), section 1.3.2 • TTL pulse generator (TPG), section 1.3.3 • CPL and CTL or CTLm cables for laser driver and TCU, section 3.3 2 3 1 4 Figure 1.8.: Starter Kit TCU (2), LDD (3) and TPG (4) for operation in pulsed mode.
Chapter 1: Overview 1.3.1. Temperature Controller (TCU) The TCU purpose is to control the laser temperature inside the LLH or HHL housing. It powers the Peltier junction and reads the temperature from the PT100 sensor coupled to the laser chip (see section 1.2.1). The TCU internal parameters are set in factory according to its use with a LLH or HHL housing. It maintains a preset temperature using the front panel knobs (internal mode) or from a user supplied voltage (external mode).
1.3 Starter kit 1.3.2. Laser Diode Driver (LDD) The Laser Diode Driver shown in figure 1.10 is a switching unit which creates current pulses to drive the laser. The LDD is controlled by a TPG (see section 1.3.3) and powered by an external power supply. It is equipped with a Bias-T for electrical wavelength tuning (see section B.3 for details). Figure 1.10.: Laser Diode Driver (LDD).
Chapter 1: Overview 1.3.3. TTL Pulse Generator (TPG) The TPG shown in figure 1.11 is designed to power and control the LDD (see section 1.3.2) by generating TTL pulses on 50Ω. The pulse duration can be set from 0 to 200 ns and the interval between pulses from 200 ns to 105 µs. See section 5.2 for operation instructions. Figure 1.11.: TTL Pulse Generator (TPG). 12 QCL user’s manual v3.
1.4 Peripherals 1.4. Peripherals The following devices are recommended as peripherals for operating A LPES L ASERS lasers. CW laser driver : precision laser diode current source such as • ILX L IGHTWAVE LDX-3232 High Compliance Quantum Cascade Laser Diode Driver (http://www.ilxlightwave.com/propgs/laser-diode-driver-3232.html) Note: cables compatible with the LLH or HHL housing can be provided by A LPES L ASERS.
Chapter 1: Overview 1.5. Fields of applications 1.5.1. IR The A LPES L ASERS QCLs address the need for gas sensing and spectroscopy applications in the wavelength region from 3 to 15µm as most chemical compounds have their fundamental vibrational modes in the mid-infrared. More specifically, the high transparency of the atmosphere in two so-called atmospheric windows at approximately 3-5µm and 8-12µm allows remote sensing and detection.
1.5 Fields of applications 1.5.2. THz Terahertz radiation is safe and non-ionizing. It bridges the gap between the midinfrared and microwaves. It can penetrate most non-conductive materials and can be used in a wide range of applications: • Water content mapping • Tissue density mapping • Metals detection • Spectral identification Terahertz QCLs operate in the range from 1 to 6 THz.
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2. Safety A LPES L ASERS electronic equipment operates with high voltage and includes a L ASER that may cause serious injury if not handled properly. The guidelines in this document follow as closely as possible the IEC 60825-1 International Standard for safety of laser products. IMPORTANT: This document provides general safety instructions. Site specific safety regulations on electricity and lasers must be followed if they supersede the recommendations in this manual.
Chapter 2: Safety 2.1. General safety considerations If any of the following conditions exist, or are even suspected, do not use the instrument until safe operation can be verified by trained service personnel: • Visible damage • Severe transport stress • Prolonged storage under adverse conditions • Failure to perform intended measurements or functions If necessary, return the instrument to A LPES L ASERS for service or repair to ensure that safety features are maintained. 18 QCL user’s manual v3.
2.2 Notation 2.2. Notation The use of DANGER, WARNING and CAUTION notation in this manual is conform to the SEMI standard S-13-02981 ; their definition is given below. They may also be used to alert against unsafe practices. DANGER: Indicates an immediate hazardous situation, which, if not avoided, may result in death or serious injury. WARNING: Indicates a potentially hazardous situation, which, if not avoided, may result in death or serious injury.
Chapter 2: Safety 2.2.1. Symbols and labels The danger and warning symbols used in this manual are shown in table 2.1. general danger electrical hazard L ASER radiation hazard safety eyewear mandatory Table 2.1.: Safety symbols most commonly used in the A LPES L ASERS user’s manual. 20 QCL user’s manual v3.
2.3 Health hazard 2.3. Health hazard There are three main sources of hazard associated with the Starter Kit: • L ASER radiation, detailed in section 2.3.1; • electrical, detailed in section 2.3.2; • environmental, detailed in section 2.3.3. 2.3.1. L ASER radiation hazard The eye and skin are the body parts the most likely to be injured. Warnings for tasks that may lead to health hazard when operating a QCL are shown below.
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3. Installation This chapter presents the general workflow between delivery and operation of A LPES L ASERS QCLs and electronic equipment: IMPORTANT: The facility must fulfill all prerequisites listed in section 3.1, all utilities must be duly prepared in a suitable location. The location of A LPES L ASERS QCLs and electronic equipment must comply to the environmental conditions listed in section 3.1.1. Contents 3.1. Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.1.1.
Chapter 3: Installation 3.1. Prerequisites In this section are described the environmental conditions in which A LPES L ASERS QCLs and electronic equipment should be stored and manipulated and prerequisites for its operation. The items listed in table 3.1 must be provided by the customer for A LPES L ASERS QCLs and electronic equipment to be operated. It is highly advisable to have the recommended equipment available.
3.1 Prerequisites Storage All A LPES L ASERS lasers are delivered in a hermetic waterproof storage box, shown in figure 3.1, in which the laser chip is held with pins. This box should always be used when storing the laser out of its housing. The laser chip is soldered to the pads using In soldering, which melts at 120◦ C, therefore the storage temperature should not exceed 80◦ C. Figure 3.1.: A LPES L ASERS QCL storage box. QCLs can be stored at ambient temperature (10 to 30◦ C) in normal atmosphere.
Chapter 3: Installation 3.1.2. Cooling The laser performance is highly dependent on its operating temperature, it is therefore necessary to cool down the laser accordingly.
3.2 Receiving procedure 3.2. Receiving procedure Upon delivery of the Starter Kit, the following procedure must be performed: 1. check that all components are included in the shipment. By default, the QCL is included in its housing1 ; the remainder consists of different sets of components depending on the housing and operation mode of the laser. The default packing lists are given in table 3.2.
Chapter 3: Installation MO N 10 ITOR mV IN /CG MaUTP x: 1 U 5V T /6A 22 0−24 0V UN S W DE IQUE/ EM ITH S PL 25 11 FUSI MENT OY 0V 0−12 BL ER 0V ES AVEC DE 25 0v 2 Zin :1 Mo hm 220−240V US E FU ON SE LY Zo ut: 20 0o hm Ex te 10 rnal 0 m Re V/ f. C 0 1 3 Inte rlo ckin g USE ONLYWITH250V FUSES / EMPLOYER UNIQUEMENT AVEC DES FUSIBLES DE 250v 110−120V O 6 7 I Figure 3.3.: TCU installation: rear panel (left), fuse holder (right). 28 QCL user’s manual v3.
3.3 Connections 3.3. Connections Table 3.2 lists the cables and use of all connections for the Starter Kit including the LLH or HHL housing operated in pulsed or CW mode. Refer to figure 3.4 for cable identification.
Chapter 3: Installation 9 8 1 OFF Po we 2 TP G1 28 −T TL ON r ma x 60 mA +1 0 V2V Pu −− lse −− 0.2 G −− 0.5 to 2 ene −− rato −P 5 toto 10.2 m s eri r 10 .5 od 5 msms −− 0 to −− 20 50 0n oh −− Ga ms s −− te − IN 50 Trig oh ms −D OU ura T tion 50 oh ms − Ou t1 Ou t2 10 7 4 3 hm 0O ito r 20 , Z5 A/V V t 12V 60 Inpu pply Max su rol wer nt Po nt co re Cur Mon conn Pu Out ecte lse on put d to top, + hi Bot Hig tom hV olta ge D LD 0 10 TC Tem U1 pera 51 ture Co ntro ller 5 6 Figure 3.4.
3.3 Connections 3.3.1. LLH The LLH front and rear panels shown in figure 3.5 consist of the following items: • anti-reflective (3.5 to 12 µm) ZnSe coated laser beam window (1) • CTL cable connector (2) for Peltier junction and PT-100 sensor • connector for LBI or CIL cable (3) • cooling water flow fittings (4) for 4 mm flexible cables • monitoring base connector (5) and laser connector (6) for direct voltage measurement on the laser.
Chapter 3: Installation 3.3.2. HHL The HHL housing and CTLm cable shown in figure 3.6 must be connected according to the numbering of the CTLm connector pins (from 1 to 10) and the HHL connector pins description provided in section 3.3.6. Figure 3.6.: HHL housing and CTLm cable. 32 QCL user’s manual v3.
3.3 Connections 3.3.3. TO3 Figure 3.7 shows the TO3 housing connector; the pinout is detailed in table 3.3. TO3L and TO3-W housing have identical pinouts. The polarity of the laser connection is specified on the laser datasheet. Figure 3.7.: TO3 housing connector. Pin nb Purpose 1 2 3 4 5 6 7 8 TEC + Thermistor Thermistor laser bondpad laser substrate Not connected Not connected TEC - Table 3.3.: TO3 housing pinout. Note: A LPES L ASERS does not produce cables for TO3 housings.
Chapter 3: Installation 3.3.4. LDD Figure 3.8 show the LDD connectors. The low-impedance line LBI has a locating pin to avoid false connection on the LLH laser housing and on LDD. The LBI has to be connected with "NEG" up unless specifically told to connect with "POS" up. 2 3 50 m Oh ,Z Mo r ito 20 V A/ ut 12V 60V Inp pply ax r su trol M we Po t con en rr Cu n Ou con Pu n ecte lse o tpu d to n top t + h , Bo iH tt igh om Vo lta ge 0 D LD 10 1 Figure 3.8.
3.3 Connections 3.3.5. CTL cable The TCU controls the temperature of the LLH with a Peltier junction and monitors the temperature with a PT100 through the CTL cable. The Peltier connector shown in figure 3.9 carries 6 pins, described in table 3.4. Pin 1 is circled, and a half-moon engraving runs from pin 1 to pin 6. A fixed current is supplied to pin 3 and 6. The resistance of the PT100 varies as a function of temperature and the temperature measurement is given by the voltage between pin 4 and 5.
Chapter 3: Installation 3.3.6. CTLm cable The CTLm cable connects the HHL on one side, and splits into two connectors on the other side: one for the TCU, the other for the laser driver. The TCU controls the temperature of the HHL with a Peltier junction and monitors the temperature with a PT100 temperature sensor. The TCU side of the CTLm cable is the same as the CTL cable, as described in section 3.3.5.
3.3 Connections 3.3.7. CPL cable The CPL cable shown in figure 3.10 connects the LDD to the TPG and external power supply, using a DE-9 connector on the LDD side, yellow/black banana connectors for Bias-T operation, Lemo 00 for LDD power supply, BNC for LDD timing signal and red/black banana connectors for TPG power supply Figure 3.10.: CPL cable. The LDD side consists of a D-sub-9 connector, composed of 9 pins as shown in figure 3.11 and described in table 3.6. Figure 3.11.
Chapter 3: Installation 3.3.8. CIL cable The CIL cable connects the LLH housing to the ILX LDX-3232 CW laser driver. On the LLH end, the connector consists of two rows of pin slots. All slots of one row are connected together, resulting in two terminals. In order to insure the correct polarity, some slots are filled with solder, which should match broken pins on the LLH connector. The ILX side of the CIL cable consists of a D-sub-9 connector, shown in figure 3.11 and described in table 3.7.
3.3 Connections 3.3.9. Connection procedure The procedure to connect the Starter Kit components depends on the laser housing and operation mode. Refer to figure 3.4 for cable identification. In all cases To prevent any damage to the Starter Kit components, make sure the TPG, TCU and the external power supply are all turned off. CAUTION: Make sure that the connectors polarity is correct: the laser’s ground must be floating for both its anode and cathode.
Chapter 3: Installation Pulsed mode operation 1. connect the CPL cable to the LDD 2. connect the LDD to the TPG: a) using the CPL Lemo 00 +12VDC cable for power supply of the LDD b) using the CPL BNC cable into the Out1 and Out2 output IMPORTANT: The LDD ground must be floating. 3. connect the LDD to the external power supply using the CPL red and black banana cables 4. if no bias-T external circuit is to be used, shortcut the signal (yellow) and ground (black) banana cables by connecting them together.
4. QCL Operation In this chapter, the general operation principle of a QCL is presented, and its main characteristics are illustrated using actual plots included in the datasheet provided with each A LPES L ASERS QCL upon delivery. Contents 4.1. Principle of operation . . . . . . . . . . . . . . . . . . . . . . 42 4.2. A LPES L ASERS datasheet . . . . . . . . . . . . . . . . . . . . 43 4.3. QCL spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.3.1. Temperature and current tuning . .
Chapter 4: QCL Operation 4.1. Principle of operation Quantum Cascade Lasers (QCLs) are unipolar lasers emitting in the mid-infrared from 4 to 20 microns. The laser is a ridge of InGaAs and AlInAs grown on InP providing gain and a Fabry-Pérot cavity in order to build up the laser oscillations.
4.2 A LPES L ASERS datasheet 4.2. A LPES L ASERS datasheet The datasheet provided with each A LPES L ASERS QCL upon delivery contains the data obtained from standardized quality control tests performed at A LPES L ASERS production site. The tests are performed on the QCL installed in a test-bench LLH housing operated at a temperature ranging from -30◦ C up to their maximal operating temperature (up to +50◦ C).
Chapter 4: QCL Operation 4.3. QCL spectra A QCL is characterized by its emission frequency (spectral domain), wavelength or wavenumber (spatial domain); all three are equivalent. The following table gives typical values for A LPES L ASERS QCLs. wavelength (λ) 4 - 20 µm 4000 - 20 000 nm frequency (f ) 15 - 75 THz wavenumber (ν ) 500 - 2500 cm−1 4.3.1.
4.3 QCL spectra Figure 4.1.: Spectra of a DFB laser operated in CW mode (top) and pulsed mode (bottom) with different currents and temperatures.
Chapter 4: QCL Operation Figure 4.2.: Spectra of a FP laser operated in CW mode at fixed temperature and different currents. Figure 4.3.: Spectra of four different broadgain lasers. 46 QCL user’s manual v3.
4.3 QCL spectra 4.3.2. Linewidth of pulsed single-mode DFB QCLs The linewidth of DFB QCLs operated in pulsed mode depends on the pulse length, and is affected by chirping, which occurs because of thermal variations of the laser. • Fine linewidth is obtained with short pulses (25 to 50 ns). A LPES L ASERS QCLs are tested using pulse length of 25 to 50 ns, showing a linewidth < 0.2 cm−1 . • Very fine linewidth (< 0.
Chapter 4: QCL Operation 4.3.4. Bandwidth of multi-mode FP QCLs In the case of FP QCLs, the bandwidth is defined as the wavelength range in which 99% of the power is emitted. It depends on the driving current and is not affected by the operating temperature. A LPES L ASERS QCLs operated in CW mode can withstand any pulse length. 4.4. I-V curve and emitted power Figures 4.4 show the IV curves of DFB and FP lasers operated in CW at different temperatures.
4.4 I-V curve and emitted power Figure 4.4.: IV curves of DFB laser (top) and FP laser (bottom) operated in CW mode at different temperatures.
Chapter 4: QCL Operation 4.4.1. Maximum operating current All QCLs have a maximum operating current above which a Negative Differential Resistance (NDR) appears and may destroy the laser. As an example, figure 4.5 shows the IV curve and emitted power of a DFB QCL operated in pulsed mode: the green squares indicate the maximum current for monomode operation, 4.7 A from -30 to 30◦ C in the present case.
4.4 I-V curve and emitted power 4.4.2. Maximum LDD voltage Figure 4.6 shows the pulse peak current and emitted power as a function of the voltage fed to the LDD. In pulsed mode, the QCL operating current is controlled by the LDD, which is itself controlled by changing its operating voltage. The maximum LDD voltage is indicated by green squares on the emitted power curves; in this particular case, the voltage must not exceed 15 VDC.
Chapter 4: QCL Operation 4.4.3. Other DFB QCL plots The plots displayed in figure 4.7 show the emitted power and LDD voltage as a function of frequency, temperature and operating current. These curves help when setting up the operation parameters of a DFB QCL. Figure 4.7.: Emitted power (top) and LDD voltage (bottom) as a function of frequency for a DFB laser operated in pulsed mode at different temperatures. 52 QCL user’s manual v3.
4.5 Beam Properties 4.5. Beam Properties Divergence Figure 4.8 shows a typical A LPES L ASERS QCL beam profile. Unipolar lasers consist in tightly confined waveguides; for this reason, the beam diffracts strongly at the output facet and has a full divergence angle of about 60 degrees perpendicular to the layer (vertical angle) and 40 degrees parallel to the layers (horizontal angle). A f/1 optics will typically collect about 70% of the emitted output power.
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5. Starter Kit Operation In this chapter are presented the operation instructions for the different components of the Starter Kit and the procedures to be followed for starting up and operating an A LPES L ASERS laser. IMPORTANT: The operating parameters are listed in the datasheet provided with each laser; any operation outside the specified range must be agreed with A LPES L ASERS or may result in the loss of warranty. Contents 5.1. Temperature Controller Unit (TCU) . . . . . . . . . . . . . . 56 5.1.
Chapter 5: Starter Kit Operation 5.1. Temperature Controller Unit (TCU) The TCU front and rear panels are shown in figure 5.1 and described below. 1 9 2 3 MaUTP x: 1 U 5V T /6A TC Re set Tem U1 per 51 atu re Co ntr olle r Re Se al ttin C Rea g lI C Se ttin g+ I Se ttin g− I Inte rna l Zo ut: 20 0o hm Ex ter 10 nal 0 m Re V/ f.
5.1 Temperature Controller Unit (TCU) Command description (1) Set Temperature 5 turns knob: Allows to set the internal temperature reference. (2) LCD 3 digits display: Used to display either the actual sensor or reference temperature/current. (3) Switch to select which temperature or current signals to display. (4) Alarm display LED. (5) Alarm reset switch.
Chapter 5: Starter Kit Operation 5.1.1. TCU startup 1. make sure the laser power supply is disconnected (see section 3.3 for connections) 2. turn on the TCU 3. set the desired temperature: a) select Setting oC using the switch (3) shown in figure 5.1 to display the desired temperature b) turn the knob (5) to set the temperature to the desired value c) select Real oC using the switch (3) to display the actual temperature 4.
5.1 Temperature Controller Unit (TCU) 5.1.3. TCU interlock The built-in TCU interlock is activated when a fault occurs on the TCU controller, e.g. prompt temperature rise. The interlock is by default an NC (Normally Close) relay contact, and may be reset by pressing the reset button (3) shown in figure 5.2. Note: it is also possible to set the Interlock as a NO (Normally Open) contact. Ala rm Re set Ex ter nal 2 Inte rna l 3 Figure 5.2.: TCU interlock.
Chapter 5: Starter Kit Operation 5.2. TTL Pulse Generator (TPG) The front and rear panels of the TPG are shown in figure 1.11; a detailed view of the front panel is shown below in figure 5.3. 1 2 3 4 TP G1 28 −T TL Pu −− ls −− 0.2 e G −− ene +12 0.5 to 2 −− rato 0VV −P 5 toto 1.2 µs er i r 1050.5 µ od OF F Po we r ma x6 0m A ON −− Ga 9 50 te IN Trig −− oh m OU s µs s −− −− 50 oh m s T Ou 8 0 to − t1 −D ura tio 50 oh ms Ou 7 200 ns t2 6 5 Figure 5.3.: TPG front panel.
5.2 TTL Pulse Generator (TPG) 5.2.1. Internal and external modes The TPG can be operated in internal or external mode; the mode is selected with a switch on the rear panel of the TPG, as shown in figure 1.11. The input and output signals are provided or generated through the four BNC connectors shown in figure 5.3: • in internal mode, a periodic signal is generated through the Output BNC connector. The Trig OUT BNC connector provides a 200 ns pulse for monitoring purpose or lock-in operation.
Chapter 5: Starter Kit Operation 73* LQWHUQDO VLJQDO 7ULJ ,Q H[WHUQDO VLJQDO 2XWSXW VLJQDO Figure 5.5.: TPG Trig IN external mode signal. 62 QCL user’s manual v3.
5.2 TTL Pulse Generator (TPG) 5.2.2. Setting the pulse parameters 1. remove the TPG from the Starter Kit and connect it to the mains independently 2. set the TPG mode to internal 3. connect the TPG to a scope using the Output should be displayed BNC cable: a 5V TTL signal 4. set the pulse parameters as specified in the datasheet (see section 4.2): a) set the pulse duration to 50 ns using the 0-200 ns knob (4) b) set the pulse period to 2.5 µs using the period knob (2) and toggle switch (3) 5.
Chapter 5: Starter Kit Operation 5.2.3. Maximum duty cycle The TPG is capable of operating with pulses as long as 200 ns; however for short periods (high duty cycle) the following limitations apply: T=400ns: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t max = 200ns T=300ns: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t max = 200ns T=250ns: . . . . . . . . . . . . . . . . . . .
5.3 General procedures 5.3. General procedures CAUTION: The laser shall only be operated under conditions as specified in the datasheet or by A LPES L ASERS directly: all other operation may result in the destruction of the laser and loss of warranty. 5.3.1. QCL startup In order to insure the laser’s performance and enhance its lifetime, the following steps must be followed thoroughly: 1. make sure all devices are turned off 2. start cooling for LLH or HHL housing (see section 3.
Chapter 5: Starter Kit Operation vi. connect the red/black banana cables vii. switch on the external power supply b) setup the TPG pulse parameters following the guidelines of section 5.2 c) connect the TPG back to the Starter Kit and turn it on CAUTION: Make sure the laser temperature is below specifications before turning on the external power supply. Overheating the laser chip may result in permanent damage. 6.
5.3 General procedures 5.3.2. QCL shutdown 1. reduce the external power supply voltage slowly, do not reach 0 as the polarity might reverse CAUTION: Make sure the polarity of the laser is correct. Permanent damage may occur. 2. if the QCL is operated in pulsed mode: turn off the TPG 3. set the TCU to a temperature close to ambient temperature 4. wait until the temperature setting is reached 5.
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6. Technical specifications The technical specifications of A LPES L ASERS products are given in the following tables: • QCLs in table 6.1 • housings in table 6.2 • electronic equipment in table 6.3 • Broadgain Lasers bandwidth in table 6.4 Some technicals drawings are provided in figures 6.5, 6.6, 6.7 and 6.8. !"#$ ?.@$)$'()/$*)$'(0$*,C* ,#$0.<&,' =,>'
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Chapter 6: Technical specifications Figure 6.4.
6.0 2 1 Figure 6.6.: NS (left) and ST (right) mounting support. 1.5 2.5 front view 2 1.5 19 13 3 3 5 3.5 top view 7 2.2 (values in mm) emission from front facet 2 Figure 6.7.: NS mounting.
Chapter 6: Technical specifications 0.6mm pad front view copper submount 2mm 20mm top view "down" pad laser chip 4mm "up" pad 7mm 4mm emission from front facet 1 Figure 6.8.: ST mounting. 74 QCL user’s manual v3.
7. Maintenance In this chapter the maintenance procedures for the installation of a QCL in the HHL housing and Starter Kit components calibration are presented. IMPORTANT: The maintenance procedures included in this chapter have to be followed carefully by expert users only. Delicate operations may result in permanent damage to the laser if not carried out properly. Contents 7.1. Laser installation in LLH housing . . . . . . . . . . . . . . . . 76 7.1.1. Handling . . . . . . . . . . . . . . . . . . . . .
Chapter 7: Maintenance 7.1. Laser installation in LLH housing In this sections are presented guidelines for manipulating the laser safely and the procedure for exchanging the laser in a LLH housing. 7.1.1. Handling The laser should always lay flat, with its vertical axis upwards, on a flat and stable surfaces, without touching anything around its circumference. When mounted in an appropriate and stable holder, it can be operated in any orientation. CAUTION: Do not position the laser upside down.
7.1 Laser installation in LLH housing CAUTION: Do not touch the bonds nor the laser chip itself, as the QCL may be permanently damaged. CAUTION: Avoid any dust to deposit on the laser chip or any laser submount item. Malfunctioning or permanent damage to the laser may occur. 7.1.2. Contact set The contact set shown in figures 7.2 connects the laser active pad to the low impedance line of the LLH through a copper contact, as shown in figure 7.3. Figure 7.2.
Chapter 7: Maintenance 3(7 FRQWDFW VHW ODVHU FKLS SDG VXEPRXQW FRSSHU SODWH EDVH FRSSHU SODWH 3HOWLHU MXQFWLRQ Figure 7.3.: Schematic side view of the laser submount, contact set and LLH. Figure 7.4.: Inside view of the LLH, without (left) and with (right) contact set. 78 QCL user’s manual v3.
7.1 Laser installation in LLH housing 7.1.3. Procedure This procedure allows the installation of a new laser into the LLH housing. 1. disconnect the LLH and open its cover (2), as shown in figure 7.7 1 2 3 4 Figure 7.5.: Exchanging the laser in the LLH housing. 2. remove the two screws (3) holding the contact set (4) using a 2mm hex key 3. remove the contact set using the central PET1 knob, as show in figure 7.6. Note: this PET screw is used as a knob, do not remove it. 4.
Chapter 7: Maintenance Figure 7.6.: Laser exchange procedure: removing the contact set (left), securing the laser submount (right). CAUTION: Do not drop the screws onto the submount. This may result in permanent damage to the laser. 6. secure the laser submount into the LLH with the two dedicated screws; use tweezers to hold the screw in place while screwing with an allen key 7.
7.1 Laser installation in LLH housing 7.1.4. UP and DN contact exchange Follow procedure 7.1.3, adding those additional steps to step 7: 1. remove the screw (5) located at the back of the contact set, as shown in figure 7.7 2. remove the copper contact (6) 3. replace it with the copper contact supplied by A LPES L ASERS with the new laser 4. tighten back the screw (5) 5 6 Figure 7.7.: Exchanging the laser submount UP and DN contact (right).
Chapter 7: Maintenance 7.2. Calibration procedures In this section the calibration procedures for the TPG and TCU are detailed. In both cases a few preliminary steps must be followed: 1. Switch off the device. 2. remove the TPG or TCU cover (refer to figure 7.8): a) Pull off the light gray plastic pieces of the side of the front and back plates. b) Lift off the light gray plastic shades form the side of the box, which gives access to the screws holding the top and bottom covers.
7.2 Calibration procedures 7.2.1. TCU interlock level setting procedure This procedure allows to set the TCU interlock level. 1. switch off the TCU 2. unplug the power cable 3. remove the cover to access the main board following step 2 of the previous procedure. 4. locate the J9 Interlock connector 5. position the associated jumper according the desired type of interlock: • NC (normally closed): pins (4) and (5) • NO (normally open): pins (3) and (4) 3 4 5 Figure 7.9.
Chapter 7: Maintenance 7.2.2. TCU calibration This procedure must be followed for a general calibration of the TCU command knobs and selectors. Refer to section 5.1 for TCU front panel commands description. IMPORTANT: The TCU is calibrated in factory. This procedure is not a routine procedure and must be performed by experts only. Material needed • Voltmeter HP3458A or equivalent. • Voltage source Keithley SMU237 or equivalent. • Precision resistor 100 Ohm 1% or better.
7.2 Calibration procedures 3. +5V/-5V power supply check. CAUTION: Do not connect the signal IN-34 V DC (connector J1 (3)). This may result in permanent damage to the Peltier junction. a) Check that the input impedance between +5V/-5V and GND have the following values: • TP1 (4) - GND (5): > 2.5 kΩ. • TP2 (6) - GND (5): < 4 kΩ. b) Power on the instrument. c) Check that the +5V/-5V power supply voltage have the following values: • TP1 (4) - GND (5): 4.95 to 5.2 V. • TP2 (6) - GND (5): 4.95 to 5.2 V.
Chapter 7: Maintenance 4. Sensing level and range adjustement (refer to figure 7.11) a) Replace the cable connected to J8 (4) with the 100±1 Ω resistor. Note: the precision (gold band on the resistor) is important. Connect one side of the resistor to pins 1 and 2, the other side to pins 3 and 4. b) Measure the voltage on Zn3/R10 (3): the value should be - V = 1.22 to 1.25V. c) Measure the voltage at the intersection of R19/R35 (5): the value should be V=100mV, adjustable with the P1 (2)) knob.
7.2 Calibration procedures 5. Temperature Reference offset adjustment (refer to figure 7.12) a) Adjust B13 (3) to 0.000 with P3 (4) b) Set the temperature with the Set Temperature knob (Fig.40 (7)) to +5 ◦ C ,→ The temperature reference signal B13 should be ≥4.3V c) Set the temperature with the Set Temperature knob (Fig.40 (7)) to -5 ◦ C ,→ The temperature reference signal B3 should be ≤4.
Chapter 7: Maintenance 6. Oscillator check (refer to figure 7.13): measure the frequency on the pin 7 of U13 (1); the value must be 28KHz + /- 3KHz. 7. Current/Voltage ratio adjustment (refer to figure 7.13) a) Adjust the trimmer P4 (6) in order to read B4 = 0.6V (4). b) Set the selector (5) to mode Setting +I: the LCD screen should display 1.00 A. Note: If it is not the case, adjust it with P2 (2). c) Adjust the trimmer P4 in order to read B4 = 3.0 V: the LCD screen should display 5.00 A.
7.2 Calibration procedures IMPORTANT: For the remainder of this procedure, limit the positive current to 1 A and the negative current to 1.2 A using the 5 turns knob. 8. Temperature limit threshold a) Measure the voltage on pin 2 of U10 (1): the value should be: 0.7V (= 70 ◦ C) (If needed, adjust it with the trimmer P9(2)). b) Power off the instrument. 9. Starting the power section of the instrument. a) Remove the 100 E reference resistor from J8 (4) and plug the output cable J8.
Chapter 7: Maintenance 3 4 1 2 Figure 7.14.: TCU main board (zoom III and IV). 90 QCL user’s manual v3.
7.2 Calibration procedures 10. Current adjustment a) Set the selector (3) to mode Setting ◦ C and adjust the temperature value to 25 ◦ C by means of the Set Temperature 5 tuns potentiometer P8 (2). b) On the external power supply, rise slowly the voltage to 30 V and the current to 1.5 A: the tension should stabilize at 30 V. Note: If the current is too high, stop the test and verify the transistors Q1 to Q4 (1) and their associated resistors. There might be a soldering problem.
Chapter 7: Maintenance 11. Temperature limit testing a) Decrease the temperature limit threshold from 0.7 V to 0.3 V. For more details, see Temperature limit threshold on page 89. b) Increase the temperature reference to 35 ◦ C. ,→ When the threshold is overpassed, the red LED (1) in front panel should light up. c) Wait the real temperature drops 10 ◦ C below the threshold. d) Reset the instrument with the RESET button (2). ,→ The red LED (1) should turn off. e) Reset the temperature limit threshold to 0.
7.2 Calibration procedures 7.2.3. TPG calibration This procedure describes the steps to be followed to calibrate the TPG front panel knobs settings. Refer to figure 5.2 for the TPG commands description. IMPORTANT: The TPG is calibrated in factory. This procedure is not a routine procedure and must be performed by experts only.
Chapter 7: Maintenance 2 3 Figure 7.16.: TPG main board (view I). 94 QCL user’s manual v3.
7.2 Calibration procedures [5] Select the range 5 µs to 105 µs on the period selection knob. Turn the 10 turns adjustment knob to its last position. Adjust the adjustable capacitor max 105 µs adj (4) in order to obtain a 105 µs long period. [6] Turn the 10 turns adjustment knob to its first position. Ajust the pot Period min adj (1) in order to have a period of 5 µs. [7] Repeat steps 5) and 6) in order to obtain 105±1 µs and 5±0,1 µs for the two settings of the Period knob. [8] Choose the range 0.2 µs to 2.
Chapter : Maintenance [12] Connect oscilloscope on the Output connector. Load with a 50Ω . Choose a repetition period of about 5 µs. [13] Turn the boxduration adjustment knob to its last position. Adjust the Max duration capacitor (2) to have an output pulse of 200 ns +/-5 ns. [14] Turn the boxduration adjustment knob to its first position. Adjust the pot Out 0ns adj (1) in order that the output pulse is 0ns.
A. QCL theory and application notes A.1. QCL wavelength range Unlike standard bipolar semiconductor lasers (e.g. 1.55µm telecom devices), for which the emission wavelength is closely related to the band gap energy, the QCL transition consists in the transition of an electron inside sub-bands, from one upper quantum well level to a lower quantum well level.
Chapter A: QCL theory and application notes A.2. QCL electrical response The QCL can be modeled with a combination of one resistor and two capacitors. R1 increases from a higher resistance at low biases to 1-4 Ohms at the operating point. The resistance at low bias varies from 10-20 Ω to 102 kΩ for 10 µm and 4 µm wavelength QCLs respectively. C1 is a 100 pF capacitor (essentially bias independent) between the cathode and the anode coming from the bonding pads.
B. Operations for advanced users In this section, tips for advanced users are provided for specific application. It is not recommended to perform those procedures in normal operation conditions. IMPORTANT: The operation instructions contained in this section must be performed by expert users only, as permanent damage to the laser may occur if not manipulated correctly. B.1. Direct QCL voltage These connections give direct access to the voltage of the laser.
Chapter B: Operations for advanced users B.2. Soldering wire bonds from laser chip to submount IMPORTANT: Soldering bonds to the carrier is a delicate operation. Contact A LPES L ASERS before attempting this operation. As the QCL chip itself is soldered, and the contact pads on the ceramics are made out of gold, it is not possible to use a normal Lead-Tin solder: the temperature is too high, the solder will destroy the gold contacts by forming an alloy.
B.3 Bias-T circuit for pulsed lasers B.3. Bias-T circuit for pulsed lasers Since tuning of a QC laser is done by changing the temperature of the active zone, the DC bias current can be used to control the emission wavelength of the laser via its heating effect. The bias-T therefore allows for electrically controlled rapid scanning of the emission wavelength. B.3.1.
Chapter B: Operations for advanced users with increased bias current, due to the additional heating. This reduces the number of lasers available for reaching a given emission wavelength. CAUTION: Applying a high bias current may destroy the laser due to thermal roll-over. Bias-T setup must be performed by instructed personnel and approved by A LPES L ASERS. • The optical output power must be monitored when setting up the bias-T to make sure the thermal roll-over is not reached.
B.3 Bias-T circuit for pulsed lasers Procedure 1. set the temperature to 15o C so that any moisture inside the package does not condense on the laser chip 2. Use current settings as indicated in the A LPES L ASERS datasheet 3. start the laser: the powermeter (if installed) should indicate some power dissipation 4. set the temperature to allow the highest frequency (shortest wavelength) of interest to be emitted 5.
Chapter B: Operations for advanced users B.4. CW modulation To operate a laser in CW mode, an AC signal is added to the DC current. It is recommended to modulate the external power supply directly, within the parameter range specified in the A LPES L ASERS datasheet. If this is not possible, an additional modulated source must be used, like a waveform (ramp) generator for example.
B.4 CW modulation UAC ~ IAC RAC + C IDC UQ L UDC QCL RQ (~ 1-2 Ohm) Figure B.3.: RLC circuit for external power supply protection. In general, XQ is of the order of 1..2 Ω. For a modulation frequency of 10kHz, L should therefore be of the order of 3mH or larger. rules of thumb for R and C To prevent the AC source from dominating or reverse biasing the current through the QCL, UAC < UQ must always be given (in absolute values).
