Laser Physics IILaser Physics II

PH482/582-2E (Mirov)PH482/582 2E (Mirov)

Tunable Solid State LasersTunable Solid State Lasers

L t 2 3Lecture 2-3

Spring 2009C. Davis, “Lasers and Electro-optics”

1

Broadband media overview• Natural definition of bandwidth is Δλ/λ0• Natural definition of bandwidth is Δλ/λ0

2

Alexandrite Lasers

3

4

5

6

7

Ti-Sapphire Lasers

8

9

10

11

Chromium doped LiSAF and LiCAF Lasers

12

13

Room Temperature Middle Infrared lasers based on Transition Metal

(TM: Cr2+, Fe2+, Co2+, Ni2+ doped II-VI (ZnS, ZnSe, ZnTe, CdS, CdSe) ( , , , , )

semiconductor crystals

14

OUTLINEI M ti tiI. Motivation

Why TM2+: II-VI?Why Cr2+ and Fe2+?

II. Overview of Cr and Fe-doped II-VI lasersState-of-the-art Cr: ZnS and ZnSe

Sample preparation

III. New regimes of excitation and lasingMicrochip cw and gain-switched lasingMulti-line or ultrabroadband lasing in spatially dispersive cavitiesLasing via photoionization transitionsMid-IR Cr:Al:ZnSe electroluminescence

IV. Fe2+:ZnSe spectroscopic characterization

V. RT Fe2+:ZnSe gain switched lasing over 3.9-4.8μm spectral range

VI Conclusions and Future Outlook

15

VI. Conclusions and Future Outlook

Why broadband laser media?Ultra-short pulses

– time-resolved measurements chemical reaction control– chemical reaction control

– XUV generation – frequency standards

Ult b d tUltra-broad spectra– optical coherence tomography – spectral slicing

i t it b ti– intracavity absorptionBroadly tunable narrowband sources

– optical coherence tomography– spectroscopy– cavity ring-down measurements– photoacoustic measurements

16

Interest for infrared wavelengthsFor femto-chemistry, molecular time-resolved measurements, molecular spectroscopy, trace gas analysis biomedical applications etc one should directly reach molecular fingerprint 2 20gas analysis, biomedical applications, etc. one should directly reach molecular fingerprint 2-20 μm region.

Mid-IR tunable, cw-fs sources are required

Requirements:Requirements:• Sufficient bandwidth• Low cost, compact, directly diode-pumped low threshold• High brightness, i.e. good spatial coherence (TEM00).

Solutions:• OPO (bulk ZGP, PPLN, orientation-patterned GaAs): almost ideal solutions, but rather

complex and costly• QCL: nice solution for λ > 3.4 µm, not as broadbandµ• Semiconductor InGaAsSb/GaSb lasers: narrow tuning, no fs, gap around 2.7-3 µm• Crystalline vibronic lasers: ultrabroadband up to 45 % λ, cw-fs, room-temperature

A h h iTi:S/Cr:LiSAF Cr:Zn/CdSe Fe:ZnSeCo:MgF2

0.2 0.5 1 2 5 10 20 µm

Athmospheric transmission

17Molecular frequenciesCr:YAG Tm:laser

MOTIVATION for TM:II-VIFor molecular spectroscopy, trace gas analysis, biomedical applications, etc. one p py, g y , pp ,should directly reach molecular fingerprint 2-20 μm region. Mid-IR tunable, cw-fs sources are required.

Crystalline vibronic lasers – viable solutionActive interest in TM doped II-VI compounds is explained by the fact thatthese media are close mid-IR analogues of the titanium-doped sapphire(Ti-S) in terms of spectroscopic and laser characteristics and it is(Ti S) in terms of spectroscopic and laser characteristics and it isanticipated that TM2+ doped chalcogenides will lase in the mid-IR with agreat variety of possible regimes of oscillation, similar to the Ti-S laser.

Significant advantages:Significant advantages:TM2+ doped II-VI materials can be directly pumpable with radiation offiber lasers and/or InGaAsP/InP diodes or diode arrays.In comparison with Ti-S they feature higher maximum permissible dopantconcentration higher cross sections and in result microchip lasingconcentration, higher cross sections and in result microchip lasingarrangements are feasible.Due to effective thermo-diffusion of TM in II-VI, diffusion doping ofstarting material is feasible.Have potential for direct electrical excitation (doped QD or QW lasers)

18

Have potential for direct electrical excitation (doped QD or QW lasers).

Why II-VI are so special for Mid-IR lasing?y p gThe heavy anions of II-VI crystals ensure that the optical phonon cutoff occurs at very low energy, thus maximizing the prospects for radiative decay of mid-IR luminescence in these crystals.

Host Phonon

y y

cut-off

ZnTe 210 cm-1

ZnSe 250 cm-1

ZnS 350 cm-1

YAG 850 cm-1

YLF 560 cm-1

19

Why Cr2+ & Fe2+? Calculated Multiplet Structure for 3d impurities in ZnSe (after A Fazzio, et al., Phys. Rev. B, 30, 3430 (1984)

First excited levels lie at the right energy to generate 2-3 (Cr) & 3.5-5 μm (Fe) mid-IR emission.Th d d d fi tThe ground and and first excited levels have the same spin, and therefore will have a relatively high cross-section of emission.Hi h l i l l h iHigher lying levels have spins that are lower than the ground and first excited levels, greatly mitigating the potential for significant excited state

b ti t th labsorption at the pump or laser transition wavelengths.The orbital characteristics of the ground and first excited levels are different, and will experience a significant Franck-Condon shift between absorption and emission, resulting in broadband “dye-like” absorption and emission h t i ti it bl f

20

characteristics, suitable for a broadly tunable laser.

The top two: Cr:ZnSe and Cr:ZnSThe only two types so far to allow tunable CW (also diode pumped!) operation *)

O

The only two types so far to allow tunable CW (also diode-pumped!) operation *).ZnS ZnSe

Lattice constant 5.4 Å 5.67 Å

Crystal structure mixed polytype cubic

10

15

Tm:Y

ALO

Tm:Y

AG

(10-1

9 cm

2 )Er:fi

ber

InG

aAsP

dio

des

GainCr:ZnSCrystal structure mixed-polytype cubic

Bandgap 3.8 eV 2.8 eV

Hardness (Knoop) 160 120

1400 1600 1800 2000 2200 2400 2600 2800 30000

5 σ Co:MgF2

Absorption

Wavelength, nm

( )

Thermal conductivity

27 W/mK (cubic)

17 W/mK (hex)18 W/mK

dn/dT (10-6 K-1) 46 70

15

Tm:Y

ALO

Tm:Y

AG

m2 )Er

:fibe

rsP

dio

des

GainCr:ZnSe

dn/dT (10 6 K 1) 46 70

Transparency 0.4–14 µm 0.5–20 µm

Refractive index 2.27 2.45

1400 1600 1800 2000 2200 2400 2600 2800 30000

5

10

σ (1

0-19 c

InG

aAs

Co:MgF2

Absorption

Emission peak 2350 nm 2450 nm

Absorption peak 1680 nm 1780 nm

Lifetime (300 K) 5 µs 4 µs

21

1400 1600 1800 2000 2200 2400 2600 2800 3000Wavelength, nm

I.T. Sorokina, E. Sorokin, S. Mirov, V. Fedorov, V. Badikov, V. Panyutin, K. Schaffers, Opt. Lett., 27, 1042 (2002).

Slope efficiency 53 % 71 %

Mid-nineties: Zn-chalcogenide lasers,( Livermore Group L. DeLoach, R. Page et al 1996)Cd-chalcogenide lasers, ( K. Schepler et al (Cr:CdSe), and S. B. Trivedi et al (Cr:CdTe and compounds) 1997)

Best results Cr:ZnSe, Cr:ZnS, Fe:ZnSe

Crystal Laser Characteristic Output parameter ReferenceCr:ZnSe CW, output power, W 13 I. Moskalev, V. Fedorov, S. Mirov, P. Berry, K. Schepler, ASSP’09

CW, Tuning Range, nm 2000‐3100 I.Sorokina, Solid State Mid‐Infrared Laser Sources, vol. 89, 2004.

CW, efficiency, % 60‐70 G.J.Wagner, et al., Opt. Lett., 24, 19‐21 (1999).

CW, microchip, output power, W 3 I. Moskalev, V. Fedorov, S. Mirov, Optics Express 16, 4145 (2008)

CW, Hot‐Pressed Ceramic Laser, W 0.25 I. Moskalev, V. Fedorov, S. Mirov, Optics Express 16, 4145 (2008)

CW, Single Frequency, oscillation linewidth, MHz

20 @ 10 mW<120 @ 150 mW

G.J.Wagner, et al., ASSP 2004, WB12.I.Moskalev, et al., 6552‐36, Laser Source Technology…III

CW, Multiline operation 40 lines over 2.4‐2.6 μm I. Moskalev, S. Mirov, V. Fedorov, Optics Express 12, 4986 (2004).

Pulsed, Output power, W 18.5 @ 10KHz T.J.Carrig, et al., Proceedings of SPIE Vol. 5460, 74‐82 ( 2004).

Pulsed, Output Energy, mJ 14 @ 200μs P.Koranda, et al., Optical Materials, in press (2007)., p gy, 14 @ 200μs Pulsed, Tuning range, nm 1880‐3100 U.Demirbas, A. Sennaroglu, Opt. Lett., 31, 2293‐2295 (2006).

Pulsed Microchip, Energy, mJ 1 S.B.Mirov, et al., CLEO 2002, pp.120‐121.

Gain‐switched, Hot‐Pressed Ceramic Laser, Energy, mJ

2 @ 5 ns A. Gallian, V. Fedorov, S.Mirov, et al., Opt. Expr. 14, 11694 (2006).

Mode‐locked, duration, fs 80 @ 80 mW I.Sorokina, E.Sorokin, ASSP 2007, WA7. “

Cr:ZnS CW, output power, W 10 I.Moskalev, V.Fedorov, S.Mirov, et al., Photonics West 2009.

CW, Tuning Range, nm 1940‐2840 I.Sorokina, E.Sorokin, S.Mirov, et al., Opt. Lett., 27, 1040 (2002).

CW, efficiency 53% S.B.Mirov, et al., Optics Letters, 27, 909‐911, (2002).

CW, microchip, output power, W 0.1 S.B.Mirov, et al., Optics Letters, 27, 909‐911, (2002).

Gain‐switched Microchip, Energy, mJ 0.5 S.B.Mirov, et al., CLEO 2002, pp.120‐121.

M d l k d d ti f 1100 @ 125 W I T Sorokina E Sorokin T J Carrig K I Schaffers ASSP 2006 TuA4 Mode‐locked, duration, fs 1100 @ 125 mW I.T.Sorokina, E.Sorokin, T.J.Carrig, K.I.Schaffers, ASSP 2006,TuA4.

Fe:ZnSe Pulsed @150K, energy, μJ 5 J. J. Adams, et al., Opt. Lett., 24, 1720‐1722 (1999).

Pulsed@85K, energy, mJ 187 A. A. Voronov, et al., ” Quantum Electron., 35(9), 809‐812 (2005).

Pulsed, efficiency,% 43 A. A. Voronov, et al.,” Quantum Electron., 35(9), 809‐812 (2005).

Microchip gain‐sw. @300K, energy, μJ 1 @ 5ns J.Kernal, et al., Optics Express, 13, n 26, 10608‐10615 (2005).

Gain‐switched @300K, energy, mJ 0.4 @60 ns V.A. Akimov, et al., Quantum Electronics 36, 299‐301 (2006).

Gain‐switched @300K, tun. range,nm 3950‐5050 V.V. Fedorov, S.B. Mirov, et al., IEEE J. of QE 42, 907‐917 (2006).

Fabrication methods and problems to be resolvedB id t h iBridgman technique (sublimation of chemicals requires simultaneous use of high temperature and pressure, (1550C & 75 atm. – economically not viable)

Chemical vapor transport (CVT) (doping is very difficult)p p ( ) (Physical vapor transport methods (PVT) (doping is very difficult)

Pulse laser depositionHot-pressed ceramicsThe post-growth thermally diffusion doping by Cr or FeAll these methods have problems requiring additional studiesAll these methods have problems requiring additional studies

Key Challenges:Hard to get High Cr concentration High scattering loss

Low damage thresholdHard to get Uniform Cr distributionHard to make Large Cr2+:ZnSe crystals

Low damage thresholdStrong thermal lensing effects

Our goal was to improve quality of the Cr:ZnSe/S and optimize crystal

23

Our goal was to improve quality of the Cr:ZnSe/S and optimize crystal geometry to obtain multi-watt CW lasing in non-selective, dispersive and microchip modes of operation.

Pulsed Laser Deposition Growth of Thin Films

Target: ZnS/Fe Substrate: Si at 550oC or 650oCTarget-substrate gseparation: 5 ~ 10cmPressure vacuum: 2.6 × 10-6 torrLaser: 248nm KrF, 30 Hz rate, energy density 2J/cm2yPost annealing is applied

24

S. Wang, S. B. Mirov, V. V. Fedorov, R. P. Camata, “Synthesis and spectroscopic properties of Cr doped ZnS crystalline thin films” in Solid State Lasers XIII: Technology and Devices, Proceedings of the International Society of Optical Engineering (SPIE) (2004) Vol. 5332, 13-20 Editors: Richard Scheps, Hanna J. Hoffman (ISBN 0-8194-5240-8)

Surface & cross section SEM (ZnS results)( )

Cross section 2500x Surface 5000x

1.5 hours deposition + 1 hour post annealing, at 550oC substrate temperature

25

S. Wang, S. B. Mirov, V. V. Fedorov, R. P. Camata, “Synthesis and spectroscopic properties of Cr doped ZnS crystalline thin films” in Solid State Lasers XIII: Technology and Devices, Proceedings of the International Society of Optical Engineering (SPIE) (2004) Vol. 5332, 13-20 Editors: Richard Scheps, Hanna J. Hoffman (ISBN 0-8194-5240-8)

Hot-pressed Ceramic PreparationZnSe ZnSe+ P=30-350MPaZnSe

P=60MPa

CrSe(1%) ∅15 mm

2ZnSe+ CrSe(0.1-0.01%)

300

nerg

y (m

J)B

W

200

250

300

iiOC 10

CW regime

Gain-switched regime

Out

put E

n

1 BC

η=3%η=5%

Pout

, mW

50

100

150

i

%

OC 5%

e

Abs. Energy (mJ)0 10 20 30 40 50 60

0

Pabs, W0.5 1.0 1.5

0

50

26A. Gallian, V. V. Fedorov, S. B. Mirov, V. V. Badikov, S. N. Galkin, E. F. Voronkin, and A. I. Lalayants, " Hot-pressed ceramic Cr2+:ZnSe gain-switched laser ," Opt. Express 14, 11694-11701 (2006).

Bulk Crystal Preparation by post-growth thermal diffusionTh l liThermal annealing

Crystal growth or Infrared window purchase

C lCrystal

Cr thin film deposition

P=10-5 torrT= 950-1000 C t=3-10 days

PowderCrystaldeposition

The polished samples of up to 7 mm thickness can be

• Uniformly-doped, reasonably large samples;

• Low scattering loss in thermally diffusion doped crystals; mm thickness can be

prepared doped crystals;

• Strong thermal lensing effects;

Good for High-Power (t bl ) L

27S.B. Mirov, V.V. Fedorov, (November 1, 2005) Mid‐IR microchip laser: ZnS:Cr2+ laser and saturation absorption material”, US Patent No 6,960,486.

(tunable) Lasers

Power‐Scaling of Cr:ZnSe CW LasersNew Technology: High‐Quality Cr2+:ZnSe Crystals

9

Uniformly-doped5x5x20 mm crystal

7

3 1 @ 1 6k~3 cm-1 @ 1.56 μm

5 mm3

Cross-section cut from the middle h if C

Key Properties:• Uniform Cr distribution• Negligible scattering loss• Pre assigned Cr concentration shows uniform Cr

distribution• Pre-assigned Cr concentration• Large, engineered (undoped ends,

gradient concentration) crystals are feasible 28

Power‐Scaling of Cr2+:ZnSe CW Lasers: Cavity ConfigurationCompact Folded 3 mirror Kogelnik Cavity:

Pump Lasers Available:1. 9.5 W Linearly-Polarized

Er-fiber Laser; Up to 7.5 W could be used due to

Compact, Folded, 3-mirror Kogelnik Cavity:Easy to align;Brewster astigmatism compensation;Good output beam quality obtainable; Convenient mode size control;

R1

could be used due to losses on delivering optics;

2. 30 W Randomly-Polarized Er fiber Laser; Up to 13 W

Convenient mode-size control;Crystal geometry:Thin 2.5x7x9mm slab placed between twoair-cooled Cu heat sinks

R1R2 d1

d2

1.56 μm Pump

Beam

Cr2+ZnSe Er-fiber Laser; Up to 13 W could be used due to Fresnel loss on the Brewster surface of the laser crystal;

d3

Pump lens laser crystal;

Previously reported state-of-the-art:1 4 W CW 4 2 @ 10kHz thin-disk

Cavity parameters: Pump lens: f=75 mm; R1=50 mm;

1.4 W, CW, 4.2 @ 10kHz thin disk laser by Schepler et al (2005)1.8 W, CW Kogelnik cavity by Wagner et al (2001)18 5 QCW (duty cycle10-3) Carrigy p p ; 1 ;

R2=50 mm; d1=55 mm; d2=26 mm; d3=100 mm;

29

18.5 QCW (duty cycle10 ) Carrig et al (2004)

I.S. Moskalev, V. V. Fedorov, and S. B. Mirov, Optics Express 16(6), 4145-4153 (2008).

High-Power Cr2+:ZnSe Polycrystalline CW Laser: New Technology Crystalsgy y

I.S. Moskalev, V. V. Fedorov, and S. B. Mirov, Optics Express 16(6), 4145-4153 (2008).

Pumped by randomly-polarized Er-fiber laser 30

State of the art in Cr:ZnS and ZnSe microchipsZnS:Cr2+ (d=1 mm) or

ut,W 0 .4

0.5

0.6

Output coupler3.5% transmission over 2300-2500 nm

Er fiber or diode

laser

ZnSe:Cr2+ (d=2.5 mm) CrystalInput mirror Cr:ZnSe microchip

Pou

0 .1

0.2

0.3

Ge Filter

1.55-1.9 μm

2280-2360 μm (ZnS) 2480-2590μm (ZnSe)

Pabs,W0 1 2 3 4

0.0

Coupling optics

y, a

rb.u

n.

Cr2+:ZnS

y, a

rb. u

n.

Cr2+:ZnSeA

A

arb.

un.

0.6

0.8

1.0

Inte

nsity

2300 2350

Inte

nsity

B B

2400 2600

C

-10 -8 -6 -4 -2 0 2 4 6 8 10 12 14

Inte

nsity

, a

0.0

0.2

0.4

31

nm2550 2600nm2300 2350mm

10 8 6 4 2 0 2 4 6 8 10 12 14

High-Power Cr2+:ZnSe Polycrystalline Microchip CW Laser

2θ ~ 1.3 mrad

I.S. Moskalev, V. V. Fedorov, and S. B. Mirov, Optics Express 16(6), 4145-4153 (2008).

Input mirror Uncoated2

M2~2.2

Input mirror Cr2+:ZnSe 9x7x3 mmAR@1.56 μm HR@2.1-2.8 μm

Positive thermal lens forms a stable resonator within theplane-plane cavity;The output power roll-off occurs due to change in theThe output power roll-off occurs due to change in the thermal lens focal length as the intracavity light intensity is increased; 32

Cr:ZnSe Single-Frequency CW Laser: SetupI.S. Moskalev, V. V. Fedorov, and S. B. Mirov, Optics Express 16(6), 4145-4153 (2008).

Key Features: • Kogelnik – Littman Folded Cavity; • Rapidly tilted tuning mirror: 10--220 Hz;

Key Results:Compact design: 10 cm and smaller; High output power: 150 mW at 5 W pumpWide tuning range: 2440-2560 nm;

I.S. Moskalev, V. V. Fedorov, and S. B. Mirov, Optics Express 16(6), 4145 4153 (2008).

• Fiber-laser pumping: 1.56 μm, 7 W max;• TEC/AIR cooling;

R1R Pump lens

Wide tuning range: 2440 2560 nm;Narrow linewidth: 80-130 MHz;Rapid wavelength tuning: 4.5 μm/s;

R2d1d2

d3 D

1.56 μm Er-fiber laser

Grating 600 g/mm

d3

d4

WavemeterD1 Scanning

FPI

Distances: d1=d2=25 mm, d3=30 mm, d4=20 mm. Mirrors and lenses: R1=25 mm, R2=50 mm, Pump lens f=50 mm. D1 and D2 optical detectors.

D2Tuning mirror Output beam

2 p 1 2 p

33Previously reported state-of-the-art:

20 MHz, 10 mW @ 2460 nm. Grating and 2 FP etalons. Carrig (ASSP’ 2004)

High-power, widely tunable polycrystalline CW Cr2+:ZnSe laser

7x3x9 mm (9 mm is the length) uniformly doped polycrystalline Cr2+:ZnSe crystal7x3x9 mm (9 mm is the length), uniformly-doped polycrystalline Cr2+:ZnSe crystal (absorption coefficient k~4 cm-1 at 1.56 µm pump radiation.X-type Littrow grating cavity, the total cavity length is 30 cm, the whole laser system fits on the 20x25 cm breadboard.The 95% efficient (at 45° incident angle) 600 g/mm Littrow diffraction grating isThe 95% efficient (at 45 incident angle), 600 g/mm Littrow diffraction grating is mounted on a computer controlled rotation stage and the laser wavelength tuning is performed with “one knob” over the entire tuning range of 2.12-2.77 µm.

High-power, widely tunable polycrystalline CW Cr2+:ZnSe laser

Δλ~ 1 nm, ηreal=20%I.S. Moskalev, V. V. Fedorov, and S. B. Mirov, Optics Express 16(6), 4145-4153 (2008).

“Spatially Dispersive” Multiline and ultrabroadband lasersU.S. Patent No. 5,471,493, U.S. Patent No 6,236,666 “Application of laser beam shaping for spectral control of “spatially dispersive” lasers” Chapter

Ix )sin(2 αβλ += tk

Application of laser beam shaping for spectral control of spatially dispersive lasers Chapter 7, pp.241‐267, in Laser Beam Shaping Applications, Dickey, Holswade, Shealy ‐ Eds., Taylor & Francis, ISBN 0‐8247‐5941‐9, 2005.

wm wc wD

Aperture A

λ1

λ2 λ3

Spatial mask λ

x

f≈α

d 224 λλ

)sin(2 αβλ += tk

wD

Active Lens L

Δx

Pump Beam f

tft

dxd 2

024

cos2 λβλ −

==

l d1d0z

wgmediumLens L1

Mirror M1I

⎞⎛

( ) ( )λoscpump IxI →

where( ) ( )xI

LTTI pumpSTabsosc ηηλ ⎟

⎠⎞

⎜⎝⎛

+= 2

02

0 4 λλλ −+≈ tfx

where

Multiline and ultrabroadband lasersU.S. Patent No. 5,471,493, U.S. Patent No 6,236,666 “Application of laser beam shaping for spectral control of “spatially dispersive” lasers” Chapter 7, pp.241‐267, in Laser Beam Shaping Applications, Dickey, Holswade, Shealy ‐ Eds., Taylor & Francis, ISBN 0‐8247‐5941‐9, 2005.

1

LiF CCL Multiline 1& 2ω Multiline diode laser Multiline Cr2+:ZnSe

(b)

units 0.8

1.0luminescencemultiline lasing

110 115 120 125

I, a.

e.

0 Inte

nsity

, rel

ativ

e u

0.2

0.4

0.6

Wavelengh, μm1.10 1.15 1.20 1.25

I Moskalev et al OpticsT B i t l A l O ti I. Moskalev et al. Opt.

Wavelength, nm

1550 1560 1570 1580 15900.0

ve u

nits 0.8

1.0luminescencemultiline lasing

I. Moskalev, et. al. Optics Express 12, 2004

T. Basiev et al., Appl. Optics 36, 2515 1997

I. Moskalev et al. Opt. Comm. 220, 161 2003

Inte

nsity

, rel

ativ

0.2

0.4

0.6

37

640 645 650 655 660 665 670 675 6800.0

Fe2+:ZnSe problemIt was believed that because of the small energy gap thermally activatedIt was believed that because of the small energy gap , thermally activated

multiphonon quenching in Fe:ZnSe mandates cryogenic laser operation.

PL lifetime vs temperature (Adams, OL24, 1720 (1999)

Possible solution – gain switched regime of operation with pump pulse duration shorter than Fe2+ lifetime at 300K

38

pump pulse duration shorter than Fe2 lifetime at 300K

RT Fe:ZnSe Lasing in nonselective and prism CavityIEEE J of Quantum Electronics 42 (9) 907 917

0.500.4

IEEE J. of Quantum Electronics 42 (9), 907‐917, September 2006

Ener

gy, m

J

0 25nerg

y, m

J

0 2

0.3

Out

put E 0.25

Out

put E

n

0.1

0.2

Wavelength, μm

4.0 4.2 4.4 4.6 4.8 5.0 5.20.00

Absorped Energy, mJ

0 1 2 3 4 50.0

g μp gy,

Input-Output characteristics of the gain switched Fe2+:ZnSe laser at RT

Tuning curve of room-temperature Fe2+:ZnSe laser with intra-cavity prism obtained at

39

switched Fe :ZnSe laser at RT. ase t t a ca ty p s obta ed atabsorbed pump energy of 4.5 mJ.

Fe doped CdMnTe crystals – promising gain media for 4000-6500 nm lasingg g

Fe2+ (RT)

n, c

m-1

20

25

30

CO2

A

al V

10-1

B

-tim

e, u

s

10

100

i

vi

Abs

orpt

ion

5

10

15

ZnSeCdMnTe

0 20 40 60

sign

a

10-3

10-2

0 50 100 150 200 250 300

life

0.1

1

i

ii

iiiiv

v

Wavelength(nm)

2000 3000 4000 5000 6000 7000 8000 90000

time, us0 20 40 60

T, K

0 50 100 150 200 250 300

CO absorption

W. Mallory, Jr., V. V. Fedorov, S. B. Mirov, U.

ensi

ty, a

.u

Pump Second Order

CO2 absorption14K

, ,Hömmerich, W. Palosz, and S. B. Trivedi, Proc. of SPIE Vol. 6871, 68712T (2008)In

te

RT

68712T (2008).

wavelength, nm

3500 4000 4500 5000 5500 6000 6500 7000

40

Fe:ZnSe passively Q-Switched Er:Cr:YSGG laserA d G lli Al M ti P t i k M i Vl di i F d S Mi * V l i B dik D M B t d M A d iAndrew Gallian , Alan Martinez , Patrick Marine , Vladimir Fedorov , Sergey Mirov*, Valeri Badikov D. M. Boutoussov, and M. Andriasyan,

“Fe:ZnSe passive q-switching of 2.8-µm Er:Cr:YSGG laser Cavity”, Proceedings SPIE Vol. 6451 (SPIE, Bellingham, WE, 2007)..

1 pulse 6 mJ & 7J pump for 80% R OC

2 8μm 2 941 pulse13 mJ30 J pump40% efficiency

T=90%

2.8μm 2.94μm

yScheme (b)

19 pulses85 mJ30 J pump

5 pulses25 mJThe combination of a high values 30 J pump

40% R OCScheme (a)

25 mJ20 J pump40% R OCScheme (a)

of saturation cross-section (0.9x10-18 cm2, small saturation energy with good opto-mechanical (damage threshold - 2J/cm2) and physical characteristics of ZnSe

41

physical characteristics of ZnSe and ZnS hosts make Fe2+:ZnSe/S crystals an ideal materials for passive Q-switching of mid-infrared laser cavities.

Single frequency Cr:ZnSe passively Q-Switched Er:YAGQ Switched Er:YAG

Bragg 1.0%, 30 mm Er:YAG 370 mm

I. Moskalev, et al., Optics Express, 2008 in preparation

f=400 mm34 mm2 mm

10 mmgrating

f=75 mm

45 mm

Cr2+:ZnSe Q-switch

Cr2+:ZnSe

18cm

2 1.0 1.645μm

35 mmswitch

Flat 100% end

σx10

-

0.0

0.5

Flat 100% end mirror

Schematic diagram of the optical scheme of the passively Q-switched Er:YAG laser.

Wavelength, nm1000 1500 2000 2500

0.0

42

Single frequency Cr:ZnSe passively Q-Switched Er:YAGE YAG P i l Q it h d l t t PEr:YAG Passively Q-switched laser output Power vs pump

, W 4

5 CW, ηreal~30%, ηslope~42% Q-switched, ηreal~14%, ηslope~20%

7 kHz Passively Q-switched Er:YAG laser SLM pulse

0.8

1.0τFWHM ~ 65 ns

e O

utpu

t Pow

er

2

3

4

Sign

al, a

.u.

0.4

0.6

Ave

rage

1

2

Time, ns0 50 100 150 200 250 300 350 400

0.0

0.2

Pump power, W2 4 6 8 10 12 14 16

0SLM Passively Q-switched Er:YAG laser pulse train

0.8

1.0

Sig

nal,

a.u.

0.4

0.6

Cr2+:ZnSe and Cr2+:ZnS saturable absorbers are ideal materials for passive Q-switches of eye-safe fiber and solid-state lasers operating in the spectral range of 1.5-2.1 μm.

43

Time, s0.000 0.001 0.002 0.003

0.0

0.2 I. Moskalev, et al., Optics Express, 2008 in preparation

Future electrically pumped Cr and Fe doped Quantum Dot and Quantum well broadly tunable mid-IR lasersand Quantum well broadly tunable mid-IR lasers

Cr and Fe doped II-VI lasers combine the versatility of the ion-doped solid-state lasers with the engineering capabilities p g g pof semiconductor lasers, paving the route to the future electrically pumped ultrabroad-band solid-state lasers.Why QD and QW structures are so critical for y Q Q

electrical excitation?For successful realization of electrical excitation two conditions should be satisfied: (i) effective and sustainableconditions should be satisfied: (i) effective and sustainable excitation of the crystal host by electrical current, and (ii) effective energy transfer from the host to the mid-IR lasing TM impurity.The phenomena of quantum confinement of the atomic impurity in quantum well and quantum dot active layers results in much more efficient transfer of energy from the h t t th l li d i it d t l i f

44

host to the localized impurity due to a large increase of exciton oscillator strength bound to the impurity center.

Future electrically pumped Cr and Fe doped Quantum Dot and Quantum well broadly tunable mid-IR lasersy

Molecular beam epitaxy

p‐ZnxMg1‐xSySe1‐y

Au electrode

p‐ZnS1‐xSex

2‐5 µm

1‐2 µm Guiding

en yen yn+‐ZnSe

n‐ZnxMg1‐xSySe1‐y

n‐ZnS1‐xSex

2‐5 µm Cladding

Cr:ZnCdSe

2 µm 3 µmwavelengthIn

tesi

ty2 µm 3 µmwavelength

Inte

sity

2-3 mm

P - Contact

p - Clad Layer

Nanocomposite

n‐GaAs substrate

In electrode

µ µgµ µg

~100 μm

Nanocomposite Active Region

n - Clad Layer

n+ - Substrate

N- Contact

GaAsn-ZnS

Chromium doped

p-ZnSe

Scheme of the Mid‐IR laser based on nanocomposite QW/QD C Z S d i l

SSDLTR’08, Mid‐Infrared Lasers

45

Scheme of the Mid‐IR laser based on QW Cr:ZnSe heterostructure.

GaAs Substrate ZnSe

m doped ZnCdSe QW

Cr:ZnSe ‐ conductive polymer structure prepared by layer by layer methodJ. of Luminescence 125, 184‐195 (2007)

Lasing of Cr2+:ZnSe via Ionization Transitions

ZnSeEac J. of Luminescence 125, 184‐195 (2007)

mV15

2025

0 2 4

Pump Pulse

Lasing μs

Build up timeLasing

from

ZnSeCB

Cr2+/Cr+

hνos5E

5T2

μs0 2 4 6 805

10 0 2 4Lasing from 532nm

g from 1560nm

μs532nm pumping

+

hνpump Cr2+*

5E

Cr2+*

μ0 6 8pumping pumpi

ng

un.

1

Lasing and Luminescence spectra under 532nm excitationVB

Ed

Time+ +

Cr2+:ZnSe1mmx4mm

95% R Flat Output Coupler

ensi

ty, a

b.u

2025

1

b.un

. Lasing from Luminesc

10cm Au Mirror

Lasi

ng In

te

101520

tens

ity, a

b 532nm pumping

ence from 532nm pumping

532nm, 5nsec pulse

10Hz rep rate

46PumpEnergy,mJ

5 10 1505

wavelength,nm1800 2000 2200 2400 2600 2800 30000I

n p p g

Mid-IR Electroluminescence of n-Cr:ZnSe (ASSP’06 WB21)Absorption Spectra Al:Cr:ZnSe I-V Curves for Cr-Al:ZnSe Samples # 1 & 2

10 mid-IR optical signal

K (cm

- 4

6

8

rent

(mA

)

246810

Sample#2

Sample#10

~7.5KΩ

lts

mid IR optical signal

1)

0

2

Wavelength (nm)1200 1600 1800 2000

Cur

r

-10-8-6-4-20

~30KΩ

Vol

-2Electrical pulse

-4Wavelength (nm)

Voltage(V)-80 -60 -40 -20 0 20 40 60 80

-10

Time (µs)-200 0 200

Visible Luminescence ofVZ -Al complex

mid-IR Cr2+ electroluminescenceVZn Al complex

nsity

, a.u

.

ensi

ty, a

.u.

Inte

n

Inte

Cr2+ optical pumping

47Wavelength (nm)Wavelength (nm)400 600 800 1800 2200 2600

Fabrication of II-VI NCD doped with TM (Cr, Co and Fe) ions by laser ablation method

The nanocrystals were fabricated from TM (Cr, Co, Fe) thermo-diffusion doped ZnS and ZnSe bulk crystals

ions by laser ablation methodC. Kim, D. V. Martyshkin, V.V. Fedorov, I. S. Moskalev, S. B. Mirov, J. of Spectroscopy, 22(9), 32-37 (2007).

crystalsAt the first step of NCD preparation, bulk polycrystalline samples were ablated by Nd:YAG laser with (1064nm) pulse durationLaser

b

H20

Filter

Peristaltic pump

laser with (1064nm) pulse duration 30 ps, repetition rate 10 Hz, and pulse energy of 10 mJ.At the second step of preparation nanoparticles suspension was

beamZnS

Filter

Filter nanoparticles suspension was sonicated in order to break large aggregate. The radiation of the third harmonic (355nm) of the Nd:YAG laser with 30 ps, 10 Hz,

Out

p , ,and 15 mJ.Precipitated nanoparticles were extracted from aqueous solution, washed with distilled-deionizer Experimental setup of Ⅱ-Ⅵ semiconductor

Laser beam

ZnS ArIn

water and dried naturally under ambient condition

Experimental setup of Ⅱ Ⅵ semiconductorNanocrystalline dot (NCD) fabrication by laser ablationbulk TM:II-VI in liquid. 48

First mid-IR luminescence of TM doped II-VI NCD We have developed technique for preparation of nanoparticles based on II-VI materials doped

FeCoCr

We have developed technique for preparation of nanoparticles based on II VI materials doped with TM ions with photoluminescence in mid-IR spectral region

FeCoCr

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0Wavelength, μm

RT luminescence spectra of a) Cr, b) Co and

C. Kim, D. V. Martyshkin, V.V. Fedorov, I. S. Moskalev, S. B. Mirov, J. of Spectroscopy, 22(9), 32-37 (2007).

c) Fe doped ZnSe NCs samples.

Lasing of 27 nm Cr2+:ZnS NCsLasing spectra and energy input-outputcharacteristics of 27 nm Cr2+:ZnS NCs. RTc a acte st cs o C S Csemission of the Cr2+:ZnS NCs under 1.56μm excitation with pump energy below (a)and at laser threshold (b), c) Spectrum ofthe RT lasing of the Cr2+:ZnS NCs, d)Output input dependence for RT gainOutput-input dependence for RT gain-switched Cr:ZnS NCs lasing. Thepumping beam size was 3 mmcorresponding to ~310 mJ/cm2 thresholdpump energy density.

27 nm250 nm

250 nm3 μm

nten

sity

27 nm Cr:ZnS NCs lasing

0 5 10 15 20 25 30 35

InLaser action was monitored by threshold behavior of intensity, emission spectra and shortening of emission lifetime

QELS’08 D. Martyshkin, et al., QFD2

0 5 10 15 20 25 30 35Energy (mJ)

Potential Applications1. The ability of the II-VI lasers to tune in and out of the strong absorption band of liquid

water will definitely make use for surgical applications: welding applications (power i t i 200 W hi h i l d il bl ) i l l l li tirequirement is ~ 200 mW, which is already available), or surgical scalpels applications

(~10 W, which is already available).

2. The ability of the II-VI lasers to tune in resonance with absorption of numerous organic molecules over 2-5 μm and in tandem with OPO over 2-15 μm spectral range make them

i i fpromising for:

Species-specific gas monitoring in production facilitiesSensing of pollution and chemical warfare agents; Monitoring of hazardous waste and munitions disposal Tracking of naturally occurring gas emitters - methane seeps and volcanoes Stand-off assessment of explosion hazards such as fuel leaks Oil prospectingMeasurements of medically important molecular compounds in the exhaled breath of patients, or other medical applications such as non-invasive optical blood glucose monitoring around 2.3 um pp p g gthrough the human skin.

3. The ability of the II-VI lasers to operate over windows of atmospheric transparency makes these lasers suitable for

Infrared countermeasures eyesafe seekers for smart munitions and cruise missiles; oratmospheric free space communications.

4. The combination of a high values of saturation cross-section (10-18 cm2), small saturation energy with good opto-mechanical (damage threshold - 2J/cm2) and physical characteristics of ZnSe and ZnS hosts make Cr and Fe2+ ZnSe/S cr stals an idealcharacteristics of ZnSe and ZnS hosts make Cr and Fe2+:ZnSe/S crystals an ideal materials for passive Q-switching of mid-infrared laser cavities.

ConclusionsRecent progress in transition metal doped II‐VI semiconductor materials(mainly Cr2+:ZnSe and ZnS) make them the laser sources of choice whenone needs a compact system with continuous tunability over 2‐3.1 μm,output powers up to 6W, and high (up to 70%) conversion efficiency.

The unique combination of technological (low cost ceramic material) andThe unique combination of technological (low‐cost ceramic material) andspectroscopic characteristics (ultra‐broadband gain bandwidth, high στproduct and high absorption coefficients) make these materials idealcandidates for “non‐traditional” regimes of operation such as microchip(output power up to 3W) and multi line lasing (lasing with any pre(output power up to 3W) and multi‐line lasing – (lasing with any pre‐assigned spectral composition‐dozens of lines).

Emerging Fe2+:chalcogenide lasers have potential to operate at roomtemperature over the spectral range extended to 3.7‐6.5 μm.p p g μ

Cr and Fe doped II‐VI lasers combine the versatility of the ion‐doped solid‐state lasers with the engineering capabilities of semiconductor lasers, paving the route to the future electrically pumped ultrabroad‐band solid‐t t l Thi k h th i iti l t t d hi i thi lstate lasers. This work shows the initial steps towards achieving this goal by studying Cr2+ ion excitation into the upper laser state 5E via photo‐ionization transitions as well as via direct electrical excitation. First mid‐IR luminescense of Cr, Co, and Fe doped quantum dots was demonstrated at RT 2 5 t l ll fi t l i f C d d Z S

52

RT over 2‐5 μm spectral range as well as first lasing of Cr doped ZnS quantum dots.

Future PlansOptimization of Cr/Fe:ZnSe laser ceramic. Cr:ZnSe/S Power scaling to 0.1-1 kW power levels 20 x 5 x 1-mm edge-pumped slab, with uniform heating, could dissipate as much as 1.6 kW of heat before fracturing. If we assume a pump laser at 1600 nm and a

Opt. Express 14, 11694-11701 (2006) J. of Spec. Top. in QE., 13(3), 810-822, 2007.IEEE J. of QE 42 (9), 907-917 (2006).J. of Luminescence 125J. of Spectroscopy, 22(9), g p p

Cr:ZnSe laser operating at 2400 nm, then 1/3 of the pump power is dissipated as heat, so the slab could be pumped with nearly 5 kW of pump before fracture.High output energy (tens of mJ tens of ns) gain

p py, ( ),184-195 (2007)

CO2 absorption14K

Fe:CdMnTeHigh output energy (tens of mJ, tens of ns) gain switched (room temperature Cr:ZnSe/S 2-3μm and Fe:ZnSe (3.8-5.2 μm) lasers.High output energy (hundreds of mJ, hundreds

Inte

nsity

, a.u

Pump Second Order14K

of μs) pulsed room temperature Cr:ZnSe/S (2-3μm) and Fe:ZnSe (3.8-5.2 μm) lasers.Er/Tm fiber pumped CW TE cooled Cr/Co/Fe ZnSe 3 8 5 2 m lasers FeC oC r

wavelength, nm

3500 4000 4500 5000 5500 6000 6500 7000

RT

Cr/Co/Fe:ZnSe 3.8-5.2 μm lasers.Multiline spatially dispersive Cr/Fe:ZnSe lasers.Search for new Fe:II-VI laser media promising for 3-7 μm gain switched lasing at RT

FeC oC rTM:ZnSe QD

for 3-7 μm gain switched lasing at RTElectrically pumped QD/QW 2-3μm Cr:ZnSe/S lasers.

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0W avelength, μm